How did Earth get so far away from other galaxies?

[Gaylan Larson]

TL;DR Summary

How can the James Webb telescope see 13.3 billion years into the past when the universe is only 13.6 billion years old?

If the Big Bang happened 13.6 billion years ago how can the James Webb telescope now see galaxies 13.3 billion light years away? 13.3 billion years ago the universe was 0.3 billion years old. How large was the universe at that time? If physical mater traveled in all directions from the point of the big bang at light speed for 0.3 billion years, the longest distance between the edges of the universe would be 0.6 billion light years. The light that the James Webb telescope is seeing that came from those galaxies had to travel 13.3 billion light years to get here. That means the mater that became earth, if it was at the opposite edge of the universe from the light emitting galaxies, had to travel at least 12.7 billion light years (13.3-0.6) in 13.3 billion years in order to keep ahead of the light so that it could detect it here, now. How is that possible? Did the light take a slower route?

 

[PeroK]

The early universe went throgh a period of inflation:

https://en.wikipedia.org/wiki/Inflation_(cosmology)

There is no limit to the speed at which space itself can expand. Two points in space can recede from each other greater than the speed of light.

 

[Ibix]

The Big Bang happened everywhere; it's not an explosion from a point, although it is unfortunately often described as such. So there are galaxies 13bn light years away and there always have been since galaxies formed.

You also need to be careful with what people mean when they tell you how far away things "are". Do they mean how far away they were when the light we receive was emitted, or how far away they are now, or how long the light has been travelling? People aren't always clear which they mean when they aren't talking in professional journals.

Anyway, the point is that the universe has always been filled more-or-less uniformly with matter, so there's no particular surprise in seeing very old stuff in every direction. I think people are surprised to see galaxies forming quite so early, that's all.

 

[Gaylan Larson]

Thank you Perok and Ibix,
Just so I understand your statement, Perok, you're saying that travel faster than the speed of light is possible for the universe, is that correct.

 

[Frabjous]

Do they mean how far away they were when the light we receive was emitted, or how far away they are now, or how long the light has been travelling?

At what distance does the distinction become meaningful?

 

[Ibix]

Thank you Perok and Ibix,
Just so I understand your statement, Perok, you're saying that travel faster than the speed of light is possible for the universe, is that correct.

Not exactly. However, the rule that things cannot exceed the speed of light turns out to have limitations. It is true that nothing can ever overtake a light pulse, not ever. But the "expanding space" concept means that distance grows pver time, and that means that the distance between two very distant objects can grow arbitrarily quickly.

At what distance does the distinction become meaningful?

Any distance. If you stand on the roadside and I stand on a truck and throw a ball to you a second after the truck passes you then you can ask how far away the truck was when I threw the ball or when you caught it, or how long the ball was in flight.

 

[Gaylan Larson]

When the light was emitted the galaxies as where the relative position of the James Webb telescope would have been was 0'6 billion light years apart if they were on opposite sides of the resulting Big Bang. That is the position of the galaxies when the light was emitted. The light has been travelling from that point for 13.3 billion years and the location of the James Webb telescope has presumable kept ahead of the traveling light so as to intercept it now. But other posts are telling me I'm over simplifying light speed, recession velocity, things that are way over my head. No wonder it isn't making much sense to me.

 

[Orodruin]

The early universe went throgh a period of inflation:

https://en.wikipedia.org/wiki/Inflation_(cosmology)

There is no limit to the speed at which space itself can expand. Two points in space can recede from each other greater than the speed of light.

Inflation is irrelevant to the question at hand though. Galaxies did not form until long after inflation.

What is true is that the distance between two comoving objects can grow faster than the speed of light.

Thank you Perok and Ibix,
Just so I understand your statement, Perok, you're saying that travel faster than the speed of light is possible for the universe, is that correct.

Nothing is travelling faster than the speed of light. The space in between the objects is growing — making the distance between them increase faster than the speed of light.

 

[Ibix]

on opposite sides of the resulting Big Bang

No such thing. As I said before, the Big Bang was everywhere, not an explosion from a point.

 

[Frabjous]

Any distance. If you stand on the roadside and I stand on a truck and throw a ball to you a second after the truck passes you then you can ask how far away the truck was when I threw the ball or when you caught it, or how long the ball was in flight.

Sorry, I wasn’t clear. At what distance does one need to take inflation expansion into account when doing calculations?

corrected

 

[Ibix]

But other posts are telling me I'm over simplifying light speed, recession velocity, things that are way over my head. No wonder it isn't making much sense to me.

The maths is very involved, but a limited analogy is possible. Get a rubber band and a ruler and a pen. Pull the rubber band enough that it's straight but not stretched and use the ruler and pen to mark a row of dots 1cm apart on the rubber. Now get an ant and put it on the rubber band on one dot and let it start walking. At that instant you know the distance between two dots. Start stretching the rubber band as the ant walks. When it reaches the next dot you can say that the dots on the band are further apart and the ant walked more than 1cm because the distance between it and the next dot grew while it was walking.

The dots are galaxies and the ant is light travelling through space.

Don't take this analogy too seriously - it has some serious shortcomings. But it does illustrate nicely how distance now, distance then, and the distance walked may be different things.

 

[Ibix]

Sorry, I wasn’t clear. At what distance does one need to take inflation into account when doing calculations?

Inflation? Never. It ended at the Big Bang. The continuing expansion of space is a different phenomenon.

The answer depends where you are and how much precision you need. In an idealised perfectly isotropic spacetime then expansion is (in principle) detectable at any distance above zero, although you can ignore it for small distances and times if you don't need too much precision. In the real world expansion is detectable at a few tens of megaparsecs if I remember correctly. You just need to look beyond the local group, which is gravitationally bound and doesn't expand. But, again, it depends how much precision you need when you need to start worrying about it.

 

[PeroK]

Thank you Perok and Ibix,
Just so I understand your statement, Perok, you're saying that travel faster than the speed of light is possible for the universe, is that correct.

Not in those terms. The expansion of space itself means that distant objects may recede from each other faster than light.

The important point, however, is that the expansion of space means that light takes longer to travel from A to B than the initial distance between A and B. And, by the time it reaches B, point A might be even further away that the light travel time multiplied by the speed of light.