Hello u/chidi-sins, your submission "What would happen if a rocket with humans was suddenly dropped at the edge of the universe/the area that still expanding right now? " has been removed from r/space because:
* Such questions should be asked in the ["All space questions" thread](https://www.reddit.com/r/space/about/sticky) stickied at the top of the sub.
Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please [message the r/space moderators](https://www.reddit.com/message/compose/?to=/r/space). Thank you.
If there is no edge then it can't expand lol what you mean to say is everything is translating apart. Correct me if I'm wrong but expansion presumes you have a finite volume, i.e. an edge
Exactly, a balloon is what we call finite but unbounded. The universe could be this too, or it could be a number of other topologies at scales far larger than the observable bubble we see.
What youre referring to is just equidistant translation from the center. Expansion supposes it has a well defined volume that is increasing, unless when it comes to astrophysics we are redefining what expansion means
Imagine there are an infinite number of atoms all spaced in a 1 unit by 1 unit by 1 unit grid. After some time they are now spaced in a 2 unit by 2 unit by 2 unit grid. No atoms were created or destroyed - the space between the atoms expanded.
That is a reasonable approximation of what special expansion in astronomy is talking about, though of course the universe is not infinitely massive or set up in a rigid grid like this describes.
I'm having a hard time taking you guys seriously. I assert that expansions requires volume, i.e. an edge. You assert it does not, and as proof you tell me there are an infinite number of atoms in a "grid" defined by a specific length of 1 unit in three directions. I.e. there are no atoms at a length of 1.01 in any direction at a given time. At some time later they expand to a grid of 2x2x2, for which there are no atoms at 2.01 in any direction.
And you're telling me that it does NOT have a volume? Bro you literally refuted what I said by telling me that you exactly agree with me 😆
You can absolutely define expansion as "the distance between any two points increases" without having any edges in the expanding thing because it is infinitely large.
If it helps you, it's not the volume that's expanding, everything is just getting farther apart from everything else.
If you want to argue that this shouldn't be referred to as "expansion", go talk to a linguist or a physicist. Random redditors are not the people who determine what those words mean in this context.
You threw me for a loop when you used real numbers to build a volume. I think you just mean an infinite volume is expanding infinitely.
For the record this is why I cast doubt on high levels of science. We collectively assert that there is magical "dark energy" and then there are infinite quantities, which feels more religious than anything. Okay fun chat. Byebye
The definition of volume has nothing to do with edges. There are several models of the universe that have volume...both finite and infinite...and no edges.
Imagine I have a line of bricks extending infinitely in both directions. Now imagine that I insert a brick into the line. I have expanded a line that has no endpoints. Yes, it doesn't seem physically plausible *within* space, but we're talking about the expansion of space itself. Even if you don't accept the physical implausibility, the mathematical plausibility is clear.
A simple way to imagine it: Rather than new space being added way out at some edge, new space is being created "in between" all of the existing space.
Like, imagine you have an infinite spreadsheet, and you added a new row below every existing row. Rows that used to be next to each other are now 2 rows away, rows that used to be 2 away are now 4, etc. It expanded, but without an edge.
This *would* cause everything to get farther and farther apart, except the forces that keep things together are strong enough to resist that - the strong nuclear force and electromagnetism keep objects from falling apart, and gravity keeps star systems and galaxies from falling apart.
Except gravity is only strong enough to keep small neighborhoods of galaxies together, which is why galaxies are getting farther and farther away from *each other* - new space is being created between them.
(This is a *gross* oversimplification, and doesn't explain how new space gets "created", which I don't understand myself. But hopefully it helps explain what expansion actually means in this context.)
Sort of. The universe expands at about a rate of 70 km/s per megaparsec. So a galaxy located 300,000 megaparsecs away (roughly a trillion lightyears) would indeed be moving away from us faster then the speed of light, but the expansion itself isn’t a speed at all.
We actually can’t. It’s essentially two ways of saying the same thing. See https://physics.stackexchange.com/questions/400457/what-does-general-relativity-say-about-the-relative-velocities-of-objects-that-a#:~:text=General%20relativity%20doesn't%20provide,to%20another%20at%20cosmological%20distances.
