AnnonBayBridge t1_j1gjb6q wrote
Reply to comment by Shadowkiller00 in Did you know it will still take 46 billion years to cross the universe at the speed of light? 65 mph = 4.8 * 10^17 years! by NotAndroid545
Question from non-expert: how is it possible the universe expanded to 40+ billion light years when it’s not even that old? Like did the universe expand faster than the speed of light?
Efficient-Finding-34 t1_j1gk236 wrote
Yes, the universe is expanding faster than the speed of light. This means that there are parts of the universe which we will never see.
TLRsBurnerAccount t1_j1gnrmz wrote
It'll be impossible to see, but I really wonder what the expanding edge of the universe actually looks like
duckiegooseman t1_j1goass wrote
Looks exactly like what you see from earth because it doesn't have an expanding edge, but rather the space between "things" just get bigger, so to an observer sufficiently far away, earth is on the edge of their observable universe
Artikay t1_j1gszt9 wrote
So if you place Earth in the center of our observable universe, and call it Planet A, then you take two planets on the far opposite ends and call them B and C. Does that mean to Planet A, B and C can be seen, but to planets B and C only Planet A can be seen?
Basically B and C have more than one observable universe between them? It would take exponentially longer for light to reach between stars because there is more space to expand between them?
If there is so much space between ends of the universe could two points be so far apart that light could never get from one end to the other?
Wind_14 t1_j1gu400 wrote
the last one is the consequences of observable universe though. Yeah there's a point where light simply can't reach the other side, because the expansion is faster than the speed of light, thus limiting the size of the observable universe (of course, this is assuming our prediction/projection is really true which is the farther an object is from the center the faster the expansion rate is between them and center).
And you don't have to assume that earth is the center of our observable universe, since it is (or rather the center of your observable universe is you).
duckiegooseman t1_j1hf4ic wrote
Yes to the last question. Actually since the universe is accelerating faster than light, every second more and more "things" get so far away they are "lost" to us permanently because light from them can never reach us anymore. At some point far far into the future, our cosmic horizon would be complete emptiness in every direction, and our galaxy would be the only thing that even exists to us anymore.
But to B and C, they don't exist for each other. Information from B can never reach C and vice versa.
TLRsBurnerAccount t1_j1gp27x wrote
I guess what I mean more I wonder what it's like being beyond the edge of the universe and essentially being crested by the edge
420binchicken t1_j1gpqoh wrote
AFAIK that’s not really how it works. For them, they are the centre point at which the universe is expanding from. It’s all relative to your own frame of reference. No solar system is more on the ‘edge’ of the universe than any other.
Please someone correct me if that’s wrong. Space is big and weird.
inventionnerd t1_j1gs85e wrote
This is true if we're going off the belief the universe is infinite. Then yes, everyone can only see in a 46b radius and are therefore at the "center" of their universe.
sbrt t1_j1gtcr9 wrote
It was explained to me that it is the 3d equivalent of a 2d creature living on a globe that is expanding. I can imagine that but I have no idea if it is accurate.
ZincMan t1_j1i1jce wrote
Can we judge our location in relation to the “true” center of the universe ? I mean I assume if the Big Bang was centralized, there must be a “core” to that expansion where everything is expanding radially outward…. But now that I think about it, it still might appear as though everything in relation to you is leaving your observable edge of the universe at equal speed regardless.
inventionnerd t1_j1i2ctp wrote
It wasnt centralized though. Basically the current theory is the universe is/was always infinite and is just a bigger infinite now. The mass might have been far denser and closer together before the space expansion, but it wasnt in like a 1 mm radius sphere or something. It was always in an infinitely sized space.
gtga1976 t1_j1i4b96 wrote
That's space itself though yes? I assume the mass within space shows differential in red shift relative to earth based on some other central point? Or are you saying everything is travelling away from earth at the same speed?
inventionnerd t1_j1i8w3u wrote
Not quite sure what you're saying, but no, everything isn't traveling from Earth at the same speed. But I'm saying wherever you are in space, you'd see the same frequency if you look far enough as you see on Earth? So, our observable universe is about 46b lightyears in radius. To us, we're at the center right? We see a redshift of x when looking straight "up" to the very edge of our universe. If we can teleport to this this spot instantly and look around us, we'd still see a universe of about 46b lightyears in radius (just would be mostly different things as you could see from Earth. If you then looked straight "up" from this spot, you'd still see the same redshift of x as you saw when you looked at your current spot from Earth. So, how could you ever tell what the central point is if everywhere you go, you'd have the same size observable universe and same shifts?
