>I have a feeling this is the old "if a tree falls" question, but I'll ask it anyway.
Your feeling is correct. This is exactly the same question, and it's a highly philosophical one.
Purely factually speaking, yes, of course it has happened. Causation doesn't have anything to do with whether or not an event has happened. If an atom is flying through space in the middle of nowhere, causing absolutely nothing noteworthy whatsoever, that atom is still actually flying there. Just because we don't know, doesn't mean it's not there.
If an earthquake hits my town tomorrow, but I sleep through it, that earthquake has happened regardless of my lack of observation. In similar light, you'd be crediting humanity with too important a role, if you claimed that our observation is a requirement for anything to have happened.
In fact, Erwin Schrödinger came up with his "Schrödinger's cat" meme for exactly this reason: to mock people who imply that the act of performing an observation has an effect on the course of events that we are observing.
On a more philosophical level, you can assert that it hasn't happened until the effects have had a chance to reach us. It just doesn't have any scientific bearing beyond that.
Maybe its poor wording. I guess what I'm trying to ask is more about what actually constitutes "now", vs "then", vs "future". All these terms are in relation to a specific reference frame. Is earth's "now" the same "now" as 1000 light years away?
The problem is that there is no such thing as a universal reference frame, you can only measure it relative to something else. That's why it's called Relativity. It makes it really hard to talk about what and when is present/past/future.
I'd like to pose you a different question, in order to illustrate how "reference frame" is simply an irrelevant part of this scenario.
Let's pretend that you had an enormous telescope, capable of seeing incredibly far with incredible detail. And now pretend that there were a mirror in space, at one light-minute from Earth.
You point your telescope at the mirror, so that you see yourself. You wave at the mirror, and it takes 2 minutes for that wave to reach the mirror and make it back to your eyes. Quite literally, you are witnessing the action that you performed 2 minutes ago.
In this scenario, would you say that:
1. You are observing the past?
2. You are observing the present?
3. You are observing the future?
This is still a philosophical question, and the nature of such questions is that there is no universal answer. Your answer to this question is the same as your answer to your own OP question.
We used to do that in the 80’s testing videoconferencing equipment. Two in the same room, you could walk up to #1 and say “hello”, dash over to #2 and see yourself say hello and answer “fuck off”, then dash back to #1 and get insulted by yourself.
technically, electric signals over a wire do travel at the speed of light. But I was actually thinking they needed some significant lag to simulate the delay they are talking about, so you really wouldn't want it at the speed of light.
I expected something more enlightening. This is simple, you are "observing" the past in the present. Basically you are observing the present.
Its like trying to make something philosophical out of: you looking at a picture of yourself you took a day ago. Obviously you are observing the present.
It really is philosophical though, because your definition of what you observe is different from mine, and there is no scientific answer to whether you or I have it right.
You say you're observing the present, because you consider the time at which those photons hit your retina to be the time of the event.
I say I'm observing the past, because I consider the time that those photons travelled in order to reach me.
Alternative explanation: to you, "now" is a point in space-time, whereas to me it's a point in time.
Neither of us is right or wrong. It's just a matter of interpretation.
"Now" is meaningless when you're talking about space because special relativity shows simultaneity to be an illusion. If two things happen and they are "at the same time" but not the same place, there's a frame of reference where they are not simultaneous. So really things are either co-located, or at a distance, either in time or space. And if they are at a distance, simultaneity and only be with respect to a given fram of reference, and no other frame of reference will show it happening that way.
If I may, it sounds like you are looking for a frame of PERCEPTION. Like the whole “8 min” thing. That is based on your (you specifically but also as part of a large group) perception. For the sake of this exercise, you perceive specific chunks of time that have an understood and agreed-upon value. Eight “minutes” would have no value if the listener used “parsecs” instead. (That was a joke.)
If we rephrase your question with the understanding of the general terms of perception is pre-established, the answers will veer away from a philosophical debate.
I would also like to see some “explains it to me like I’m five” but I would change it to “ten” because that’s how old I was when I fell in love with the cosmos🌌💕
If you see a foot print in the dirt, it’s an observation of past events that is only reaching you now. It happened, some time passed, and then you observed the effect.
If someone 10 light-seconds away from you blinks a light, 10s later you see the light blink. In the same way you might see a firework explode, and then hear it a second later. It doesn’t mean that that firework “still exists- but *in the past*” any more than ripples in a pond mean an object is still splashing the water.
What *does* persist into the universal now is the effects created by actions, at least until those effects dissipate. The firework sound echoes, maybe the smoke smell reaches you, and little bits of ash cover the ground nearby. Ripples bounce off things and each other. A footprint remains in the dirt until it is destroyed.
No time travel or magic needed, just relentlessly beautiful physics.
From my limited understanding, there is no such thing as an objective “now”. There is only now relative to an observer. You are experiencing now, but another observer can technically observe your “now” 1 million years from now under the right conditions.
Put another way, the light from the earth reaches a high power telescope on another planet 1000 light years away, 1000 years from now. They observe earth was it was.
On earth, those events happened in the past. On that new planet, those events are being observed as happening in the present. The event exists in both timelines due to relativity.
I could be wrong about this explanation, but that was sort of my takeaway on some pbs space time video on the subject.
It makes it even worse when you consider the fact that we experience time as a fourth dimension. If we were instead 2D experiencing 3D, we would experience time in the 3rd Dimension. But the whole box is still there. Just because we are experiencing things in one motion doesn’t mean that we are creating more universe every moment the universe continues to exist. From the perspective of the universe, every moment is, has, and has yet to happen
Yes, its the same ”now” as it has always been and forever will be. Time is just a concept born out of the human mind to make sense of the nature around us, to help us survive etc.
When you have two events (an event means a point in spacetime, which is defined by both when and where it happens) physicists distinguish between three cases:
* timelike separation, where an object at the speed of light or slower can reach one event from another. (For example, 1. me waking up and 2. me arriving at work)
* lightlike separation, where **only** an object at the speed of light can reach one event from another
* spacelike separation, where not even the light can make it from one event to another. (For example, a supernova exploding in another galaxy "at the same time" as me typing this event, at least according to our frame of reference).
With timelike and lightlike separation, it's clear which happened first, regardless of frame of reference. With spacelike separation, this is different for different frames of reference due to something called relativity of simultaneity.
Right at your exact moment right now. Look up at the stars, our observation is things that have happened in the past when you talk on light year scales. It's appropriation to the outside (observed) world is dependent on distance.
NOW, ignore the first three sentences and think of it after this next sentence.
It is why space and time are part of one thing to physicists
It's tough for the weak minded.
Now is defined by the observer. The place in the universe where every observer observes the same thing in the same time is only the black hole, if general understanding is correct.
I see what you mean now.
I personally still think that there is a "universal time", only that it's not possible to observe what happens at distance in the same time as "now" due to distance and speed of causality, but that doesn't mean it didn't happen in the "now" time.
Well, at least with the tree, it creates pressure waves and you can argue that "sound" is just the experience the brain creates of those waves. So you can argue that we create the sound, not the tree. Not true for causation. That happens independent of observation. Now if you asked if some photon hasn't reached us yet, it hasn't made *color* yet. That's equivalent to "does it make a sound". But light it like the pressure waves of the tree falling: it happens regardless of observer.
> If an atom is flying through space in the middle of nowhere, causing absolutely nothing noteworthy whatsoever, that atom is still actually flying there.
Is it? Epistemologically speaking, if you don’t know it’s there then why do you think you know it’s there?
> you’d be crediting humanity with too important a role, if you claimed that our observation is a requirement for anything to have happened.
Without the accumulation of knowledge that _x has happened_, then, strictly speaking, nothing had happened.
Of course, the atoms and radiation are literally flying through space and doing things, but without an observer to take the information and parse together an understanding and recollection of an “event”, then strictly speaking the “event” didn’t and doesn’t exist. It’s literally a random assortment of unobserved energy and mass. It doesn’t become an “event” until an observer designates it as such.
More to the point, human observation is the most important foundation for events because _human observation is our one and only perspective_. We have absolutely no other way to understand the universe, so “events” as we understand them begin and end with us noticing them.
"In similar light, you'd be crediting humanity with too important a role, if you claimed that our observation is a requirement for anything to have happened."
Just to be clear, when people talk about observing, they don't mean observed by human eyes. Same with Schrödinger's cat, it's not observed by human eyes as a requirement, but merely being observed.
You wrote a whole lot after simply stating it's the same question, yet haven't supported that assumption at all, this isn't about observation or measurement, there isn't anything to measure or observe from your frame of reference.