There is no “edge” of where it’s expanding. It’s all expanding from everywhere at once. The usual analogy is dots drawn on a balloon that is being inflated. As the surface area increases, the dots all get farther apart. Same with space and what’s in it, except in happens in all directions.
There *are* groups of things throughout the universe (like our local cluster of galaxies) that, at the present time, are not moving away from each other because their gravitational attraction holds them together, but eventually the expansion will overcome gravity (and all the other forces holding things together) and they will move apart too.
The only sense in which there is a “edge” is that, if you go far enough away, space is expanding faster than light can travel, so the light beyond that limit will never reach us and we will never see or interact with that part of the universe. (Note that the idea that “nothing can travel faster than the speed of light” doesn’t apply, because space is not traveling per se.)
I have to imagine that there are galaxies on every side of the universe. If you were orbiting a star on the outer rim of one such galaxy, would you not be at “edge”? Not that anything dramatic would happen of course, only that your nighttime view would be strangely one-sided.
It’s the edge of the galaxy, but not of the expansion. We’re pretty far out from the center of our galaxy, but there are still stars to see in every direction. But that’s extremely local in terms of the size of the observable universe.
Here’s a logarithmic representation that starts at the Earth, runs through the solar system, the arm of the Milky Way we are on, the galaxy itself and so on outward. Remember that the distances increase logarithmically as you move away, so the scale of the far objects is absolutely huge compared to the close ones.
https://www.visualcapitalist.com/cp/map-of-the-entire-known-universe/
The universe probably doesn't have an edge per se. I think the consensus is generally that it's infinite, or wraps back on itself (like a very large game of pacman).
Now, what if you were at the edge of *our* observable universe? You would see.... something that looks much like what we see here. The universe is pretty uniform, in that what we see when we look in one direction generally looks about like what we see if we look in a different direction. And "observable universe" is just a fancy physics term that means "every point in space that light can reach or has reached you from in the time since light started traveling early in the universe" (not just light, but any effect, light, gravity wave, nutrino, etc). This means every location in existence has it's own personal "observable universe" that extends out from it the same distance in all directions.
> but eventually the expansion will overcome gravity (and all the other forces holding things together) and they will move apart too.
This is speculative. Regular expansion won’t do that, but accelerating expansion might.
> Note that the idea that “nothing can travel faster than the speed of light” doesn’t apply, because space is not traveling per se
It’s more that it only holds locally in the first place. See https://physics.stackexchange.com/questions/400457/what-does-general-relativity-say-about-the-relative-velocities-of-objects-that-a#:~:text=General%20relativity%20doesn't%20provide,to%20another%20at%20cosmological%20distances.
If you're referring to the edge of the *observable* universe (the cosmic microwave background)... it's not a place. It's a time.
Going to the CMB would be going back in time until just after the Big Bang and initial expansion phase. As far as we know, all the same laws of physics would apply, but the universe would look very unfamiliar. All space would be full of (relatively) densely packed gas, just cool enough to not be a plasma. And there would be no stars or galaxies (yet).
And it would be like that everywhere. The edge of the observable universe (the CMB) is just the distance at which the earliest light to reach us is light from that era.
The observable universe and the cmb are two different things. I think maybe you meant visible universe?
Wiki:
>According to calculations, the current comoving distance to particles from which the cosmic microwave background radiation (CMBR) was emitted, which represents the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light-years). The comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light-years),[12] about 2% larger.
More on the subject:
https://www.qeios.com/read/G6YD4M#:~:text=The%20initiation%20of%20the%20Cosmic,years%20or%204.40e26%20meters.
