Big Bang and the speed of light

[Alpinestars]

Noddy question about the speed of light and the Big Bang.

Just listening to 5 live this morning and a caller asked how we, at the "edge" of the Big Bang are able to look back to its origin. The "expert" explained that we were all part of the Big Bang in that everything was at the same place? and the Big Bang caused an expansion of space and therefore created distance between objects. We can now look back, I assume at things that didn't expand as quickly?? I must have that wrong, because wouldn't that mean we would have travelled faster than the speed of light to be able to look back at things which are billions of years old (via the light they emitted billions of years ago)?

Hope that makes sense?

What have I misunderstood?

Thanks

[Einion Yrth]

Alpinestars said:

Noddy question about the speed of light and the Big Bang.

Just listening to 5 live this morning and a caller asked how we, at the "edge" of the Big Bang are able to look back to its origin. The "expert" explained that we were all part of the Big Bang in that everything was at the same place? and the Big Bang caused an expansion of space and therefore created distance between objects. We can now look back, I assume at things that didn't expand as quickly?? I must have that wrong, because wouldn't that mean we would have travelled faster than the speed of light to be able to look back at things which are billions of years old (via the light they emitted billions of years ago)?

Hope that makes sense?

What have I misunderstood?

Thanks

You haven't considered Alan Guth's inflationary theory.

[Alapeno]

This is as basic as it comes I think, someone will probably be along to expand on this.

Inflation theory says that Space actually expanded rather than objects moving at relative speed and distance to one another. A basic way of looking at it is to draw 2 dots on a balloon and then inflate it. The dots haven't moved from their original position in space (on the ballon) but the space between them has.

Hopefully that makes a little bit of sense.

ETA - think of space as the material that makes up the balloon in 2D (the rubber) rather than the air inside. Then apply that to 3D and you'll get the idea.

Edited by Alapeno on Friday 12th February 09:38

[Alpinestars]

Alapeno said:

This is as basic as it comes I think, someone will probably be along to expand on this.

Inflation theory says that Space actually expanded rather than objects moving at relative speed and distance to one another. A basic way of looking at it is to draw 2 dots on a balloon and then inflate it. The dots haven't moved from their original position in space (on the ballon) but the space between them has.

Hopefully that makes a little bit of sense.

ETA - think of space as the material that makes up the balloon in 2D (the rubber) rather than the air inside. Then apply that to 3D and you'll get the idea.

Edited by Alapeno on Friday 12th February 09:38

That's helpful.

Did the space expand quicker than the speed of light? Which still takes me back to my original confusion. Ie, what's the relationship between the expansion and the speed of light? To a layman like me, it seems as if light got "left behind". Otherwise I can't reconcile that everything started in the same place, or came to being in the same place, expansion created the distance, but light from the earlier objects (ones where expansion didn't create the same distance?) is still observable. If speed is limited to the speed of light, how can we look back at light?

I'm probably not articulating it well but hopefully someone understands my ramblings.

[Toltec]

Alpinestars said:

That's helpful.

Did the space expand quicker than the speed of light? Which still takes me back to my original confusion. Ie, what's the relationship between the expansion and the speed of light? To a layman like me, it seems as if light got "left behind". Otherwise I can't reconcile that everything started in the same place, or came to being in the same place, expansion created the distance, but light from the earlier objects (ones where expansion didn't create the same distance?) is still observable. If speed is limited to the speed of light, how can we look back at light?

I'm probably not articulating it well but hopefully someone understands my ramblings.

No

Light is not independent of spacetime, the limit of the observable universe is where light would take the entire age of the universe to reach us. I have somewhat of a grasp on this, but clearly do not really understand it properly as I cannot really explain it to you, sorry.

[Thorodin]

Toltec said:

No

Light is not independent of spacetime, the limit of the observable universe is where light would take the entire age of the universe to reach us. I have somewhat of a grasp on this, but clearly do not really understand it properly as I cannot really explain it to you, sorry.

So, and this is (to me) a puzzler, where in the universe are we compared to other significant objects? On an edge, the other edge, in the middle? Is everything getting further away from everything else and travelling at the same speed? Do all objects travel at speeds dependent on their relative mass?

[Halmyre]

Thorodin said:

Toltec said:

No

Light is not independent of spacetime, the limit of the observable universe is where light would take the entire age of the universe to reach us. I have somewhat of a grasp on this, but clearly do not really understand it properly as I cannot really explain it to you, sorry.

So, and this is (to me) a puzzler, where in the universe are we compared to other significant objects? On an edge, the other edge, in the middle? Is everything getting further away from everything else and travelling at the same speed? Do all objects travel at speeds dependent on their relative mass?

If you go back to the balloon analogy, no point on the surface of the balloon can be said to be at an edge or in the middle. It's the same in our 3D universe, with the implication that, if we travel far enough in a straight line, we'll end up back where we started.

Again with the balloon, if it's expanding then the more distant parts of the surface appear to be moving away faster than nearby parts, but they're not really travelling, everything is staying in place relative to each other. There are localised variations where things really are moving, e.g. the Andromeda galaxy is moving towards us, but that's a different matter to expansion.

Speed of 'travel' is independent of mass.

[Thorodin]

Thanks, fascinating. Have to say it provokes even more questions - that's science I suppose. Like: doesn't the balloon analogy suggest that all objects are on the 'outside' of the balloon with nothing in the middle? Apologies for ignorance, I have an abundance of agricultural skills - strictly Earth-bound but gazing upwards and pondering.

[Moonhawk]

This image explains the expansion quite well - and why no matter which galaxy you chose - all others appear to be moving away.