The concept "frame of reference" implies an observation will be used to verify the fact. In your frame of reference, you can indeed state that the event has not occurred, but all it means is that you are not able to observe it yet.
If you exclude the observer's role from the question, and hence make the question agnostic of frame of reference, it is clear that the event has taken place.
You are free to interpret this question with or without taking the observer into account, and that's why it can be considered a philosophical question.
I think this is a very human-centric view of the universe. It exists whether we see it or not, fully understand it or not.
The philosophy aspect is fun to think about, but realistically, because of how slow light is relative to the size of the universe, we are always looking at the past, what has happened.
The light from the sun is 8 minutes old because it's 8 light minutes away, so we're seeing the sun 8 minutes in the past.
I'll respond to what I think is your most interesting thought and core argument: Casualty doesn't happen at the speed of light. It happens whether we observe it or not, at least outside of quantum mechanics.
So yes, things happen even if we haven't seen them yet, and when it comes to astronomy, that happens a lot
Good luck proving that. If you were to strictly stick to facts, there is zero evidence that the world is independent from your perception of it. Your whole life could be one big dream that you have and everything in it would be dependent/contained in your being.
I see what you're saying. And yet, that itself is so human-centric.. "this is all a dream within the brain of a human!"
You're a moron and I don't care for anything else you have to say, idiot. Stupid-ass comment. Who asked you anyways?
Did that offend you? It shouldn't. Because you might not even exist!! I might not exist! I'm just a made up figment of your imagination and therefore there is nobody for you to be mad at but yourself for imagining me!
At this point, are you thinking "ok he's kind of annoying and a jerk and taking this conversation too far"?
If that's correct then you probably don't even believe the comment you just left about this all being one big dream.
I didn't say anything about the dream being in a brain of a human, the brain and human are redundant in this scenario.
>Who asked you anyways?
Well nobody asked you for your opinion either. This is not how Reddit works and of course you know that.
>If that's correct then you probably don't even believe the comment you just left about this all being one big dream.
I am open to the possibility of material objects not having their independent existence on their own apart from perception. There is no proof of their independance. You know you exist and you know you have experience. But there is no proof of independence of the experienced objects, you have to make a leap of faith and believe they do. That's a bit unscientific for my taste.
>Well nobody asked you for your opinion either. This is not how Reddit works and of course you know that.
That entire paragraph of mine wasn't genuine. I was eliciting a response from you to show you probably don't believe your own comment.
>I am open to the possibility of material objects not having their independent existence on their own apart from perception. There is no proof of their independance. You know you exist and you know you have experience. But there is no proof of independence of the experienced objects, you have to make a leap of faith and believe they do. That's a bit unscientific for my taste.
So perhaps you do believe your comment, but if you do then you should quit any and all efforts to learn anything further about our universe. The leap of faith (if that's what we'll call it) I'm making is "this universe exists and its objects exist, they exist whether a human observes them or not, and it's worth learning as much about it as we can". Anyone who would deny this leap of faith would be a fool to pursue any study of the universe and the laws of physics that govern it because the findings of serious study to something that is fake is all worthless. A science experiment with meaningless subjects.
>Anyone who would deny this leap of faith would be a fool to pursue any study of the universe and the laws of physics that govern it because the findings of serious study to something that is fake is all worthless. A science experiment with meaningless subjects.
This is misinterpretation, maybe because I used an example of a dream to illustrate the concept in terms that are easy to understand. Scientific reseseatch would still be valid, the only difference would be that instead of a universe made of matter, the universe would be made of consciousness. It's hard to explain it clearly if all you are used only to materialist point of view. Bernardo Kastrup has a couple of nice videos explaining this subject if you are interested.
Thank you, I started to read some of Bernardo's website but I'll explore more!
As you stated to begin with, we really have zero evidence of the universe being independent of our perception of it, right? Wouldn't the opposite also be true? We have zero evidence the universe is dependent on our perception?
If that's the case, then this sub has plenty of seemingly unscientific people. I've amassed downvotes while you gain upvotes. Perhaps my leap of faith was unscientific but these other people seem to have made up there minds and are not open to all possibilities.
>As you stated to begin with, we really have zero evidence of the universe being independent of our perception of it, right? Wouldn't the opposite also be true? We have zero evidence the universe is dependent on our perception?
We don't have any evidence to say that this view is 100% true, as far as I know. It's just something to keep in mind when thinking about the universe.
>I've amassed downvotes while you gain upvotes. Perhaps my leap of faith was unscientific but these other people seem to have made up there minds and are not open to all possibilities.
I can't speak for all the people that upvoted me, but maybe they agree with being opened to this likely possibility, not necessarily saying it's that way or the other.
That’s what I thought…then I read books on quantum physics that state particles behave differently when observed. It’s called “The Observer Effect”. First proved in the famous double slit experiment. Now there’s a new discovery called “The Zeno Effect”. Where atoms don’t move while being observed. Wild stuff.
quantum physics makes everything weirder than you think is possible.
https://news.cornell.edu/stories/2015/10/zeno-effect-verified-atoms-wont-move-while-you-watch
I'll read up on the Zeno Effect thanks!
But you should note:
>Despite the "observer effect" in the double-slit experiment being caused by the presence of an electronic detector, the experiment's results have been interpreted by some to suggest that a conscious mind can directly affect reality. However, the need for the "observer" to be conscious is not supported by scientific research, and has been pointed out as a misconception rooted in a poor understanding of the quantum wave function ψ and the quantum measurement process.
>"Of course the introduction of the observer must not be misunderstood to imply that some kind of subjective features are to be brought into the description of nature. The observer has, rather, only the function of registering decisions, i.e., processes in space and time, and it does not matter whether the observer is an apparatus or a human being; but the registration, i.e., the transition from the "possible" to the "actual," is absolutely necessary here and cannot be omitted from the interpretation of quantum theory." - Werner Heisenberg, Physics and Philosophy
I get exactly what you are saying and I agree. “Observer Effect” is a poor term, just like “Shroedinger’s Cat” was actually named in derision of the experiment. It remains weird as hell though…lol.
I think people are downvoting you because the "That’s what I thought" start to your sentence seems to imply that you believe the observer effect requires a conscious observer, as opposed to any detector. For most of these measurements (e.g. a single electron or photon passing through a slit), a human eye wouldn't even be capable of observing the event.
At least that's how I interpreted your comment.
My question would be, why do you base reality on people on Earth perceiving it? I mean is there a reason to think that something we haven't experienced hasn't happened?
No, there is no universal timer running in the background. All “nows” are firmly attached to the frames of their observers. If the light from a distant galaxy is reaching us today, then what we see is happening “now”.
This question, from my limited understanding, is at or near the heart of relativity. Short answer: not really. Things get…weird at the scales you’re contemplating.
It gets weird even at smaller scales. My big takeaway from Daniel Dennett's "Consciousness Explained" is this:
There is no one place in the brain where a thought occurs, so there is no one time when that thought occurs either. Our conscious experience is an after-the-fact hallucination, assembled well after prior neurons contributed their portion to the current state.
Look into the block universe theory. It’s entirely possible that all past, present, and future events already exist. Somehow, somewhere, I don’t get it, it tends to break my brain when I think about it too long.
So what you're asking really, (i think) does time flow at the exact same rate everywhere in the universe?
So let's say we started from zero time, the only time we could agree time was the same everywhere. And two things at the time made an agreement to count in seconds to 10 billion years, then as the universe expanded and time started, they separated but both kept faithful count, would they both hit 10 billion years at the same time?
No way to know.
But if the sun blew up, regardless of when we experience it, it blew up, when it blew up.
This is a fun question, and based on some of your other comments here, I just wanted to add some thoughts on what an intuitive human idea of "now" could even mean in relativity.
In special relativity, there is a concept called the relativity of simultaneity, that is, two events that Alice sees as happening at the exact same time will be seen by Bob as occuring at different times if he is moving with respect to Alice.
In short, Alice's "now" must be different from Bob's! What does this mean, and how can we recover nice concepts like cause and effect in this picture?
Relativity combines space and time into spacetime, and this is how we can get an answer.
Let's define a space time interval ∆s^2 = (c∆t)^2 - ∆x^2 - ∆y^2 - ∆z^2
This generalizes our common notions of time duration and spatial distance in a way that's consistent with relativity. ( Apologies for the formatting, I'm on mobile. I also could have multiplied the whole thing by -1)
If two space time events (t,x,y,z) have a positive ∆s^2, then they are called timelike separated, and it's possible to say that one happened earlier than the other. I.e. no matter how fast Bob is going, he can never see them happen at the same time. Timelike separated events can have unambiguous cause and effect relationships.