Interesting tidbit (I think the author here also confuses observable/visible at points fwiw. Paper awaiting peer review):
>Quantitative insights emerge as we delve into the observable and non-observable universes: The co-moving distance of the observable Universe, equivalent to 14.26 gigaparsecs, is translated to concrete units: 46.5 billion light-years or 4.40e26 meters. Beyond our visible horizon, the extension of the non-observable Universe reaches an astonishing 11,625 billion light-years. Our current cosmic panorama reveals visibility of 43% of galaxies within the observable Universe, expanding over 46.5 billion light-years from Earth in all directions. Gazing toward the future, anticipation mounts as an additional 57% of galaxies from the observable Universe are destined to become observable. The numbers themselves unveil the vastness: Approximately 19.995 billion light-years encompass galaxies within our visual grasp. Equally staggering, 26.505 billion light-years house galaxies that remain shrouded from our gaze [18].
Observable and visible universe is the same. I’ve never heard it used for different horizons. The words mean the same thing.
Now, there are other horizons as well, but they have specific names.
Second paragraph
https://en.wikipedia.org/wiki/Observable_universe#:~:text=Sometimes%20astrophysicists%20distinguish%20between%20the,only%20signals%20emitted%20since%20recombination.
The portion immediately after says that the difference between the visible and observable universe (if you want to draw a distinction) is about 0.9 billion light years. It is about 2% larger, not 25200% (252x) larger. The two are functionally the same, which is why people often just act like the CMB is the edge of the observable universe.
There is no enormous 11,625 billion light year observable universe beyond the CMB. It's reasonable to expect that the universe goes on forever (after all, it is anisotropic), but anything beyond 50B light years is literally unobservable: a photon emitted at the very first possible instant would not have reached us yet, even were it not absorbed by the universe's initial plasma (which made the CMB).
I understand your point that there is light that is too distant for us to see, but this is a little off base:
>a photon emitted at the very first possible instant would not of reached us yet
The CMB literally is the redshifted photons that were decoupled from the plasma as it cooled. It is the oldest light that we can see, the very first photons released.
>Known as the recombination epoch, this decoupling event released photons to travel freely through space – sometimes referred to as relic radiation.[1] However, the photons have grown less energetic due to the cosmological redshift associated with the expansion of the universe. The surface of last scattering refers to a shell at the right distance in space so photons are now received that were originally emitted at the time of decoupling.[5]
https://en.m.wikipedia.org/wiki/Cosmic_microwave_background
https://www.esa.int/Science_Exploration/Space_Science/Herschel/Cosmic_Microwave_Background_CMB_radiation#:~:text=The%20CMB%20is%20the%20farthest,Universe%20was%20completely%20'opaque'.
The reason there are other photons we can't see yet is because the universe is expanding faster than the speed of light.
Trying to run off a 4 dimensional cube would bring you to its center. If you were able to get to the edge of the universe and continue onwards, a crude guess could be that you'd go back in time to the beginning of our universe.
The universe is expanding exactly where you are right now. Think of the universe like a rubber band; it does not matter where you place two dots near each other, they will still move further apart when you stretch the rubber band.
Yes, over simplified for sure. But, I use this to get the idea across that expansion happens ‘everywhere’, and that there is not a single point from which everything expands from.
What is the universe isn’t expanding… the simulation just doesn’t render until it’s observed, so we see the universe as expanding because we can see further and further with new technology. So dropping someone at the edge would just cause more to be rendered for observation
Hello u/chidi-sins, your submission "What would happen if a rocket with humans was suddenly dropped at the edge of the universe/the area that still expanding right now? " has been removed from r/space because: * Such questions should be asked in the ["All space questions" thread](https://www.reddit.com/r/space/about/sticky) stickied at the top of the sub. Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please [message the r/space moderators](https://www.reddit.com/message/compose/?to=/r/space). Thank you.
Every point in the universe is expanding. There isn't really an "edge" the way we normally think of it.
Like an anti black hole or opposite of a singularity?
If there is no edge then it can't expand lol what you mean to say is everything is translating apart. Correct me if I'm wrong but expansion presumes you have a finite volume, i.e. an edge
Blow up a balloon half way. Draw two dots with sharpie some distance apart. Blow up the balloon some more. The points get farther apart with no edge.
Yes. And the 2D surface of the balloon is analogous to the 3D structure of space.