You have two grids of dots (the dots represent galaxies). The red grid is the same as the white grid but has expanded over time.

Take two galaxies on the grid (one with a blue dot and one with a green dot). No matter which galaxy you chose as the centre of the overlay of the grids - all the other dots appear to expand away from it. Although two dots close to the centre of the grid have been chosen here - you would get the same effect no matter which dot you chose.

[tight fart]

Is it possible that the physics of the very large, the universe. Work the same as the very small, an atom?
The more I hear about atoms with particles whizzing around each other the more they sound like space on a large scale.
A scientist on the other day was talking about something so small it could pass through the planet earth without hitting another atom, I could only draw the comparison of something traveling through space.

[Alpinestars]

I still don't understand if space expanded quicker than the speed of light.

[Gnits]

Speed is a measure of moving from point A to point B over a period of time (the classic distance, speed, time relationship). In this case the 'edge' of the Universe is point A and there is no point B. It is not a moving front of stuff moving into or through other stuff.
It is bonkers but the question doesn't really make sense.
Kind of like asking what colour hair 'bald' is.

[Halmyre]

Alpinestars said:

I still don't understand if space expanded quicker than the speed of light.

According to theory, yes, shortly after the big bang it goes through a period where it expands faster than light. It's the reason why the universe is lumpy (i.e. has structure), like overheating a beurre blanc; it splits and curdles.

[Alpinestars]

Halmyre said:

According to theory, yes, shortly after the big bang it goes through a period where it expands faster than light. It's the reason why the universe is lumpy (i.e. has structure), like overheating a beurre blanc; it splits and curdles.

Wow. So something did travel quicker than the speed of light? What was that something and why are we no (theoretically and practically) limited to the speed of light?

[davepoth]

Alpinestars said:

Halmyre said:

According to theory, yes, shortly after the big bang it goes through a period where it expands faster than light. It's the reason why the universe is lumpy (i.e. has structure), like overheating a beurre blanc; it splits and curdles.

Wow. So something did travel quicker than the speed of light? What was that something and why are we no (theoretically and practically) limited to the speed of light?

Travelled faster than the speed of light now and here. In areas of extreme gravity both the concepts of metres and seconds become a bit flaky, and we'd expect extreme gravity at the point of the big bang.

[Thorodin]

Moonhawk said:

This image explains the expansion quite well - and why no matter which galaxy you chose - all others appear to be moving away.

You have two grids of dots (the dots represent galaxies). The red grid is the same as the white grid but has expanded over time.

Take two galaxies on the grid (one with a blue dot and one with a green dot). No matter which galaxy you chose as the centre of the overlay of the grids - all the other dots appear to expand away from it. Although two dots close to the centre of the grid have been chosen here - you would get the same effect no matter which dot you chose.

Thanks, huge help. Trying to get my 'taters in a row! As the overriding force is assumed to be gravity (attraction), what counter effect does centrifugal (expulsion) force have? Does it merely balance things out?

(apologies to OP, shan't go off thread again)

[Alpinestars]

davepoth said:

Travelled faster than the speed of light now and here. In areas of extreme gravity both the concepts of metres and seconds become a bit flaky, and we'd expect extreme gravity at the point of the big bang.

Sorry I still don't understand. If both the Earth and say a distant star started in the "same" place. How did expansion create space between light emitted bu the star and the Earth, when both the Earth and light were subject to the same extreme gravity? Did it only act on matter (Earth) and not on light? I know we can't recreate Big Bang, but can extreme gravity not be created on a small scale to show expansion taking place quicker than the speed of light?

Apologies if I'm being slow.

[davepoth]

Alpinestars said:

Sorry I still don't understand. If both the Earth and say a distant star started in the "same" place. How did expansion create space between light emitted bu the star and the Earth, when both the Earth and light were subject to the same extreme gravity? Did it only act on matter (Earth) and not on light? I know we can't recreate Big Bang, but can extreme gravity not be created on a small scale to show expansion taking place quicker than the speed of light?

Apologies if I'm being slow.

You aren't being slow - Anyone who announces that they fully understand it doesn't really understand it at all; even Stephen Hawking makes it up as he goes along.

The answer to that question is really that nobody is entirely sure. Hopefully further study of gravitational waves will lead us to some more information about what happened at the creation of the universe, bearing in mind that the Big Bang still hasn't been proven.

[Alpinestars]

davepoth said:

You aren't being slow - Anyone who announces that they fully understand it doesn't really understand it at all; even Stephen Hawking makes it up as he goes along.

The answer to that question is really that nobody is entirely sure. Hopefully further study of gravitational waves will lead us to some more information about what happened at the creation of the universe, bearing in mind that the Big Bang still hasn't been proven.

Thanks. No idea what made me think of the question in the first place!

[Toltec]

Alpinestars said:

Sorry I still don't understand. If both the Earth and say a distant star started in the "same" place. How did expansion create space between light emitted bu the star and the Earth, when both the Earth and light were subject to the same extreme gravity? Did it only act on matter (Earth) and not on light? I know we can't recreate Big Bang, but can extreme gravity not be created on a small scale to show expansion taking place quicker than the speed of light?

Apologies if I'm being slow.

It is a matter of scale, the Hubble constant* gives a figure for the expansion of the universe about 70km/s per Mega parsec.

A parsec = 3.26 light years.

Doing a bit of arithmetic it comes out at about 700km/year per lightyear

The earth is 0.00001581 light years from the sun so this is an expansion of about 10 metres per year.

Not quite an answer to your question, more of an illustration that this stuff happens on cosmic not human scales.

* It isn't exactly constant, but that is a different discussion...