Submitted by _bidooflr_ t3_11isl13 in askscience
Narwhal_Assassin t1_jb3mcuo wrote
Reply to comment by DevinVee_ in Does the age of the universe depends on where you are? by _bidooflr_
Imagine taking a picture of yourself and mailing it to your grandma. That picture shows how you look on the day you take it. It then travels through the postal system for a couple days (or weeks, or months, depending on how bad the system is). In that time, you could change a lot: you could shave your eyebrows, or dye your hair, or get a tattoo, or go tanning. However, the photo still shows the you from a couple days ago, so when your grandma sees it she only knows what you looked like then. The further away she lives, the more stuff can change in the meantime.
In the same way, photons are like pictures of the stuff that emitted them. When the Big Bang happened, a bunch of photons got shot out in all different directions. At the same time, space itself expanded, and it expanded a lot. The distance those photons had to travel went from almost zero to millions of light years faster than they could traverse it. Imagine if the postman was walking the 20 feet to your grandmas mailbox, when suddenly it grew into a 30 mile hike. He’d take a lot longer to bring her the mail. Eventually though, he would make it, and grandma would finally see your lovely face. In the same way, these photons would eventually make it to us, and we could see the early universe: it just takes 13 billion years to cross that gap, since space just keeps expanding while the photons move.
So yes, those photons are from the early early universe, because space itself expanded and made them travel for longer to reach us.
DevinVee_ t1_jb4hg63 wrote
No I understand how the speed of light works. What I don't understand is how earth, sun, solar system, physical matter. Beat photons "from the beginning of the universe" so if it took this light 13 billion years to reach us , it must've taken far longer for us to get to this exact location we are at when we saw it. Meaning a far greater amount of light has already gotten to this point and past. Nothing travels faster than light. So how is it we as physical objects are seeing the fastest thing in the universe just now get here? It's like if grandma left at the same time as the mailman and somehow getting to her house first.
The only other explanation is that all the matter of the universe did not come from the big bang and "we" we're already here.
Please note I use we not as humans but as a place holder for our solar system or our location.
Narwhal_Assassin t1_jb58rm4 wrote
Ok I see what you mean now. Ordinarily, you would be exactly right: there’s no way we could’ve gotten that far away from the photons that they would take 13 billion years to reach us. However, early universe is anything but ordinary.
Going back to grandma and the mailman, imagine they’re both on the sidewalk, but grandma is on the side closer to the house. At the same time, they both start to move towards the house, but as grandma steps off the sidewalk, it suddenly quadruples in size. Grandma is fine since she already got off the sidewalk, but the mailman suddenly has to walk four times as far to catch up. Then, as he hits the halfway point, it quadruples again. And as he keeps going, it keeps getting bigger and bigger. Grandma already made it to the porch and is knitting a sweater, but the mailman hasn’t even gotten off this piece of sidewalk.
This is how the early universe looked. In the first instants after the Big Bang, some photons were going the same direction but from different places. Because space expanded so rapidly, the photons with a “head start” in their direction got a lot further ahead than the others, and this head start kept growing as space continued to expand. Except instead of doubling or quadrupling, it was expanding by millions and billions. Even though they started so close in the beginning, a gap of a nanometer could expand to a light year faster than the photons could cross it, so they got left in the dust.
Remember that all the stuff we see and interact with started off as photons too, just running a shorter race, so after they got here and started settling down into planets, the other photons were still trying to overcome the vast distance that space itself had made by expanding
DevinVee_ t1_jb5c59e wrote
but isn't "space expanding" just matter/objects spreading apart from each other? space isn't a physical thing it's the absence of physical things. So, space expanding in this spot faster than this spot just means these two objects are moving away from each other faster than these other two things are moving away from each other. This still doesn't solve the issue that if the Earth is x distance away from the hypothetical center of the universe (something afaik we haven't determined its location) where we are seeing this light come from, that light theoretically can't be from the big bang, other wise it would imply that the Earth was in this location before the big bang occurred, or that light would've passed through here already.
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If you're saying space expands faster than light in certain spots in the universe fine that happens, but saying that means the distance between Earth and the hypothetical center of the universe has expanded faster than the speed of light meaning Earth has traveled faster than the speed of light. Which is impossible according to our understanding of physics.
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So with that, I see it as a few possible explanations..
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The light we are seeing today from 13 billions years ago (i.e. 13 billion light years away) was, in fact, not the first lights after the big bang.
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The lights we are seeing are just "the earliest lights after the big bang" that we've seen and "The first lights after the big bang" is simply click-bait titles. This means that we will never see any light source from the initial big bang or shortly there after because that light has already passed us by. (hypothetically we could see the refraction from a large gravitational force bending said light back but for it to bend back in exactly the same way to reflect something understandable seems impossible.)
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The lights we are seeing are from the opposite side of the universe from a source that is expanding just as rapidly (but not at the speed of light) from us and we can actually see the center of the universe -- We know we've seen things that are moving away from us, but have we seen anything moving the exact opposite direction from us? Specifically multiple things?
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the big bang is a lie, everything is just floating around nothing is moving away from a specific point.
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These are the things that confuse me every time some one mentions the "First lights of the universe" how can that possibly be? regardless of the expansion of space moving faster than the speed of light.
Narwhal_Assassin t1_jb66t7l 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).
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.)
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