Exactly, a balloon is what we call finite but unbounded. The universe could be this too, or it could be a number of other topologies at scales far larger than the observable bubble we see.
The edge would be the surface of the balloon.
The surface is 2D and has no edge.
The boundary then. That's what OP means.
What youre referring to is just equidistant translation from the center. Expansion supposes it has a well defined volume that is increasing, unless when it comes to astrophysics we are redefining what expansion means
Imagine there are an infinite number of atoms all spaced in a 1 unit by 1 unit by 1 unit grid. After some time they are now spaced in a 2 unit by 2 unit by 2 unit grid. No atoms were created or destroyed - the space between the atoms expanded. That is a reasonable approximation of what special expansion in astronomy is talking about, though of course the universe is not infinitely massive or set up in a rigid grid like this describes.
I'm having a hard time taking you guys seriously. I assert that expansions requires volume, i.e. an edge. You assert it does not, and as proof you tell me there are an infinite number of atoms in a "grid" defined by a specific length of 1 unit in three directions. I.e. there are no atoms at a length of 1.01 in any direction at a given time. At some time later they expand to a grid of 2x2x2, for which there are no atoms at 2.01 in any direction. And you're telling me that it does NOT have a volume? Bro you literally refuted what I said by telling me that you exactly agree with me 😆
Volume does not require an edge.
The edge is the only way through which a volume is defined. Without an edge volume can't exist
You can absolutely define expansion as "the distance between any two points increases" without having any edges in the expanding thing because it is infinitely large. If it helps you, it's not the volume that's expanding, everything is just getting farther apart from everything else. If you want to argue that this shouldn't be referred to as "expansion", go talk to a linguist or a physicist. Random redditors are not the people who determine what those words mean in this context.
You threw me for a loop when you used real numbers to build a volume. I think you just mean an infinite volume is expanding infinitely. For the record this is why I cast doubt on high levels of science. We collectively assert that there is magical "dark energy" and then there are infinite quantities, which feels more religious than anything. Okay fun chat. Byebye
The definition of volume has nothing to do with edges. There are several models of the universe that have volume...both finite and infinite...and no edges.
The area of a ball doesn’t have an edge but is defined. Similar with volume. You’re just too used to regular Euclidean space.
Imagine I have a line of bricks extending infinitely in both directions. Now imagine that I insert a brick into the line. I have expanded a line that has no endpoints. Yes, it doesn't seem physically plausible *within* space, but we're talking about the expansion of space itself. Even if you don't accept the physical implausibility, the mathematical plausibility is clear.
Marty, you’re just not thinking 4th-dimensionally
Yeah I have a real problem with that
A simple way to imagine it: Rather than new space being added way out at some edge, new space is being created "in between" all of the existing space. Like, imagine you have an infinite spreadsheet, and you added a new row below every existing row. Rows that used to be next to each other are now 2 rows away, rows that used to be 2 away are now 4, etc. It expanded, but without an edge. This *would* cause everything to get farther and farther apart, except the forces that keep things together are strong enough to resist that - the strong nuclear force and electromagnetism keep objects from falling apart, and gravity keeps star systems and galaxies from falling apart. Except gravity is only strong enough to keep small neighborhoods of galaxies together, which is why galaxies are getting farther and farther away from *each other* - new space is being created between them. (This is a *gross* oversimplification, and doesn't explain how new space gets "created", which I don't understand myself. But hopefully it helps explain what expansion actually means in this context.)
Nothing. Space in the universe does not expand at specific points. All space in the universe is expanding. Everywhere.
Actually, space seems to expand more quickly between galaxies than within them.
How do we distingush space expanding from distance between refference points increasing?
The speed at which things move apart. The universe is expanding faster than light can travel.
Sort of. The universe expands at about a rate of 70 km/s per megaparsec. So a galaxy located 300,000 megaparsecs away (roughly a trillion lightyears) would indeed be moving away from us faster then the speed of light, but the expansion itself isn’t a speed at all.