The_Most_Superb t1_j1gu3pk wrote
There is only existence and non existence. Beyond the universe is nothing. Unfathomable nothingness.
Caveman108 t1_j1gwkoj wrote
Except we don’t know that. If you could travel multiple times the speed of light, ideally many multiples, you could reach the edge of the observable universe. There you very well might just find more universe. We don’t know there’s an “edge.” Just an edge of what we can see.
Smartguyonline t1_j1h3opp wrote
It looks exactly like it does from right here 🤯
museabear t1_j1gpsvz wrote
And what’s on the other side.
TransportationIll548 t1_j1gt7f7 wrote
nothing is on the other side
[deleted] t1_j1gx3c8 wrote
[removed]
Smartguyonline t1_j1h3xg2 wrote
There is no “other side” of the universe or “before” the Big Bang. Those concepts don’t make any sense.
DWright_5 t1_j1guykl wrote
Why isn’t the speed of light the speed limit?
woodlark14 t1_j1hfcgi wrote
The speed of light is how fast an object can move through space, but the universe isn't expanding by motion, it's expanding by changing the size of space. To us an analogy, consider a balloon with objects on its surface. The speed of light is how fast objects can travel across the surface of the balloon, but if the balloon is inflated then the distance between two objects can change faster than that speed.
ZincMan t1_j1i27ci wrote
I understand what you’re saying but I don’t get how the expansion speed and “travel” speed would have different hypothetical limits. If things are expanding, I’m assuming it’s “relative speed” but it is indeed traveling faster than the speed of light relative to something … or rather why does traveling through space have a speed limit at all?
woodlark14 t1_j1i3ljj wrote
From the perspective of relativity, everything is always moving at a constant speed through space-time from every perspective. The faster something is moving through space, the slower it is moving through time and vice versa. Light speed is achieved when an object has no mass, resulting in it travelling entirely through space and experiencing no time passing. There's a whole bunch of effects that result from this like length contraction and time dilation.
Space expansion is very different, It has nothing to do with the object you are observing, it is instead a property of the space between you and the object. In a sense neither object has relative motion, instead the ruler you are using to measure the distance between the two is changing it's length.
ZincMan t1_j1i6t4n wrote
Fucking hell. I don’t even understand your first sentence. However what your 2nd paragraph is saying I think I get. Does expansion not count as moving through space ? I understand expansion speed is relative to the observer, but surely the fastest things could expand away from each other has to be twice the speed of light right ? Like if two objects are “expanding” away from each other at the speed of light in opposite directions… their relative speed to each other would seem as though they are traveling twice the speed of light right ? (Assuming you could observe) I guess my questions is can expansion travel faster than this ? Faster than two objects speeding away from each other at light speed ? I don’t get the difference between travel vs expansion. Is expansion actually Stretching reality itself?
woodlark14 t1_j1iczf1 wrote
Apologies, relativity is quite hard to explain especially without diagrams. The answer to your other questions is that it is reality that is stretching, the distance between two galaxies becomes larger rather than one of the two galaxies moving into a new space. So it's not limited by the speed of light.
As for your questions about the fastest two things can move away from each other, that's actually a more complicated question than you realise. The issue here is that the maximum speed anything can be observed to be moving at is the speed of light. If you took two objects moving away from you at 0.75c (0.75 times the speed of light) then from the perspective of one of those objects the other wouldn't be moving at 1.5c. Instead it would be moving at 0.96c, and you would notice that clocks on the objects no longer match yours.
JasonMontell2501 t1_j1gxmnj wrote
It actually is the speed limit for everything except the universe itself
TheMarketLiberal93 t1_j1h2ks1 wrote
Expanding into what?
Smartguyonline t1_j1h41c1 wrote
What do you mean? Space itself is expanding everywhere.
