Submitted by _bidooflr_ t3_11isl13 in askscience
Narwhal_Assassin t1_jb66t7l wrote
Reply to comment by DevinVee_ in Does the age of the universe depends on where you are? by _bidooflr_
Space is a real thing that can expand. If you’ve heard phrases like “the fabric of spacetime” or “the spacetime continuum”, these are actually real, not just some sci-fi mumbo jumbo. You can imagine a big rubber sheet, on which all the planets and stars and everything are sitting. If you label this sheet with a grid and stretch it out, you’ll see that stuff gets further apart, but it doesn’t change position on the grid. That’s how space expands: it doesn’t move things, it just makes the distance between them bigger. (Note: don’t take this analogy too far: unlike rubber, space can stretch infinitely, and it doesn’t “snap back” into place).
So space expanding makes distances bigger, but it doesn’t make objects move any faster. Nothing ever moves faster than light, even when space expands. It just travels a shorter distance, so it can get places earlier.
Also, there is no “center” of the universe. No matter where you are, whether on Earth or on Jupiter or floating somewhere in the middle of the Andromeda Galaxy, if you take the measurements and do the calculations, you’ll find that you are at the center. Every single point in the universe can be treated as the “center”, and every single one of those points would be perfectly accurate for any tests or measurements or calculations you could think of. So, either everything is the center, or nothing is, but there’s not one singular point we can look at and say “yeah that’s the literal exact center and nothing else is.”
DevinVee_ t1_jb6tvq0 wrote
But if the grids don't get bigger they are the same distance, always. Otherwise the two objects are, in fact, moving. If there is no center of the universe then where'd the big bang happen?
Btw I'm really not trying to sound like I'm arguing. I'm actually enjoying this conversation most people I talk to just go "oh, huh, yea that's crazy....so did you want to order something?"
_mizzar t1_jb8si63 wrote
Your primary misunderstanding is that the past we are seeing into is not the past of “our part” of the universe.
The universe is likely infinite. The observable universe is a sphere with us in the middle. The edge of the sphere is where we see the oldest parts of the universe because the light from these distant places is just now reaching us, showing us what things looked like back then.
This sphere is getting bigger for an obvious reason, more and more light from distant places is reaching us. However, the sphere is also getting bigger because the entire universe (not just the observable universe sphere) is expanding.
Careful here not to imagine the entire universe’s expansion as a sphere, but rather every galaxy that isn’t locally bound to another galaxy by gravity is moving away from one another.
An oversimplified way to imagine this is to visualize an infinite 3D space with tennis balls each 10 meters from one another in every direction. Move forward through time and as the universe expands they are now 20 meters away from one another. Move back in time and they are 5 meters away from one another and so on.
The interesting thing is that, though the speed of light is constant, this expansion of the entire universe seems to happen faster with the more space that there is between things, as if the space itself was causing the expansion (we call this expansion Dark Energy).
What this means is that eventually the expansion of the entire universe will greatly outpace the speed of light, making galaxies we can currently see in the observable universe fade out of sight as they slip out of our observable universe. Eventually, only our own galaxy (at this point merged with Andromeda) and perhaps a few others in our local group will visible to us, everything else too far away and the universe expanding too fast for new light to reach us.
If humans still exist in this time, they would have no knowledge of other galaxies and the universe unless we managed to pass down the data from our time.
Aseyhe t1_jb7e5vt wrote
> Space is a real thing that can expand. If you’ve heard phrases like “the fabric of spacetime” or “the spacetime continuum”, these are actually real, not just some sci-fi mumbo jumbo. You can imagine a big rubber sheet, on which all the planets and stars and everything are sitting. If you label this sheet with a grid and stretch it out, you’ll see that stuff gets further apart, but it doesn’t change position on the grid. That’s how space expands: it doesn’t move things, it just makes the distance between them bigger. (Note: don’t take this analogy too far: unlike rubber, space can stretch infinitely, and it doesn’t “snap back” into place).
This is kind of a problematic way of thinking, because there isn't any objective sense in which space or spacetime can move or stretch. Those kinds of effects only ever represent subjective choices, often made to simplify a mathematical problem. They are coordinate choices, specifically. The only objective property of a point in spacetime is its (tensor) curvature.
For example, the idea of space expanding is a coordinate choice. It's equally valid to just say that objects are moving apart.
(How, then, can things recede "faster than light"? Just as it's not possible to uniquely define the angle between arrows drawn at different places on a curved sheet, relative velocities of distant objects in curved spacetimes are not meaningful.)
Viewing a single comment thread. View all comments