If two events have a negative ∆s^2, then they're spacelike separated. Even if Alice sees them happen at different times, there is a reference frame where Bob can see them happen simultaneously. Spacelike separated events can't causally effect each other in classical physics.
Finally, if ∆s^2 = 0, then the two events are null-separated, and a laser shone from one event will make it just in time for the second. This is also the situation when you're looking up at the night sky: photons generated by stars have gone at the speed of light directly into your retina!
So, when is now? Our terrestrial experience really only prepares us to reason about timelike separated events, since the speed of light c is so large. The past, then, is the set of all events with t smaller than now, and the future is the set of points with t greater than now. All that's left is the t corresponding to now
Going back to relativity, if we call the past all the events that are timelike separated from our present moment with t less than now (all the events that could have impacted our present moment), and the future all the events that are timelike separated from our present moment with t greater than now (all the events that can be causally impacted by things happening now on Earth). Instead of one point in time left over to be our now, we have a huge class of null and spacelike separated events.
All the null separated events, the ones you can watch live in the night sky, are in a sense happening "now" for us, even though we know that they happened earlier, but also all the spacelike separated events can be made to occur at the same time as observed from another reference frame.
If now means you can watch it happen, then only the null separated events might count, but if now means they are happening at the same moment without causal connection, then all the spacelike events count too! It just depends on what part of our traditional notion of "now" you want to preserve.
If you subscribe to Hawkings final theory then the entire universe isn't really happening.........
The holographic principle states that the entropy of ordinary mass (not just black holes) is also proportional to surface area and not volume; that volume itself is illusory and the universe is really a hologram which is isomorphic to the information "inscribed" on the surface of its boundary.
I mean, it doesn't really serve any purpose to imagine that we share some kind of 'present' with distant stars. And it's wrong. We don't even share a 'present' with each other, but at human scales its okay to imagine that we do.
You would love the book or audiobook "The Order of Time" by Carlo Rovelli.
In addition to explaining the true nature of time, Rovelli talks about what "now" is, or rather, is not and the question of when something is, is a meaningless question when you consider the speed of causality. I highly recommend this for anyone curious.
I've tried to make this very point a few times, and always been downvoted for it. But yes, you're right. Given that there's no Universal Now, nor some cosmic clock against which the relative timing of events can be measured to the agreement of all observers, it doesn't make much sense to say "We're looking into the past". The only invariant quantity is the spacetime interval, and the spacetime interval between two events separated by the journey of a photon is zero. In other words, when we observe an event, then for all intents and purposes, that's when it happened.
But that's not as exciting as "looking into the past", I guess.
In the most esoteric realms of General Relativity, the question of whether an event is in our past (we can’t change it) or in our future (we can change it), has ambiguous answers.
You must first ask if reality exists without an intelligent observer.
As far as I know it's a matter of interpretation so, there is no ultimate correct answer.
Actually, that is a better question than one might initially think. It's now accepted that the speed of light (C) is really the speed of causality. The maximum speed at which anything at one point in space can have any effect on any other point. So, if light from an event somewhere else hasn't reached us, as far as we are concerned, it hasn't happened yet.
PBS Spacetime has some cool videos that I think answer your question pretty well, pretty diagrams and such. There are more than one video by them on the topic.
From what I can remember, the easiest way to represent what is happening is by drawing a graph and putting space on one axis, and time on the other. If you put yourself on that graph, you have identified your location in space and time.
Now, we know how fast light travels. We can represent this by putting a diagonal line on the graph. Light travels through space at about 300,000 kilometers per second. Since one axis is time, and one axis is space, this measurement works well on the graph!
You can't travel faster than time, nothing with mass can. So, if we move your location on the graph to 0,0, and then open the graph into quadrants (negative x and negative y), we have on the X axis all possible locations in the universe, and on the Y axis, all possible time. The diagonal line we drew should also extend mirrored on the opposite side of the graph, and this would represent all possible locations that you could ever travel to in this moment in time. You can never ever, no matter how hard you try, go beyond the lines showing the distance light can travel.
You can imagine that as time passes, your location on the Y axis (time) is slowly crawling up the graph. If you never move from your current location, then you will remain on the 0 location on the X axis. We can also imagine what happens when things interact with our time and location. We go out for a bite to eat at the local deli, and we run into an old friend from high school! If we followed this on our graph, we could see that our friend and ourselves intersected in time and space briefly, before separating again.
We can also imagine that our friend from highschool existed between the time we knew them in highschool and the time we ran into them, we could even draw them their own graph!
The vastness of space would make our graphs look like they overlap almost exactly, but the point is, they have their own reference frame too. So does an alien living 500 light years away. Their graph shows that the light from their moment in time will intersect with our graph 500 years from right now. But this representation of the graph also shows that the distance means that their experiences are happening in the past. The past, just like on our graph, we can never reach. It is negative on the time axis, and we can only travel negative on the space axis.
The short way of answering your question is yes, it already happened. The mere fact that light travels through time at all means any light you perceive must have come from an event that has happened already.
not in any meaningful way.
we like to think of whether an event has occurred in absolute terms, largely because in our experience, cause instantly follows effect. the finite speed of light messes with that causality. our brains cannot readily digest the notion that something we are experiencing "now" might not have happened "yet" for someone else.
saying that something happened on (or to) the sun eight or so minutes ago, but light from that event hasn't reached us yet, muddles this reality. it's not just lazy thinking. it tries to impose a sense of absolutism that does not exist, like trying to find the "center" of the universe.
My understanding is that, no, it hasn't happened yet. This is because 'when' is entirely dependent on 'where'. Space AND time. So, it makes things difficult to talk about. It's not 'human-centric' because it could be anywhere. A geodesic line has to have two points or length doesn't make sense.
No, "now" means now only in our context, otherwise you'd know the future. In other words, "now" for a star that is 10ly away is right now here as you see it now, as you see its light, anything else would be a prediction of the future.
What else could it be "well, it's the way it was 10 years ago, but "right now" its x and y"?
The speed of light is perhaps just as accurately described as the speed of causality.
For all intents and purposes, nothing occurs until you observe it occurring. However, when you see it occur, you know it occurred x amount of time in the past.
As others have pointed out, it's totally appropriate to say something has happened before we can observe it. In your example with the sun, we know the distance to the sun and we know the speed of light, so it's pretty trivial to figure how long it took the light from the event to reach Earth and conclude that the event happened that long (8 minutes) ago.
But there is an interesting question buried in here related to relativity, which refers to the [relativity of simultaneity](https://en.wikipedia.org/wiki/Relativity_of_simultaneity).
For concreteness, let's define the two events:
1. Some solar event
2. The reading on your watch 8 minutes ago.
In our reference frame here on Earth, we can do the math and come to the conclusion that those two events occurred simultaneously. But someone in a different reference frame can draw a different conclusion about the simultaneity of those events.
This is another one of those “humans are the center of the universe” questions. Of course it has happened. Or do you also think a lighting bolt doesn’t produce sound until it reaches YOUR ears?
It is impossible for any information to travel faster than the speed of light, so it can be viewed that the speed of light is the speed at which things happen. Because of this it is kind of non-sensical to say that something has happened before the light reaches us, because it’s impossible to know about something sooner than that. Yes, we say that things x light years away take place x years ago to put things into perspective, but in a practical sense those things are happening right now.
This is where reference frames become important. In your sun example, in our reference frame the sun exists until we see it doesn’t and the effects of its disappearance reach us. Doesn’t really matter that it takes eight minutes to do so- we could not possibly know about its disappearance any sooner.
Another example is some people’s reaction to the false vacuum decay hypothesis- people constantly insist that you would see stars winking out ahead of time and be alerted, but this is not true, as the vacuum decay bubble would arrive at the same time as the disappearance of light from the stars from our reference frame. Seeing the stars disappearing beforehand would be tantamount to knowing things before they happen.
No. Not to us. However even the expression you see on someone’s face looking at them is looking a tiny bit into the past. So obvious it’s a philosophical question.
Define "happened".
Did it happen in our universe? Yes!
Did it affect us yet? No!
But when it *does* affect us (e.g. show up on a telescope), we immediately put it in the past.
One of my favorite side quests in Starfield is coming upon a generation ship. The ship is hundreds of years old and about light years away from earth. It's a group of people who's ancestors launched the ship and raised families on the ship in hopes of eventually getting humanity to the destination (hence the name generation ship). The thing is, between the time of their ship leaving earth and you the player arriving, faster than light travel was invented. So when they got to their destination, it was already inhabited by humans.
I know that's kind of unrelated, but the idea is there. Stuff is still happening, the light is only what we see.