TripleATeam t1_j1gki0d wrote
Not only what everyone else says, but space seems to expand at a constant value per unit of volume. Thus the more space there is, the faster it expands. Thus eventually (as far as we know rn) we'll stop seeing other galaxies. We'll be alone.
f_d t1_j1gva4w wrote
The Local Group is bound together by gravity. It should stay together as long as the fundamental forces keep working like before. The rest of the universe outside that threshold will keep stretching away endlessly.
TripleATeam t1_j1gvm96 wrote
I thought it was just the galaxy that was bound tightly enough and the local group would eventually go as well? Huh. I guess I learned something.
mavric91 t1_j1gm8kr wrote
A metaphor I’ve always liked is the raisin bread one. In this metaphor, the raisins are galaxies, and the dough/bread is space-time. When you bake the loaf, the dough rises and expands. And once the loaf has finished baking the raisins are now farther apart than when they started. But they aren’t farther apart because they moved through the dough away from each other. They are farther apart because the dough expanded. The substrate they exist in expanded, space between them expanded, and now they are farther apart.
So when we talk about the universe expanding, we aren’t talking about galaxies simply drifting farther away from each other. We are literally talking about space itself expanding. The emptiness itself between galaxies gets bigger. And that process can happen faster than the speed of light.
It’s also worth noting (and I’m not that up to date on this so someone correct me) that the Big Bang isn’t like everything just started expanding from a single point at the speed of light. It’s more like all of a sudden everything just was. Not instantaneously, but in a matter of seconds the early universe just was, and it was big (millions? Billions? of light years big). And from that point it began to rapidly span outwards. And again, the Big Bang wasn’t all of a sudden matter exploded into the empty space-time of our universe. The Big Bang created our universe. It created space. Before it there was nothing. Not nothing like empty intergalactic space nothing. I mean like no-such-thing-as-empty-space nothing.
So yah the universe can expand that much in a short amount of time.
highjinx411 t1_j1gp9bm wrote
Weird. It just makes me crazy thinking about there being nothing and then something for no reason at all.
mavric91 t1_j1gpxnc wrote
Yah the trick that works for me is just to not think about it too hard or else I risk full existential crisis.
starsblink t1_j1h03e5 wrote
I just like to think that we don't know yet. Our universe could be inside a grain of sand on a beach we can't see yet.
f_d t1_j1gwp98 wrote
>It’s also worth noting (and I’m not that up to date on this so someone correct me) that the Big Bang isn’t like everything just started expanding from a single point at the speed of light. It’s more like all of a sudden everything just was. Not instantaneously, but in a matter of seconds the early universe just was, and it was big (millions? Billions? of light years big). And from that point it began to rapidly span outwards.
The idea is that all the energy and space started out packed together densely, then rapidly expanded everywhere at once similar to how space is expanding everywhere at once today. Even when it was packed together densely, it could have been infinitely large. Just denser than it is now.
Ebonicus t1_j1gx706 wrote
I wonder if the space between all quarks is also expanding. Meaning the raisins are getting bigger and we won't notice it, because the ruler is getting bigger too.
e36freak92 t1_j1gk0sj wrote
Yes, there are galaxies moving away from us at faster than the speed of light. The expansion of spacetime itself isn't constrained by special relativity.
Also it's expanding everywhere at once, not just the borders getting father away, which is really hard to wrap your head around
Aldodzb t1_j1gnjqk wrote
So the black background we "see" it's just more universe but we cannot see it because we are getting apart from each other at a speed faster than the light?
Can something move away from us, in a direction, faster than the speed of light and something else in the same direction but opposite way too? It seems odds, where are moving then?
norbertus t1_j1glbyo wrote
> Yes, there are galaxies moving away from us at faster than the speed of light
No, "the speed of light" is a cosmic speed limit. There is no valid mathematical framework for "galaxies moving away from us at faster than the speed of light"
As an inertial body approaches "the speed of light" (which varies by medium, causing, for example, the optical effect of "index of refraction"), the amount of energy required to continue to accelerate that body approaches infinity.
bendvis t1_j1glyal wrote
Right, but all of those rules only apply to objects moving through space. Space itself is also expanding, and taken with the movement of the galaxies through space, distant galaxies are moving away faster than light.