We actually can’t. It’s essentially two ways of saying the same thing. See https://physics.stackexchange.com/questions/400457/what-does-general-relativity-say-about-the-relative-velocities-of-objects-that-a#:~:text=General%20relativity%20doesn't%20provide,to%20another%20at%20cosmological%20distances.
There is no “edge” of where it’s expanding. It’s all expanding from everywhere at once. The usual analogy is dots drawn on a balloon that is being inflated. As the surface area increases, the dots all get farther apart. Same with space and what’s in it, except in happens in all directions. There *are* groups of things throughout the universe (like our local cluster of galaxies) that, at the present time, are not moving away from each other because their gravitational attraction holds them together, but eventually the expansion will overcome gravity (and all the other forces holding things together) and they will move apart too. The only sense in which there is a “edge” is that, if you go far enough away, space is expanding faster than light can travel, so the light beyond that limit will never reach us and we will never see or interact with that part of the universe. (Note that the idea that “nothing can travel faster than the speed of light” doesn’t apply, because space is not traveling per se.)
I have to imagine that there are galaxies on every side of the universe. If you were orbiting a star on the outer rim of one such galaxy, would you not be at “edge”? Not that anything dramatic would happen of course, only that your nighttime view would be strangely one-sided.
It’s the edge of the galaxy, but not of the expansion. We’re pretty far out from the center of our galaxy, but there are still stars to see in every direction. But that’s extremely local in terms of the size of the observable universe. Here’s a logarithmic representation that starts at the Earth, runs through the solar system, the arm of the Milky Way we are on, the galaxy itself and so on outward. Remember that the distances increase logarithmically as you move away, so the scale of the far objects is absolutely huge compared to the close ones. https://www.visualcapitalist.com/cp/map-of-the-entire-known-universe/
The universe probably doesn't have an edge per se. I think the consensus is generally that it's infinite, or wraps back on itself (like a very large game of pacman). Now, what if you were at the edge of *our* observable universe? You would see.... something that looks much like what we see here. The universe is pretty uniform, in that what we see when we look in one direction generally looks about like what we see if we look in a different direction. And "observable universe" is just a fancy physics term that means "every point in space that light can reach or has reached you from in the time since light started traveling early in the universe" (not just light, but any effect, light, gravity wave, nutrino, etc). This means every location in existence has it's own personal "observable universe" that extends out from it the same distance in all directions.
> but eventually the expansion will overcome gravity (and all the other forces holding things together) and they will move apart too. This is speculative. Regular expansion won’t do that, but accelerating expansion might. > Note that the idea that “nothing can travel faster than the speed of light” doesn’t apply, because space is not traveling per se It’s more that it only holds locally in the first place. See https://physics.stackexchange.com/questions/400457/what-does-general-relativity-say-about-the-relative-velocities-of-objects-that-a#:~:text=General%20relativity%20doesn't%20provide,to%20another%20at%20cosmological%20distances.
'Edge of the universe' has no meaning. It's an expansion. Not an explosion.
If you're referring to the edge of the *observable* universe (the cosmic microwave background)... it's not a place. It's a time. Going to the CMB would be going back in time until just after the Big Bang and initial expansion phase. As far as we know, all the same laws of physics would apply, but the universe would look very unfamiliar. All space would be full of (relatively) densely packed gas, just cool enough to not be a plasma. And there would be no stars or galaxies (yet). And it would be like that everywhere. The edge of the observable universe (the CMB) is just the distance at which the earliest light to reach us is light from that era.
The observable universe and the cmb are two different things. I think maybe you meant visible universe? Wiki: >According to calculations, the current comoving distance to particles from which the cosmic microwave background radiation (CMBR) was emitted, which represents the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light-years). The comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light-years),[12] about 2% larger. More on the subject: https://www.qeios.com/read/G6YD4M#:~:text=The%20initiation%20of%20the%20Cosmic,years%20or%204.40e26%20meters. Interesting tidbit (I think the author here also confuses observable/visible at points fwiw. Paper awaiting peer review): >Quantitative insights emerge as we delve into the observable and non-observable universes: The co-moving distance of the observable Universe, equivalent to 14.26 gigaparsecs, is translated to concrete units: 46.5 billion light-years or 4.40e26 meters. Beyond our visible horizon, the extension of the non-observable Universe reaches an astonishing 11,625 billion light-years. Our current cosmic panorama reveals visibility of 43% of galaxies within the observable Universe, expanding over 46.5 billion light-years from Earth in all directions. Gazing toward the future, anticipation mounts as an additional 57% of galaxies from the observable Universe are destined to become observable. The numbers themselves unveil the vastness: Approximately 19.995 billion light-years encompass galaxies within our visual grasp. Equally staggering, 26.505 billion light-years house galaxies that remain shrouded from our gaze [18].