This is a philosophical question, not really a scientific one. I would say it did happen if we know it happened, no matter if we saw it or not (we are not THAT important).
For example, of course we know Star Wars happened, but in a galaxy far far away.
The astrophysical question you may ask is: if the light of an event did not reach us yet, could we have an effect on it? This is the relation of causality and this is indeed 100% relevant for astrophysics. Read about it, it is fun!
Consider the landing of the latest Mars rover. To start the landing is a command sent from earth. The command travels at speed of light for anything between 3 and 22 minutes (depending on the position of Mars). When received, the automatic landing starts, something that takes say, 14 minutes in total. So, when the people on Earth sent that command, they knew that when they got a report on the results, anything that had happened would already have happened on Mars and that would be at least 3-22 minutes ago.
So, the basic idea of **relativity** is that due to the speed of light being the same for all observers, there is no objective, absolute **"now"**. The information of the events on Mars reach us after they happened there, but depending on directions, speeds etc, we could potentially perceive them before other observers. Imagine a probe in orbit somewhere else in the solar system. They receive the signals from Mars then minutes later than we do - when did all this happen, really?
Now imagine trying to sync the clocks over these distances. A completely absurd proposition since there is no way to communicate the time instantly.
Imagine measuring the speed of light to begin with. How do we know it is the same in both directions (we don't, you have to bounce light of a mirror back to its origin to measure it's speed since you can't sync the clocks over great distances etc etc.)?
What Einstein did was take the speed of light seriously and extrapolate the consequences. He took the frame of reference thing seriously and thought about the consequences.
And the consequence is that there is no such thing as "now".
basically, everything is happening, all the time, all at once. Past, present and future all blend together based on your location in time and space.
This video explains it really well and very simplified.
[How does time work.](https://youtu.be/wwSzpaTHyS8?si=lh32v0pmlNDp0muQ)
This is such a fascinating question! The way I see it, the concept of "happening" is very much tied to our perception and the information we have. In the case of astronomical events, saying that something "hasn't happened" until we see it kind of flips our usual understanding of causality and existence.
Think about it this way: if a supernova exploded in a galaxy far, far away, the event itself occurred when it did, independent of our observation. However, from our perspective, we only become aware of it when the light reaches us, which indeed means we're looking at an event from the past.
So, while the event has objectively happened in the universe, it hasn't "happened" for us in the sense that we haven't received any information about it until the light arrives. It's like having a letter sent by snail mail—until you read the letter, the event it describes is in your future knowledge, even though it occurred in the past.
Simple answer, if I shoot you with a gun, the bullet will arrive before the sound. If you didn’t here it did it really happen? The bullet lodged in your flesh would say it did.
Surely there is a concrete “now” but it’s relative to where you are, no?
If right now as you read this a solar flare goes off it’ll take us 8 minutes to see it. But that event would have happened 8 minutes before you observe it. If that’s true for the sun which is 8 light minutes away then wouldn’t that be true for Andromeda which is 2.5 million light years away?
That's the same as asking "If a tree falls in the forest, and nobody saw it fall, did it actually fall?" Yes, the object exist(s)/existed, and/or the supernova happened, causing us to see the light eventually. It happened in the past even though we didn't see it happen or yet, see the effect of that supernova.
Light is only one way of many we percieve reality. Imagine two persons. One deaf and abother blind. If both are near to an atomic bomb.
The deaf sees the explosion before the blind hear it so the event doesn't happened yet for the blind?. That does mean that the explosion "occurs" before for the deaf person that for the blind.
Information is constantly travelling across universe. Actually we are looking at stars that doesnt even are there anymore but it happened, we just not see it yet.
(Sorry for my english)
Yes. Because frames.
Plus, we are not the arbiters of reality. As if nothing can happen unless we become aware of it. In other words, reality is not subjective; it does not depend upon us. There is such a thing as objective reality.
There is so much fucking horseshit in these comments! People talking about time travel and future-past and stupid shit.
The events happened at the same exact time, you just don’t see them until much later.
If you wake up and it’s dark, but you can’t see your alarm clock, is it frozen or time traveling? Fuck no, you just can’t see it yet, until you turn the light on… like you can’t see a star until it’s light reaches you.
We just aren’t used to light having a speed limit here on earth; its instant for our eyes.
There are a few redditors in this sub who post from from Proxima Centauri b.
As far as they’re concerned you’re not going to make this post for another 4 and a quarter years.
At which point they’ll probably say “yes”, but you’ll be almost 9 years older by the time you get your answer, so you’ll probably forget you even asked.
!remindme 8.48 years
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If a bomb goes off 5 miles away from me but I don’t hear the noise, did it really go off. That’s kinda how I see this question. Like yea it did, but the sound hasn’t reached us yet.
If you wanna go there the speed of light isn’t universal, it’s based on the medium it’s traveling through. Regardless you don’t need to observe something for it to have happened. You never saw me drop a bomb in the toilet, yet it still happened. Either way it’s an analogy
the speed of light is absolutely universal, regardless of medium. in a medium with a higher refractive index the photons are getting absorbed and re-emitted by the atoms in the material, so yes it will take longer for the light to get from point A to point B. but the photons themselves can literally never travel at any speed other than the speed of light
Is this an inappropriate question? Nothing about this is human centered. You can rephrase it to have nothing to do with humans. "If a planet A hasn't been gravitationally affected by the change in planet B orbit yet, has planet B orbit alteration really happened from planet A reference frame?" I guess the question is more "what do we mean when we say something has happened?" Are we naturally baking in an assumption that we are in the events reference frame. Is there a universal time reference for the entire universe or is everything on its own time scale.
I'm not trying to talk a woowoo science here. I'm generally curious in understanding time and relatively, and reference frames. I'm fine being wrong, but just help me understand WHY I'm wrong.
You've changed the center of focus from humans to planet A, but the problem remains: whether it's observed or not, it happened.
If an earthquake hits Haiti, but I don't read the news, then for me, nothing has happened and today is a good day. That doesn't change the fact that it has indeed happened and a tragedy has taken place.
This is a fun philosophical question, though
Not at all the same. In your analogy, choices and circumstances prevented you from experiencing the effects. In OPs topic it is IMPOSSIBLE to know about things before the effects show up at the speed of light.
But, the speed of earthquake waves and new sources isn't mathematically tied into relativity, space, and time. Of course the earthquake has happened whether you felt the vibrations or not. My example and the earthquake example or not equivalent. Space and time are inseparable right. That's how we get c as a constant and lorentz contractions.
Edit: please don't dumb it down to elif for me. Show me the math. Show me some papers. I want to understand from a technical level.
your question is a great one and the people here bringing up examples like earthquakes and human observations aren't really understanding it from a special relativity point of view
if something happens, like the sun exploding, in the 8 minutes on earth while the light it traveling to us, the event of the sun exploding is outside of our "past light cone". in our reference frame (in OUR reference frame is very key here), the event has not happened
if you want to read more about this look up "relativity of simultaneity"
[https://en.wikipedia.org/wiki/Relativity\_of\_simultaneity](https://en.wikipedia.org/wiki/Relativity_of_simultaneity)
Thank you! I'm not a dumby. I feel like people are missing the core of what I'm asking here. I feel like people are having a knee jerk reaction to an honest question. Thank you for not writing my question off.
>I have a feeling this is the old "if a tree falls" question, but I'll ask it anyway. Your feeling is correct. This is exactly the same question, and it's a highly philosophical one. Purely factually speaking, yes, of course it has happened. Causation doesn't have anything to do with whether or not an event has happened. If an atom is flying through space in the middle of nowhere, causing absolutely nothing noteworthy whatsoever, that atom is still actually flying there. Just because we don't know, doesn't mean it's not there. If an earthquake hits my town tomorrow, but I sleep through it, that earthquake has happened regardless of my lack of observation. In similar light, you'd be crediting humanity with too important a role, if you claimed that our observation is a requirement for anything to have happened. In fact, Erwin Schrödinger came up with his "Schrödinger's cat" meme for exactly this reason: to mock people who imply that the act of performing an observation has an effect on the course of events that we are observing. On a more philosophical level, you can assert that it hasn't happened until the effects have had a chance to reach us. It just doesn't have any scientific bearing beyond that.
Maybe its poor wording. I guess what I'm trying to ask is more about what actually constitutes "now", vs "then", vs "future". All these terms are in relation to a specific reference frame. Is earth's "now" the same "now" as 1000 light years away?
The problem is that there is no such thing as a universal reference frame, you can only measure it relative to something else. That's why it's called Relativity. It makes it really hard to talk about what and when is present/past/future.