That is, if you fired a laser at one of those galaxies today (and assuming the universe continues to expand forever) the light from the laser would never get there. The distance between the ray of light and the galaxy would continue to grow even though the galaxy isn’t moving through space faster than light.
polovstiandances t1_j1gmpfo wrote
How is it possible? What does galaxies “moving away” actually mean? Isn’t the space expanding at the edges like a droplet of water or something?
bendvis t1_j1gnl3b wrote
The common analogy is an ant crawling across the surface of an inflating balloon toward a specific spot. The spot is stationary on the balloon’s surface and the ant is moving toward the spot, but the distance between them is growing because the size of the balloon is growing.
Compare the expanding 2d surface of the balloon to space itself, and that’s why distant galaxies are moving away. Like the spot, they’re maybe not moving, but the distance between us and them is still growing.
polovstiandances t1_j1gofji wrote
Thanks for your reply. So then how can one explain why the rate at which this expansion process happens isn’t a function of the speed of light at all? If the analogy serves, I can only blow a balloon up as equivalently fast as the speed of light, meaning there’s some max distance that can be produced in some time delta between the ant and the target spot, no?
420binchicken t1_j1gq6pn wrote
No, the speed at which the balloon can inflate, or the universe can expand, is not limited by the speed of light. The speed of light is a speed limit for things moving across that space, not the space itself expanding.
polovstiandances t1_j1gqrop wrote
Ok, well that’s like, fucking insane right? Maybe my understanding of the concept of space needs revision because conceptually I believe space to still be an object, and nothingness to be space, meaning that an “object” is still moving across a plane (of nothingness) at a rate. But this isn’t very physical or scientific I guess
bendvis t1_j1grw9y wrote
Imagine a wave traveling through water. Each water molecule doesn’t really go anywhere. It just gets bumped and jostled by its neighbors and it ends up moving in a circle as the wave passes through.
Light is a wave too. It’s a wave passing through the electromagnetic and mass fields in the same way that a wave passes through water. Light is a vibration that propagates through those fields. So, empty space is an area whose fields aren’t vibrating. The fields are still there just like water is still there when there isn’t a wave passing through it.
polovstiandances t1_j1gs4lm wrote
Oh wow, this was a really helpful image. Thank you. Damn I should have studied this shit.
bendvis t1_j1gpibe wrote
The speed at which you can stretch a balloon’s surface and the speed at which an ant walks across the balloon’s surface are distinct and separate things that aren’t related.
The same is true of the speed at which light (or gravitational waves or information in general) propagates through space and the space it’s propagating through. They’re not related.
Keep in mind that space expanding happens ‘faster’ on bigger scales. If 10 cm of balloon distance expands to 11 cm over the course of a minute, then the points that were 10 cm apart are moving away from each other at 1 cm/minute, even though neither point is moving across the balloon in its own frame of reference. If the balloon were enormous with two points 10 light years apart and it expands at the same rate, they’d be moving apart at 1 light year per minute - much faster than the speed of light.
polovstiandances t1_j1gpzu1 wrote
Ok this makes sense. But still doesn’t touch on how fast spade can expand, and whether there is a max limit to that. But I guess you’re saying that yeah, space still cannot expand faster than a certain rate, it’s just that the rate it expands informs a different understanding on the time plane. But space cannot expand faster than the speed of light, right? What I mean is just the raw rate at which the universe is expanding must be some function of an expansion rate even if it causes the amount of total space to exceed the distance achievable by the speed of light, right?
bendvis t1_j1gqo13 wrote
According to one theory, during a time called Inflation, space expanded really fast. The volume of space expanded 10^78 times larger in 10^-32 seconds. That was way faster than the speed of light. This super rapid expansion explains why the cosmic background radiation is so nearly perfectly even - because at that time in the early universe, it was all in one point. If there is a limit, it would have to be faster than that.
polovstiandances t1_j1gqx97 wrote
That’s fucking nuts. I need to know more. Thanks.
bendvis t1_j1gs98d wrote
My wife and I just discovered a really well done YouTube channel called Astrum. Their video on black holes is fascinating and covers this stuff in a clear and straightforward way. Highly recommended!
f_d t1_j1gysd5 wrote
>This super rapid expansion explains why the cosmic background radiation is so nearly perfectly even - because at that time in the early universe, it was all in one point.
It wasn't necessarily in one point, it was just extremely dense and homogeneous. Space could have been infinite even when everything was packed together tightly.
