# Thread: Speed of Light/Expansion of Space

1. I'm having a hard time wrapping my head around this problem. Light travels from point A to point B within the universe (say galaxies). Since space is expanding, and light travels relative to space (I'm assuming) than the time it takes for light to get from point A to B is effected by that expansion. So does it take less time or more time? Would it take less time, more time or the same amount of time as 2.54 million years for light from Andromeda to reach us?

2.

3. Originally Posted by Golkarian
I'm having a hard time wrapping my head around this problem. Light travels from point A to point B within the universe (say galaxies). Since space is expanding, and light travels relative to space (I'm assuming) than the time it takes for light to get from point A to B is effected by that expansion. So does it take less time or more time? Would it take less time, more time or the same amount of time as 2.54 million years for light from Andromeda to reach us?
Generally the expansion of the universe causes light to take longer than it otherwise would to go between distant points -- like running agsinst a conveyor belt causes you to take linger to get to the end.

But in the particular case of the Andromeda galaxy, part of our gravitationally bound local group, the effects of expansion are negligible.

4. as you ofen tell me , dr rocket send your anser to psadosciense , thanks in advens

5. Originally Posted by Water Nosfim
as you ofen tell me , dr rocket send your anser to psadosciense , thanks in advens
More proof that you know nothing and Pseudoscience is the right place for you.

My answer is correct. It is standard cosmology, deducible from the general theory of relativity. In fact there are galaxies,outside of the "Hubble sphere", that, due to the accelerating expansion of space, will NEVER be seen by us. Others, seen now, will eventually disappear.

Some people remain silent and are suspected of being fools. You choose to speak out and thereby eliminate all doubt.

6. Originally Posted by DrRocket
Originally Posted by Water Nosfim
as you ofen tell me , dr rocket send your anser to psadosciense , thanks in advens
More proof that you know nothing and Pseudoscience is the right place for you.

My answer is correct. It is standard cosmology, deducible from the general theory of relativity. In fact there are galaxies,outside of the "Hubble sphere", that, due to the accelerating expansion of space, will NEVER be seen by us. Others, seen now, will eventually disappear.

Some people remain silent and are suspected of being fools. You choose to speak out and thereby eliminate all doubt.
dude that is so friggin epic

imagine of all of the galaxies in the universe like the milky way containing earthlike planets in them, and the possibility of evolution occurring on each of them... like the drake equation applied to the rest of the universe. wow. that's like having alot of interesting species and races of life we'll never meet or discover someday...

i wonder if each galaxy have their own unique elements present in them that aren't found in the milky way... so much undiscovered potential... that's like another distant galaxy never getting to meet or see anything of the milkyway galaxy...

I wonder if time-space is different per galaxy... like our galaxy is near the center of the universe, where as other galaxies are spread out further... i wonder if universal laws/physics and properties are different for galaxies like those... would being further away from intergalactic communities (intergalactic gravity/light/em spectrum emissions), affect how another galaxy exist (being further out away from those things)?

7. Originally Posted by FuturePasTimeCE
dude that is so friggin epic

imagine of all of the galaxies in the universe like the milky way containing earthlike planets in them, and the possibility of evolution occurring on each of them... like the drake equation applied to the rest of the universe. wow. that's like having alot of interesting species and races of life we'll never meet or discover someday...
The issue is not evolution, but rather abiogenesis which is a completely different thing. We know essentially nothing about abiogenesis, but as molecular biology turns biology from cataloging to real science we will probably come to understand the possibility much better.

The Drake equation has no real scientific content, so one cannot use it sensibly -- science fiction notwithstanding.

But, as a personal opinion only, I observe that life somehow arose here, and the universe is a big place. It is a REALLY big place. I would be very surprised if there were not life elsewhere. Maybe not in this galaxy or Andromeda or elsewhere in the local group, but even that vast expanse is only a tiny part of the universe.

Originally Posted by FuturePasTimeCE
i wonder if each galaxy have their own unique elements present in them that aren't found in the milky way... so much undiscovered potential... that's like another distant galaxy never getting to meet or see anything of the milkyway galaxy...
Almost certainly not. All evidence is that the laws of physics are the same throughout the universe. That fact is what allows us to understand the universe while remaining bound to Earth, or at least to our solar system.

Originally Posted by FuturePasTimeCE
I wonder if time-space is different per galaxy... like our galaxy is near the center of the universe, where as other galaxies are spread out further... i wonder if universal laws/physics and properties are different for galaxies like those... would being further away from intergalactic communities (intergalactic gravity/light/em spectrum emissions), affect how another galaxy exist (being further out away from those things)?
There is no center of the universe. That is a consequence of what we know from general relativity about the big bang. Another way to look at it is that EVERY point in the universe is the center -- no point is distinguished.

8. Originally Posted by DrRocket
Originally Posted by FuturePasTimeCE
dude that is so friggin epic

imagine of all of the galaxies in the universe like the milky way containing earthlike planets in them, and the possibility of evolution occurring on each of them... like the drake equation applied to the rest of the universe. wow. that's like having alot of interesting species and races of life we'll never meet or discover someday...
The issue is not evolution, but rather abiogenesis which is a completely different thing. We know essentially nothing about abiogenesis, but as molecular biology turns biology from cataloging to real science we will probably come to understand the possibility much better.

The Drake equation has no real scientific content, so one cannot use it sensibly -- science fiction notwithstanding.

But, as a personal opinion only, I observe that life somehow arose here, and the universe is a big place. It is a REALLY big place. I would be very surprised if there were not life elsewhere. Maybe not in this galaxy or Andromeda or elsewhere in the local group, but even that vast expanse is only a tiny part of the universe.
but the drake equation is based on our own earthly evolution within the milkyway... that's like saying it's impossible for any of us, including YOU (a organism composed of the elemental biochemistry of biology and elements of the universe, more notably considered evolution) to naturally exist because our existence is science fiction in your words.