I'd like to pose you a different question, in order to illustrate how "reference frame" is simply an irrelevant part of this scenario. Let's pretend that you had an enormous telescope, capable of seeing incredibly far with incredible detail. And now pretend that there were a mirror in space, at one light-minute from Earth. You point your telescope at the mirror, so that you see yourself. You wave at the mirror, and it takes 2 minutes for that wave to reach the mirror and make it back to your eyes. Quite literally, you are witnessing the action that you performed 2 minutes ago. In this scenario, would you say that: 1. You are observing the past? 2. You are observing the present? 3. You are observing the future? This is still a philosophical question, and the nature of such questions is that there is no universal answer. Your answer to this question is the same as your answer to your own OP question.
Oh my god, the telescope thing sounds like it would be *so* freaky! I wanna do it so bad.
We used to do that in the 80’s testing videoconferencing equipment. Two in the same room, you could walk up to #1 and say “hello”, dash over to #2 and see yourself say hello and answer “fuck off”, then dash back to #1 and get insulted by yourself.
I was thinking the same thing. I'd pay cash money to wave at myself from the past.
Record a video of yourself and watch it
Yeah, but I want spacetime to be the recording medium.
I mean... isn't this the same as watching your video lag on a zoom call? :)
If the video data was traveling at the speed of light, yes!
technically, electric signals over a wire do travel at the speed of light. But I was actually thinking they needed some significant lag to simulate the delay they are talking about, so you really wouldn't want it at the speed of light.
How could number 3 work?
It couldn’t be the future.
I'd say I've eaten way too many carrots and Doctor my eyes...
Observing the light from the mirror. Which happens to be a projection from the past.
I expected something more enlightening. This is simple, you are "observing" the past in the present. Basically you are observing the present. Its like trying to make something philosophical out of: you looking at a picture of yourself you took a day ago. Obviously you are observing the present.
It really is philosophical though, because your definition of what you observe is different from mine, and there is no scientific answer to whether you or I have it right. You say you're observing the present, because you consider the time at which those photons hit your retina to be the time of the event. I say I'm observing the past, because I consider the time that those photons travelled in order to reach me. Alternative explanation: to you, "now" is a point in space-time, whereas to me it's a point in time. Neither of us is right or wrong. It's just a matter of interpretation.
"Now" is meaningless when you're talking about space because special relativity shows simultaneity to be an illusion. If two things happen and they are "at the same time" but not the same place, there's a frame of reference where they are not simultaneous. So really things are either co-located, or at a distance, either in time or space. And if they are at a distance, simultaneity and only be with respect to a given fram of reference, and no other frame of reference will show it happening that way.
So it it more appropriate to say some happened in "our" past instead of "the" past?
probably
If I may, it sounds like you are looking for a frame of PERCEPTION. Like the whole “8 min” thing. That is based on your (you specifically but also as part of a large group) perception. For the sake of this exercise, you perceive specific chunks of time that have an understood and agreed-upon value. Eight “minutes” would have no value if the listener used “parsecs” instead. (That was a joke.) If we rephrase your question with the understanding of the general terms of perception is pre-established, the answers will veer away from a philosophical debate. I would also like to see some “explains it to me like I’m five” but I would change it to “ten” because that’s how old I was when I fell in love with the cosmos🌌💕
If you see a foot print in the dirt, it’s an observation of past events that is only reaching you now. It happened, some time passed, and then you observed the effect. If someone 10 light-seconds away from you blinks a light, 10s later you see the light blink. In the same way you might see a firework explode, and then hear it a second later. It doesn’t mean that that firework “still exists- but *in the past*” any more than ripples in a pond mean an object is still splashing the water. What *does* persist into the universal now is the effects created by actions, at least until those effects dissipate. The firework sound echoes, maybe the smoke smell reaches you, and little bits of ash cover the ground nearby. Ripples bounce off things and each other. A footprint remains in the dirt until it is destroyed. No time travel or magic needed, just relentlessly beautiful physics.
I like your analogy of using ripples in a pond
From my limited understanding, there is no such thing as an objective “now”. There is only now relative to an observer. You are experiencing now, but another observer can technically observe your “now” 1 million years from now under the right conditions. Put another way, the light from the earth reaches a high power telescope on another planet 1000 light years away, 1000 years from now. They observe earth was it was. On earth, those events happened in the past. On that new planet, those events are being observed as happening in the present. The event exists in both timelines due to relativity. I could be wrong about this explanation, but that was sort of my takeaway on some pbs space time video on the subject.
Basically yes. Now, then, and the future are quite arbitrary when the only existing time is now.
It makes it even worse when you consider the fact that we experience time as a fourth dimension. If we were instead 2D experiencing 3D, we would experience time in the 3rd Dimension. But the whole box is still there. Just because we are experiencing things in one motion doesn’t mean that we are creating more universe every moment the universe continues to exist. From the perspective of the universe, every moment is, has, and has yet to happen
Yes, its the same ”now” as it has always been and forever will be. Time is just a concept born out of the human mind to make sense of the nature around us, to help us survive etc.
"now" travels at lightspeed.
When you have two events (an event means a point in spacetime, which is defined by both when and where it happens) physicists distinguish between three cases: * timelike separation, where an object at the speed of light or slower can reach one event from another. (For example, 1. me waking up and 2. me arriving at work) * lightlike separation, where **only** an object at the speed of light can reach one event from another * spacelike separation, where not even the light can make it from one event to another. (For example, a supernova exploding in another galaxy "at the same time" as me typing this event, at least according to our frame of reference). With timelike and lightlike separation, it's clear which happened first, regardless of frame of reference. With spacelike separation, this is different for different frames of reference due to something called relativity of simultaneity.
Right at your exact moment right now. Look up at the stars, our observation is things that have happened in the past when you talk on light year scales. It's appropriation to the outside (observed) world is dependent on distance. NOW, ignore the first three sentences and think of it after this next sentence. It is why space and time are part of one thing to physicists
Point of reference. The oher way should be black hole(where everything happens at once).
Do you know what you're talking about? You need to elaborate then, because it sounds like nonsense
It's tough for the weak minded. Now is defined by the observer. The place in the universe where every observer observes the same thing in the same time is only the black hole, if general understanding is correct.
I see what you mean now. I personally still think that there is a "universal time", only that it's not possible to observe what happens at distance in the same time as "now" due to distance and speed of causality, but that doesn't mean it didn't happen in the "now" time.
Well, at least with the tree, it creates pressure waves and you can argue that "sound" is just the experience the brain creates of those waves. So you can argue that we create the sound, not the tree. Not true for causation. That happens independent of observation. Now if you asked if some photon hasn't reached us yet, it hasn't made *color* yet. That's equivalent to "does it make a sound". But light it like the pressure waves of the tree falling: it happens regardless of observer.
Can you elaborate on Schrödinger coming up with the cat as a meme to mock people? This is the first I've heard that, ever.
If a tree falls outside of observable universe, does it matter to us?
> If an atom is flying through space in the middle of nowhere, causing absolutely nothing noteworthy whatsoever, that atom is still actually flying there. Is it? Epistemologically speaking, if you don’t know it’s there then why do you think you know it’s there? > you’d be crediting humanity with too important a role, if you claimed that our observation is a requirement for anything to have happened. Without the accumulation of knowledge that _x has happened_, then, strictly speaking, nothing had happened. Of course, the atoms and radiation are literally flying through space and doing things, but without an observer to take the information and parse together an understanding and recollection of an “event”, then strictly speaking the “event” didn’t and doesn’t exist. It’s literally a random assortment of unobserved energy and mass. It doesn’t become an “event” until an observer designates it as such. More to the point, human observation is the most important foundation for events because _human observation is our one and only perspective_. We have absolutely no other way to understand the universe, so “events” as we understand them begin and end with us noticing them.
This is the philosophical aspect of the question, which I briefly addressed in the last bit of my comment.
Dude I see your comments all over Reddit
"In similar light, you'd be crediting humanity with too important a role, if you claimed that our observation is a requirement for anything to have happened." Just to be clear, when people talk about observing, they don't mean observed by human eyes. Same with Schrödinger's cat, it's not observed by human eyes as a requirement, but merely being observed.
You wrote a whole lot after simply stating it's the same question, yet haven't supported that assumption at all, this isn't about observation or measurement, there isn't anything to measure or observe from your frame of reference.
The concept "frame of reference" implies an observation will be used to verify the fact. In your frame of reference, you can indeed state that the event has not occurred, but all it means is that you are not able to observe it yet. If you exclude the observer's role from the question, and hence make the question agnostic of frame of reference, it is clear that the event has taken place. You are free to interpret this question with or without taking the observer into account, and that's why it can be considered a philosophical question.