East-Dot1065 t1_j1gofq8 wrote
Another analogy I've seen used you can do yourself.
Place your hands flat on a table with your fingers together and the tips of your thumbs touching. Keep your thumbs touching and move your hands apart while spreading your fingers slowly. No one finger tip will be moving faster than the next, but the tips of your pinky fingers will be moving away from each other much faster than anything else. That's because distance between them is growing no matter their movement.
polovstiandances t1_j1gojw0 wrote
Thanks for the reply. Check my other comment too, I’m very curious.
norbertus t1_j1gmtwa wrote
The speed of light represents a limit for how fast local interactions can be propagated in space-time, or, how quickly an inertial body can traverse a reference frame.
Einstein's relativity is still within the classical Newtonian framework governed by locality, causality, and determinism, but Einstein's major insight was that Newtonian "absolute space" does not exist.
https://plato.stanford.edu/entries/newton-stm/
In relativity, it does not matter if space is expanding when we are trying to reason about things like how fast a distance can be traversed. In relativity, speeds are not additive and subtractive the way speed works in the grade school math problem about two boats on a river.
https://www.onlinemath4all.com/boats-and-streams.html
Einstein formulated general relativity in the wake of a major failed experiment, probably the most important failed experiment of the last 150 years.
The Michelson-Morley experiment was trying to measure the speed of light relative to the rotation of the earth by measuring its differential at a given point on the earth rotating either into or away from light streaming out from the sun
https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment
It turns out there is no difference in the measurable speed of light, which paved the way for relativity.
As it turns out, relativity is what makes GPS work
https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html
And 1905 was the magic year Einstein invented relativity and quantum mechanics (by defining "the quanta")
https://en.wikipedia.org/wiki/Annus_mirabilis_papers
edit: typo
bendvis t1_j1go9t0 wrote
I mean… I appreciate the long-winded explanation of how light moves through space, but none of it covers how space itself expands and how that can make distant objects move away from us at faster than light.
Again, the galaxies are not moving through space faster than light, but the distance between us and them is growing faster than light-speed because of the expansion of space.
They are effectively moving away faster than light. If you magically took off toward one today at light speed, you’d never reach it.
norbertus t1_j1gojn0 wrote
>long-winded explanation
A joke on the "Aether wind?"
> but the distance between us and them is growing
Missed that, you're quite right there, space itself is expanding.
belugwhal t1_j1gpwkb wrote
>As it turns out, relativity is what makes GPS work
Err...I think you mean relativity must be taken into account for GPS to work. If relativity wasn't a thing, GPS would still work (it would just be easier).
norbertus t1_j1gr1b7 wrote
>relativity must be taken into account for GPS to work. If relativity wasn't a thing, GPS would still work
That statement is logically inconsistent.
The paper I cited above
https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html
describes the role of relativistic "time dilation" in the functioning of the GPS coordinate system
https://en.wikipedia.org/wiki/Time_dilation
relative speed and the relative strength of a gravitational field each affect the local measurement of "time."
In the case of a GPS satellite, which is out in space and farther from us (its users -- and the earth as a gravitational well) and moving faster relative to us (because they need to stay in orbit and constantly fall over the horizon while we are stationary on the ground), these relativistic effects work at cross-purposes.
GPS uses not triangulation to determine a location, but tri-lateration with a fourth satellite to account for timing delays due to relativity.
The paper I cited notes " If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day"
belugwhal t1_j1gtk7j wrote
Umm.. what I said agrees with this. Dude... You wrote all that for nothing. Maybe reread my comment.
RedMistStingray t1_j1gr3vv wrote
This is easy to conceptualize. If the universe started from a singularity and expanded in all directions, at the speed of light 13 billion years in one direction and 13 billion years in the other direction, that is at least 26 billion light years across. But space is expanding faster than the speed of light, not to mention ALL space is expanding everywhere. It's easy to see why the observable universe is 40+ billion light years across.
A better question would be, do we have any idea how large the entire universe is, including what we can't see? We must be able to calculate how much of the universe we can't see.
Baskin5000 t1_j1gjvra wrote
It’s not this simple, but:
Imagine you stretch your arms out to the side and each arm grows one foot every 1 year. After one year you’ve grown 2 feet of arm length. The universe is like that but more complicated
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