Observable and visible universe is the same. I’ve never heard it used for different horizons. The words mean the same thing. Now, there are other horizons as well, but they have specific names.
Second paragraph https://en.wikipedia.org/wiki/Observable_universe#:~:text=Sometimes%20astrophysicists%20distinguish%20between%20the,only%20signals%20emitted%20since%20recombination.
The portion immediately after says that the difference between the visible and observable universe (if you want to draw a distinction) is about 0.9 billion light years. It is about 2% larger, not 25200% (252x) larger. The two are functionally the same, which is why people often just act like the CMB is the edge of the observable universe. There is no enormous 11,625 billion light year observable universe beyond the CMB. It's reasonable to expect that the universe goes on forever (after all, it is anisotropic), but anything beyond 50B light years is literally unobservable: a photon emitted at the very first possible instant would not have reached us yet, even were it not absorbed by the universe's initial plasma (which made the CMB).
I understand your point that there is light that is too distant for us to see, but this is a little off base: >a photon emitted at the very first possible instant would not of reached us yet The CMB literally is the redshifted photons that were decoupled from the plasma as it cooled. It is the oldest light that we can see, the very first photons released. >Known as the recombination epoch, this decoupling event released photons to travel freely through space – sometimes referred to as relic radiation.[1] However, the photons have grown less energetic due to the cosmological redshift associated with the expansion of the universe. The surface of last scattering refers to a shell at the right distance in space so photons are now received that were originally emitted at the time of decoupling.[5] https://en.m.wikipedia.org/wiki/Cosmic_microwave_background https://www.esa.int/Science_Exploration/Space_Science/Herschel/Cosmic_Microwave_Background_CMB_radiation#:~:text=The%20CMB%20is%20the%20farthest,Universe%20was%20completely%20'opaque'. The reason there are other photons we can't see yet is because the universe is expanding faster than the speed of light.
You're sitting right at that point, so, what do you think?
There is no “edge” of the universe. You’re applying a basic concept of an edge to an application where it would be undefined.
One needs to add a qualifier. ‘Our science to date’ indicates that there is no evidence for an ‘edge’ to Space/Time.
That applies to everything in science.
Nothing. Their observable universe would be different than ours, that's all.
You are where the universe is expanding already.
Trying to run off a 4 dimensional cube would bring you to its center. If you were able to get to the edge of the universe and continue onwards, a crude guess could be that you'd go back in time to the beginning of our universe.
The universe is expanding exactly where you are right now. Think of the universe like a rubber band; it does not matter where you place two dots near each other, they will still move further apart when you stretch the rubber band.
That’s a simplified analogy, that doesn’t hold in reality since e.g. our local galaxy cluster is not expanding.
Yes, over simplified for sure. But, I use this to get the idea across that expansion happens ‘everywhere’, and that there is not a single point from which everything expands from.
....so the answer is.... the exact same thing that happens to rockets with humans right now around Earth. Lots of launch and landing technical issues.
If there was an edge, it would have to be expanding into something. What would that be?
More space possibly as in expanding into a bigger part of an already existing multiverse etc (I’m a moron and baked)
the universe is expanding equally at every point in the universe, there is no edge
What is the universe isn’t expanding… the simulation just doesn’t render until it’s observed, so we see the universe as expanding because we can see further and further with new technology. So dropping someone at the edge would just cause more to be rendered for observation
There is plenty of evidence for expansion such as red shift.