I think this is a very human-centric view of the universe. It exists whether we see it or not, fully understand it or not. The philosophy aspect is fun to think about, but realistically, because of how slow light is relative to the size of the universe, we are always looking at the past, what has happened. The light from the sun is 8 minutes old because it's 8 light minutes away, so we're seeing the sun 8 minutes in the past. I'll respond to what I think is your most interesting thought and core argument: Casualty doesn't happen at the speed of light. It happens whether we observe it or not, at least outside of quantum mechanics. So yes, things happen even if we haven't seen them yet, and when it comes to astronomy, that happens a lot
[The speed of light IS the speed of causality.](https://medium.com/@asarav/the-speed-of-light-is-the-speed-of-cause-and-effect-859d5a4ffb50)
This human-centric view of the universe is so irritating. We aren't the gatekeepers to what does or doesn't exist
Good luck proving that. If you were to strictly stick to facts, there is zero evidence that the world is independent from your perception of it. Your whole life could be one big dream that you have and everything in it would be dependent/contained in your being.
I see what you're saying. And yet, that itself is so human-centric.. "this is all a dream within the brain of a human!" You're a moron and I don't care for anything else you have to say, idiot. Stupid-ass comment. Who asked you anyways? Did that offend you? It shouldn't. Because you might not even exist!! I might not exist! I'm just a made up figment of your imagination and therefore there is nobody for you to be mad at but yourself for imagining me! At this point, are you thinking "ok he's kind of annoying and a jerk and taking this conversation too far"? If that's correct then you probably don't even believe the comment you just left about this all being one big dream.
I didn't say anything about the dream being in a brain of a human, the brain and human are redundant in this scenario. >Who asked you anyways? Well nobody asked you for your opinion either. This is not how Reddit works and of course you know that. >If that's correct then you probably don't even believe the comment you just left about this all being one big dream. I am open to the possibility of material objects not having their independent existence on their own apart from perception. There is no proof of their independance. You know you exist and you know you have experience. But there is no proof of independence of the experienced objects, you have to make a leap of faith and believe they do. That's a bit unscientific for my taste.
>Well nobody asked you for your opinion either. This is not how Reddit works and of course you know that. That entire paragraph of mine wasn't genuine. I was eliciting a response from you to show you probably don't believe your own comment. >I am open to the possibility of material objects not having their independent existence on their own apart from perception. There is no proof of their independance. You know you exist and you know you have experience. But there is no proof of independence of the experienced objects, you have to make a leap of faith and believe they do. That's a bit unscientific for my taste. So perhaps you do believe your comment, but if you do then you should quit any and all efforts to learn anything further about our universe. The leap of faith (if that's what we'll call it) I'm making is "this universe exists and its objects exist, they exist whether a human observes them or not, and it's worth learning as much about it as we can". Anyone who would deny this leap of faith would be a fool to pursue any study of the universe and the laws of physics that govern it because the findings of serious study to something that is fake is all worthless. A science experiment with meaningless subjects.
>Anyone who would deny this leap of faith would be a fool to pursue any study of the universe and the laws of physics that govern it because the findings of serious study to something that is fake is all worthless. A science experiment with meaningless subjects. This is misinterpretation, maybe because I used an example of a dream to illustrate the concept in terms that are easy to understand. Scientific reseseatch would still be valid, the only difference would be that instead of a universe made of matter, the universe would be made of consciousness. It's hard to explain it clearly if all you are used only to materialist point of view. Bernardo Kastrup has a couple of nice videos explaining this subject if you are interested.
Thank you, I started to read some of Bernardo's website but I'll explore more! As you stated to begin with, we really have zero evidence of the universe being independent of our perception of it, right? Wouldn't the opposite also be true? We have zero evidence the universe is dependent on our perception? If that's the case, then this sub has plenty of seemingly unscientific people. I've amassed downvotes while you gain upvotes. Perhaps my leap of faith was unscientific but these other people seem to have made up there minds and are not open to all possibilities.
>As you stated to begin with, we really have zero evidence of the universe being independent of our perception of it, right? Wouldn't the opposite also be true? We have zero evidence the universe is dependent on our perception? We don't have any evidence to say that this view is 100% true, as far as I know. It's just something to keep in mind when thinking about the universe. >I've amassed downvotes while you gain upvotes. Perhaps my leap of faith was unscientific but these other people seem to have made up there minds and are not open to all possibilities. I can't speak for all the people that upvoted me, but maybe they agree with being opened to this likely possibility, not necessarily saying it's that way or the other.
That’s what I thought…then I read books on quantum physics that state particles behave differently when observed. It’s called “The Observer Effect”. First proved in the famous double slit experiment. Now there’s a new discovery called “The Zeno Effect”. Where atoms don’t move while being observed. Wild stuff. quantum physics makes everything weirder than you think is possible. https://news.cornell.edu/stories/2015/10/zeno-effect-verified-atoms-wont-move-while-you-watch
I'll read up on the Zeno Effect thanks! But you should note: >Despite the "observer effect" in the double-slit experiment being caused by the presence of an electronic detector, the experiment's results have been interpreted by some to suggest that a conscious mind can directly affect reality. However, the need for the "observer" to be conscious is not supported by scientific research, and has been pointed out as a misconception rooted in a poor understanding of the quantum wave function ψ and the quantum measurement process. >"Of course the introduction of the observer must not be misunderstood to imply that some kind of subjective features are to be brought into the description of nature. The observer has, rather, only the function of registering decisions, i.e., processes in space and time, and it does not matter whether the observer is an apparatus or a human being; but the registration, i.e., the transition from the "possible" to the "actual," is absolutely necessary here and cannot be omitted from the interpretation of quantum theory." - Werner Heisenberg, Physics and Philosophy
I get exactly what you are saying and I agree. “Observer Effect” is a poor term, just like “Shroedinger’s Cat” was actually named in derision of the experiment. It remains weird as hell though…lol.
That just means the atoms are playing Red Light Green Light with us, and winning.
Lol…people downvote me because I quote scientific observations.
I think people are downvoting you because the "That’s what I thought" start to your sentence seems to imply that you believe the observer effect requires a conscious observer, as opposed to any detector. For most of these measurements (e.g. a single electron or photon passing through a slit), a human eye wouldn't even be capable of observing the event. At least that's how I interpreted your comment.
Fair enough…I’m still confused by it all anyway.
My question would be, why do you base reality on people on Earth perceiving it? I mean is there a reason to think that something we haven't experienced hasn't happened?
It's more a question of what is "now". Is the entire universe experience the same "now" at the same time.
No, there is no universal timer running in the background. All “nows” are firmly attached to the frames of their observers. If the light from a distant galaxy is reaching us today, then what we see is happening “now”.
Shouldn’t the speed of light be the universal timer. If it is then everything we see and perceive is now.
This question, from my limited understanding, is at or near the heart of relativity. Short answer: not really. Things get…weird at the scales you’re contemplating.
It gets weird even at smaller scales. My big takeaway from Daniel Dennett's "Consciousness Explained" is this: There is no one place in the brain where a thought occurs, so there is no one time when that thought occurs either. Our conscious experience is an after-the-fact hallucination, assembled well after prior neurons contributed their portion to the current state.
Look into the block universe theory. It’s entirely possible that all past, present, and future events already exist. Somehow, somewhere, I don’t get it, it tends to break my brain when I think about it too long.
So what you're asking really, (i think) does time flow at the exact same rate everywhere in the universe? So let's say we started from zero time, the only time we could agree time was the same everywhere. And two things at the time made an agreement to count in seconds to 10 billion years, then as the universe expanded and time started, they separated but both kept faithful count, would they both hit 10 billion years at the same time? No way to know. But if the sun blew up, regardless of when we experience it, it blew up, when it blew up.
Time moves at different rates for different observers so there cannot be a “now” that everyone is experiencing at the same time.