Originally Posted by FuturePasTimeCE
i wonder if each galaxy have their own unique elements present in them that aren't found in the milky way... so much undiscovered potential... that's like another distant galaxy never getting to meet or see anything of the milkyway galaxy...
Almost certainly not. All evidence is that the laws of physics are the same throughout the universe. That fact is what allows us to understand the universe while remaining bound to Earth, or at least to our solar system.

Originally Posted by FuturePasTimeCE
I wonder if time-space is different per galaxy... like our galaxy is near the center of the universe, where as other galaxies are spread out further... i wonder if universal laws/physics and properties are different for galaxies like those... would being further away from intergalactic communities (intergalactic gravity/light/em spectrum emissions), affect how another galaxy exist (being further out away from those things)?
There is no center of the universe. That is a consequence of what we know from general relativity about the bog bang. Another way to look at it is that EVERY point in the universe is the center -- no point is distinguished.
where the big bang occurred, denotes the center of the universe. everything expanded from the big bang, from the region in which it occurred. Center of the Universe = Spot where Big Bang occurred where the majority of newer galaxies are formed.

9. where the big bang occurred, denotes the center of the universe. everything expanded from the big bang, from the region in which it occurred. Center of the Universe = Spot where Big Bang occurred where the majority of newer galaxies are formed.
Where is the centre or edge of the surface of an inflating ball? Same thing more or less. There is no centre. All that happens is that the surface area increases.

In our universe there is no centre or edge, but the total volume increases. On the surface of a ball like the earth, you can walk in one direction and will eventually end up back where you started. As the ball expands you will have to walk increasingly larger distances to get back to where you started. As our universe expands, you will have to go increasingly longer distances to end up back where you started. You will end up back where you started even if you went out in a perfectly straight line from your perspective.

10. The analogy of 2-D ants on the surface of an expanding balloon springs to mind. Which then makes me wonder if our own perception of the universe is a bit like that of the ants on their world. One ant philosopher might be very insistent that the universe has no edge, and thus takes no notice of his student who claims there is actually an edge in an extra dimension.

If the universe existed within some hyper-dimensional space would it have an edge then?

11. Originally Posted by FuturePasTimeCE
where the big bang occurred, denotes the center of the universe. everything expanded from the big bang, from the region in which it occurred. Center of the Universe = Spot where Big Bang occurred where the majority of newer galaxies are formed.
The big bang occurred EVERYWHERE. There is no center of the universe. It ws not an explosion in space. It was an explosion of space. That is the best that it can be described without using some fairly advanced mathematics.

12. Inappropriate post and responses removed.

13. wait i have a question, due to the past 40~50 years of experimental and theoretical physics, we know that space itself is expanding right? But if space is expanding doesn't that mean we are also expanding?

im alittle confused on this, i would appreciate if someone could explain though it might be real simple.

14. Take this with a grain of salt, but I think what's happening is that the gravitational forces (for the stars and planets) and the electromagnetic forces (in people and objects) are pulling things together more than expansion is pulling them apart. So we expand a little, but then collapse back to where we started (in a continuous process, so we don't see it happening). Since the expansion is accelerating, this won't always be true (see the Big Rip).

15. Originally Posted by Golkarian
I'm having a hard time wrapping my head around this problem. Light travels from point A to point B within the universe (say galaxies). Since space is expanding, and light travels relative to space (I'm assuming) than the time it takes for light to get from point A to B is effected by that expansion. So does it take less time or more time? Would it take less time, more time or the same amount of time as 2.54 million years for light from Andromeda to reach us?
It depends. Are you using the value of distance upon arrival, or the value of distance upon departure? If space is expanding, and Andromeda is 2.54 million light years away right now, then it must have been closer when the light was emitted that reaches us today. If so, then that light took less than 2.54 million years to reach us, because it traversed some of the distance prior to the expansion.

What going I'm to say isn't quite mathematically accurate, but it should serve as a sufficient description of what is happening:

Suppose the total distance had been 2 million light years flat when the light was emitted, and in the time it took it to get half way here, the total distance expanded to 2.26 million light years (it wouldn't be that number, because you have to account for the continuousness of it, but I'll use it for simplicity)

That means the light got half way here by traversing 1.13 million miles. In a static (non expanding) universe, it would have to traverse 1.26 million miles to get half way here.

16. Originally Posted by Heinsbergrelatz
wait i have a question, due to the past 40~50 years of experimental and theoretical physics, we know that space itself is expanding right? But if space is expanding doesn't that mean we are also expanding?
Yes as far as we can tell space is expanding. But no, we aren't expanding. I don't know if you've ever heard of Topological quantum field theory, but it's related to knot theory, and offers a nice simple analogy. It's actually back-to-front, and it's shy a dimension or two, but I think it gets it across quite nicely:

Think of space as a big sheet of rubber that's being gently stretched from all sides. Now think of yourself as a knot tied in the rubber. You're bound by some very strong forces. You don't expand.

17. Originally Posted by kojax
What going I'm to say isn't quite mathematically accurate, but it should serve as a sufficient description of what is happening:

Suppose the total distance had been 2 million light years flat when the light was emitted, and in the time it took it to get half way here, the total distance expanded to 2.26 million light years (it wouldn't be that number, because you have to account for the continuousness of it, but I'll use it for simplicity)

That means the light got half way here by traversing 1.13 million miles. In a static (non expanding) universe, it would have to traverse 1.26 million miles to get half way here.
Looking at this again, I got that wrong. If the distance were 2 million flat when the light was emitted, and half way there the total distance became 2.26 million, then that means the light got half way there by going 1 million light years (not 1.13, my mistake.)

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