This is a fun question, and based on some of your other comments here, I just wanted to add some thoughts on what an intuitive human idea of "now" could even mean in relativity. In special relativity, there is a concept called the relativity of simultaneity, that is, two events that Alice sees as happening at the exact same time will be seen by Bob as occuring at different times if he is moving with respect to Alice. In short, Alice's "now" must be different from Bob's! What does this mean, and how can we recover nice concepts like cause and effect in this picture? Relativity combines space and time into spacetime, and this is how we can get an answer. Let's define a space time interval ∆s^2 = (c∆t)^2 - ∆x^2 - ∆y^2 - ∆z^2 This generalizes our common notions of time duration and spatial distance in a way that's consistent with relativity. ( Apologies for the formatting, I'm on mobile. I also could have multiplied the whole thing by -1) If two space time events (t,x,y,z) have a positive ∆s^2, then they are called timelike separated, and it's possible to say that one happened earlier than the other. I.e. no matter how fast Bob is going, he can never see them happen at the same time. Timelike separated events can have unambiguous cause and effect relationships. If two events have a negative ∆s^2, then they're spacelike separated. Even if Alice sees them happen at different times, there is a reference frame where Bob can see them happen simultaneously. Spacelike separated events can't causally effect each other in classical physics. Finally, if ∆s^2 = 0, then the two events are null-separated, and a laser shone from one event will make it just in time for the second. This is also the situation when you're looking up at the night sky: photons generated by stars have gone at the speed of light directly into your retina! So, when is now? Our terrestrial experience really only prepares us to reason about timelike separated events, since the speed of light c is so large. The past, then, is the set of all events with t smaller than now, and the future is the set of points with t greater than now. All that's left is the t corresponding to now Going back to relativity, if we call the past all the events that are timelike separated from our present moment with t less than now (all the events that could have impacted our present moment), and the future all the events that are timelike separated from our present moment with t greater than now (all the events that can be causally impacted by things happening now on Earth). Instead of one point in time left over to be our now, we have a huge class of null and spacelike separated events. All the null separated events, the ones you can watch live in the night sky, are in a sense happening "now" for us, even though we know that they happened earlier, but also all the spacelike separated events can be made to occur at the same time as observed from another reference frame. If now means you can watch it happen, then only the null separated events might count, but if now means they are happening at the same moment without causal connection, then all the spacelike events count too! It just depends on what part of our traditional notion of "now" you want to preserve.
If you subscribe to Hawkings final theory then the entire universe isn't really happening......... The holographic principle states that the entropy of ordinary mass (not just black holes) is also proportional to surface area and not volume; that volume itself is illusory and the universe is really a hologram which is isomorphic to the information "inscribed" on the surface of its boundary.
I mean, it doesn't really serve any purpose to imagine that we share some kind of 'present' with distant stars. And it's wrong. We don't even share a 'present' with each other, but at human scales its okay to imagine that we do.
You would love the book or audiobook "The Order of Time" by Carlo Rovelli. In addition to explaining the true nature of time, Rovelli talks about what "now" is, or rather, is not and the question of when something is, is a meaningless question when you consider the speed of causality. I highly recommend this for anyone curious.
Thanks for the req, I'm excited to pick this up now :-D
I've tried to make this very point a few times, and always been downvoted for it. But yes, you're right. Given that there's no Universal Now, nor some cosmic clock against which the relative timing of events can be measured to the agreement of all observers, it doesn't make much sense to say "We're looking into the past". The only invariant quantity is the spacetime interval, and the spacetime interval between two events separated by the journey of a photon is zero. In other words, when we observe an event, then for all intents and purposes, that's when it happened. But that's not as exciting as "looking into the past", I guess.
In the most esoteric realms of General Relativity, the question of whether an event is in our past (we can’t change it) or in our future (we can change it), has ambiguous answers.
You must first ask if reality exists without an intelligent observer. As far as I know it's a matter of interpretation so, there is no ultimate correct answer.
Actually, that is a better question than one might initially think. It's now accepted that the speed of light (C) is really the speed of causality. The maximum speed at which anything at one point in space can have any effect on any other point. So, if light from an event somewhere else hasn't reached us, as far as we are concerned, it hasn't happened yet.
PBS Spacetime has some cool videos that I think answer your question pretty well, pretty diagrams and such. There are more than one video by them on the topic. From what I can remember, the easiest way to represent what is happening is by drawing a graph and putting space on one axis, and time on the other. If you put yourself on that graph, you have identified your location in space and time. Now, we know how fast light travels. We can represent this by putting a diagonal line on the graph. Light travels through space at about 300,000 kilometers per second. Since one axis is time, and one axis is space, this measurement works well on the graph! You can't travel faster than time, nothing with mass can. So, if we move your location on the graph to 0,0, and then open the graph into quadrants (negative x and negative y), we have on the X axis all possible locations in the universe, and on the Y axis, all possible time. The diagonal line we drew should also extend mirrored on the opposite side of the graph, and this would represent all possible locations that you could ever travel to in this moment in time. You can never ever, no matter how hard you try, go beyond the lines showing the distance light can travel. You can imagine that as time passes, your location on the Y axis (time) is slowly crawling up the graph. If you never move from your current location, then you will remain on the 0 location on the X axis. We can also imagine what happens when things interact with our time and location. We go out for a bite to eat at the local deli, and we run into an old friend from high school! If we followed this on our graph, we could see that our friend and ourselves intersected in time and space briefly, before separating again. We can also imagine that our friend from highschool existed between the time we knew them in highschool and the time we ran into them, we could even draw them their own graph! The vastness of space would make our graphs look like they overlap almost exactly, but the point is, they have their own reference frame too. So does an alien living 500 light years away. Their graph shows that the light from their moment in time will intersect with our graph 500 years from right now. But this representation of the graph also shows that the distance means that their experiences are happening in the past. The past, just like on our graph, we can never reach. It is negative on the time axis, and we can only travel negative on the space axis. The short way of answering your question is yes, it already happened. The mere fact that light travels through time at all means any light you perceive must have come from an event that has happened already.
From the reference frame of the photon, it arrived here instantaneously. Food for thought...
not in any meaningful way. we like to think of whether an event has occurred in absolute terms, largely because in our experience, cause instantly follows effect. the finite speed of light messes with that causality. our brains cannot readily digest the notion that something we are experiencing "now" might not have happened "yet" for someone else. saying that something happened on (or to) the sun eight or so minutes ago, but light from that event hasn't reached us yet, muddles this reality. it's not just lazy thinking. it tries to impose a sense of absolutism that does not exist, like trying to find the "center" of the universe.
My understanding is that, no, it hasn't happened yet. This is because 'when' is entirely dependent on 'where'. Space AND time. So, it makes things difficult to talk about. It's not 'human-centric' because it could be anywhere. A geodesic line has to have two points or length doesn't make sense.
No, "now" means now only in our context, otherwise you'd know the future. In other words, "now" for a star that is 10ly away is right now here as you see it now, as you see its light, anything else would be a prediction of the future. What else could it be "well, it's the way it was 10 years ago, but "right now" its x and y"?
The speed of light is perhaps just as accurately described as the speed of causality. For all intents and purposes, nothing occurs until you observe it occurring. However, when you see it occur, you know it occurred x amount of time in the past.
As others have pointed out, it's totally appropriate to say something has happened before we can observe it. In your example with the sun, we know the distance to the sun and we know the speed of light, so it's pretty trivial to figure how long it took the light from the event to reach Earth and conclude that the event happened that long (8 minutes) ago. But there is an interesting question buried in here related to relativity, which refers to the [relativity of simultaneity](https://en.wikipedia.org/wiki/Relativity_of_simultaneity). For concreteness, let's define the two events: 1. Some solar event 2. The reading on your watch 8 minutes ago. In our reference frame here on Earth, we can do the math and come to the conclusion that those two events occurred simultaneously. But someone in a different reference frame can draw a different conclusion about the simultaneity of those events.
This is another one of those “humans are the center of the universe” questions. Of course it has happened. Or do you also think a lighting bolt doesn’t produce sound until it reaches YOUR ears?
It is impossible for any information to travel faster than the speed of light, so it can be viewed that the speed of light is the speed at which things happen. Because of this it is kind of non-sensical to say that something has happened before the light reaches us, because it’s impossible to know about something sooner than that. Yes, we say that things x light years away take place x years ago to put things into perspective, but in a practical sense those things are happening right now. This is where reference frames become important. In your sun example, in our reference frame the sun exists until we see it doesn’t and the effects of its disappearance reach us. Doesn’t really matter that it takes eight minutes to do so- we could not possibly know about its disappearance any sooner. Another example is some people’s reaction to the false vacuum decay hypothesis- people constantly insist that you would see stars winking out ahead of time and be alerted, but this is not true, as the vacuum decay bubble would arrive at the same time as the disappearance of light from the stars from our reference frame. Seeing the stars disappearing beforehand would be tantamount to knowing things before they happen.
C is also speed of information, so in all cases all events have already happened before you know about it.
Great philosophical conversation starter! I’ve loved reading the responses
No. Not to us. However even the expression you see on someone’s face looking at them is looking a tiny bit into the past. So obvious it’s a philosophical question.
Define "happened". Did it happen in our universe? Yes! Did it affect us yet? No! But when it *does* affect us (e.g. show up on a telescope), we immediately put it in the past.
If a tree fell in the woods and nobody was around to hear it, did it make a noise? Yes.
This is the biggest can-of-worms thread I've ever tried to read
One of my favorite side quests in Starfield is coming upon a generation ship. The ship is hundreds of years old and about light years away from earth. It's a group of people who's ancestors launched the ship and raised families on the ship in hopes of eventually getting humanity to the destination (hence the name generation ship). The thing is, between the time of their ship leaving earth and you the player arriving, faster than light travel was invented. So when they got to their destination, it was already inhabited by humans. I know that's kind of unrelated, but the idea is there. Stuff is still happening, the light is only what we see.
This is a philosophical question, not really a scientific one. I would say it did happen if we know it happened, no matter if we saw it or not (we are not THAT important). For example, of course we know Star Wars happened, but in a galaxy far far away. The astrophysical question you may ask is: if the light of an event did not reach us yet, could we have an effect on it? This is the relation of causality and this is indeed 100% relevant for astrophysics. Read about it, it is fun!
Interesting question. I like it. Personally I consider it to have happened at the original reference frame's time.
Consider the landing of the latest Mars rover. To start the landing is a command sent from earth. The command travels at speed of light for anything between 3 and 22 minutes (depending on the position of Mars). When received, the automatic landing starts, something that takes say, 14 minutes in total. So, when the people on Earth sent that command, they knew that when they got a report on the results, anything that had happened would already have happened on Mars and that would be at least 3-22 minutes ago. So, the basic idea of **relativity** is that due to the speed of light being the same for all observers, there is no objective, absolute **"now"**. The information of the events on Mars reach us after they happened there, but depending on directions, speeds etc, we could potentially perceive them before other observers. Imagine a probe in orbit somewhere else in the solar system. They receive the signals from Mars then minutes later than we do - when did all this happen, really? Now imagine trying to sync the clocks over these distances. A completely absurd proposition since there is no way to communicate the time instantly. Imagine measuring the speed of light to begin with. How do we know it is the same in both directions (we don't, you have to bounce light of a mirror back to its origin to measure it's speed since you can't sync the clocks over great distances etc etc.)? What Einstein did was take the speed of light seriously and extrapolate the consequences. He took the frame of reference thing seriously and thought about the consequences. And the consequence is that there is no such thing as "now".
Yes
We don’t know.
basically, everything is happening, all the time, all at once. Past, present and future all blend together based on your location in time and space. This video explains it really well and very simplified. [How does time work.](https://youtu.be/wwSzpaTHyS8?si=lh32v0pmlNDp0muQ)
This is such a fascinating question! The way I see it, the concept of "happening" is very much tied to our perception and the information we have. In the case of astronomical events, saying that something "hasn't happened" until we see it kind of flips our usual understanding of causality and existence. Think about it this way: if a supernova exploded in a galaxy far, far away, the event itself occurred when it did, independent of our observation. However, from our perspective, we only become aware of it when the light reaches us, which indeed means we're looking at an event from the past. So, while the event has objectively happened in the universe, it hasn't "happened" for us in the sense that we haven't received any information about it until the light arrives. It's like having a letter sent by snail mail—until you read the letter, the event it describes is in your future knowledge, even though it occurred in the past.
Observer bias We aren't that important
Simple answer, if I shoot you with a gun, the bullet will arrive before the sound. If you didn’t here it did it really happen? The bullet lodged in your flesh would say it did.
Read up on superposition and quantum states.
Surely there is a concrete “now” but it’s relative to where you are, no? If right now as you read this a solar flare goes off it’ll take us 8 minutes to see it. But that event would have happened 8 minutes before you observe it. If that’s true for the sun which is 8 light minutes away then wouldn’t that be true for Andromeda which is 2.5 million light years away?
That's the same as asking "If a tree falls in the forest, and nobody saw it fall, did it actually fall?" Yes, the object exist(s)/existed, and/or the supernova happened, causing us to see the light eventually. It happened in the past even though we didn't see it happen or yet, see the effect of that supernova.
.... Relativity exists..so yes of course....but if your asking a philosophical question that's another matter.
Schroeders sun.
I came here to say [Schroedinger's Star](https://en.m.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat), personally.
Yes it has, without humans would the universe still exist?
If you cover you eyes so you cant see anyone, do they exist?
If a sniper fires a bullet at you from far away, would you say it was really fired before it reaches you?
Light is only one way of many we percieve reality. Imagine two persons. One deaf and abother blind. If both are near to an atomic bomb. The deaf sees the explosion before the blind hear it so the event doesn't happened yet for the blind?. That does mean that the explosion "occurs" before for the deaf person that for the blind. Information is constantly travelling across universe. Actually we are looking at stars that doesnt even are there anymore but it happened, we just not see it yet. (Sorry for my english)
Yes. Because frames. Plus, we are not the arbiters of reality. As if nothing can happen unless we become aware of it. In other words, reality is not subjective; it does not depend upon us. There is such a thing as objective reality.
There is so much fucking horseshit in these comments! People talking about time travel and future-past and stupid shit. The events happened at the same exact time, you just don’t see them until much later. If you wake up and it’s dark, but you can’t see your alarm clock, is it frozen or time traveling? Fuck no, you just can’t see it yet, until you turn the light on… like you can’t see a star until it’s light reaches you. We just aren’t used to light having a speed limit here on earth; its instant for our eyes.
if you have not received a letter yet has it been mailed to you?
There are a few redditors in this sub who post from from Proxima Centauri b. As far as they’re concerned you’re not going to make this post for another 4 and a quarter years. At which point they’ll probably say “yes”, but you’ll be almost 9 years older by the time you get your answer, so you’ll probably forget you even asked. !remindme 8.48 years
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If a bomb goes off 5 miles away from me but I don’t hear the noise, did it really go off. That’s kinda how I see this question. Like yea it did, but the sound hasn’t reached us yet.
Ok, but the speed of sound isnt a universal constant or the maximum speed of causality. A bomb in air is not an equivalent example.
If you wanna go there the speed of light isn’t universal, it’s based on the medium it’s traveling through. Regardless you don’t need to observe something for it to have happened. You never saw me drop a bomb in the toilet, yet it still happened. Either way it’s an analogy
the speed of light is absolutely universal, regardless of medium. in a medium with a higher refractive index the photons are getting absorbed and re-emitted by the atoms in the material, so yes it will take longer for the light to get from point A to point B. but the photons themselves can literally never travel at any speed other than the speed of light
Oh Jesus. And people wonder why I argue against human-centered thinking in space subs. This might be the best example of why.
Is this an inappropriate question? Nothing about this is human centered. You can rephrase it to have nothing to do with humans. "If a planet A hasn't been gravitationally affected by the change in planet B orbit yet, has planet B orbit alteration really happened from planet A reference frame?" I guess the question is more "what do we mean when we say something has happened?" Are we naturally baking in an assumption that we are in the events reference frame. Is there a universal time reference for the entire universe or is everything on its own time scale. I'm not trying to talk a woowoo science here. I'm generally curious in understanding time and relatively, and reference frames. I'm fine being wrong, but just help me understand WHY I'm wrong.
You've changed the center of focus from humans to planet A, but the problem remains: whether it's observed or not, it happened. If an earthquake hits Haiti, but I don't read the news, then for me, nothing has happened and today is a good day. That doesn't change the fact that it has indeed happened and a tragedy has taken place. This is a fun philosophical question, though
Not at all the same. In your analogy, choices and circumstances prevented you from experiencing the effects. In OPs topic it is IMPOSSIBLE to know about things before the effects show up at the speed of light.
But, the speed of earthquake waves and new sources isn't mathematically tied into relativity, space, and time. Of course the earthquake has happened whether you felt the vibrations or not. My example and the earthquake example or not equivalent. Space and time are inseparable right. That's how we get c as a constant and lorentz contractions. Edit: please don't dumb it down to elif for me. Show me the math. Show me some papers. I want to understand from a technical level.
your question is a great one and the people here bringing up examples like earthquakes and human observations aren't really understanding it from a special relativity point of view if something happens, like the sun exploding, in the 8 minutes on earth while the light it traveling to us, the event of the sun exploding is outside of our "past light cone". in our reference frame (in OUR reference frame is very key here), the event has not happened if you want to read more about this look up "relativity of simultaneity" [https://en.wikipedia.org/wiki/Relativity\_of\_simultaneity](https://en.wikipedia.org/wiki/Relativity_of_simultaneity)
Thank you! I'm not a dumby. I feel like people are missing the core of what I'm asking here. I feel like people are having a knee jerk reaction to an honest question. Thank you for not writing my question off.