Set me straight: Universe Size & Age = FTL motion?

[Ptrope]

Okay, I'm no astrophysicist, so my insight into the size and age of the universe is just a knee-jerk, gut response to numbers.

While watching a show on the History channel the other night, I happened to catch them as they were talking about the Big Bang, and the size and age of the universe that resulted. The numbers they gave startled me. My assumption would be that the universe's size in light-years would be, at most, 2x its age, given a symmetrical expulsion of matter and the assumption that its ultimate speed could only be a fraction under the speed of light. So if the universe is 13.6 billion years old, at the speed of light, that would put its limits at <13.6 billion light-years from the center of the explosion.

So how is the universe 156 billion light-years across? That would make the minimum required speed for matter to reach the edge (156/2)/13.6, or 5.7*SOL.

As near as I can tell from the explanations online, the 'reason' for the discrepancy is that the expansion of the universe isn't one of distance, per se, but one of scale, that when the universe was smaller, it was also compressed in time/space, and that a particle at the edge of the universe has traveled 78 billion light-years only because the expansion of the universe has continually 'moved the goal posts' since the Big Bang, and that in actuality, it has only traveled 13.6 billion light-years, but light-years have gotten 5.7 times longer since it began its journey.

In essence, this sounds exactly like warp theory to me, that we avoid exceeding SOL by warping the subjective points of the universe closer together and traveling between them at non-relativistic speeds - it sounds like this is exactly what the universe has done, altering the constants of time and space as it expanded.

Do I read this right? Or is it just astrophysicists hemming and hawing around the fact that the universe's size contradicts the theory of relativity?

 

[FrankR]

Yes; you are correct. The expansion of the universe is space/time itself expanding and dragging matter with it.


-frank

 

[All Seeing Eye]

I was under the impression that the speed of light at the beginning of the universe was much faster than it is now due to the immense force of the big bang and that the speed of light slowed down immediately after the big bang when everything calmed down and the universe took shape.

 

[Lindley]

It's kinda like inflating a balloon.

 

[Gepard]

It's kinda like inflating a balloon.

"And then...something bad happens!"

 

[chardman]

I was under the impression that the speed of light at the beginning of the universe was much faster than it is now due to the immense force of the big bang and that the speed of light slowed down immediately after the big bang when everything calmed down and the universe took shape.

The speed of light is a "Universal constant" for a reason. If it changed speed over time, it wouldn't really be constant now would it, let alone universally so, eh? I guess that wasn't in your school's curriculum either?

 

[Shaw]

... So if the universe is 13.6 billion years old, at the speed of light, that would put its limits at <13.6 billion light-years from the center of the explosion.

So how is the universe 156 billion light-years across? That would make the minimum required speed for matter to reach the edge (156/2)/13.6, or 5.7*SOL...

This place is not a good place for discussing real physics... but that having been said, you seem to be suffering from the problem of big bang graphics on TV.

You are at the center of the big bang explosion... and so am I. Everywhere is the center of the explosion and the expansion.

There is no edge. It is like worrying about the edge of the Earth. The Universe has no edge but has a finite volume the same way the Earth has no edge but a finite surface area. The difference is that the volume of the Universe is increasing.

Maybe that will point you in the right direction a little.

 

[All Seeing Eye]

I was under the impression that the speed of light at the beginning of the universe was much faster than it is now due to the immense force of the big bang and that the speed of light slowed down immediately after the big bang when everything calmed down and the universe took shape.

The speed of light is a "Universal constant" for a reason. If it changed speed over time, it wouldn't really be constant now would it, let alone universally so, eh? I guess that wasn't in your school's curriculum either?

Everything was different during the big bang, even the speed of light.

 

[Ptrope]

^
Oh, I realize there's not something like an "edge," but it's a term for the outer limit of the universe's volume. Don't worry - I didn't buy the galaxy's 'edge' from "Where No Man Has Gone Before, Either" .

That being said, though, I don't know that I would agree with the concept that 'everywhere' is the center of the explosion; without a true center, how do we measure 'expansion?'

Spatiotemporal physics make Mongo head hurt ...

 

[Shaw]

That being said, though, I don't know that I would agree with the concept that 'everywhere' is the center of the explosion; without a true center, how do we measure 'expansion?'

By the rate at which everything is moving away from us.

The problem with TV science descriptions of the big bang is that it looks like the explosion happens in a pre-existing volume. There was no pre-existing volume, every point that is now was once at one point.

But no one has to accept anything... but what is great is that physics is way more mind blowing than anything science fiction has to offer. Unfortunately I've reached the conclusion that some ideas are just outside of where some people are secure and comfortable.

But if you want to see what the universe is sorta like, this software might be helpful. It'll show you different topological spaces... none of which have boundaries or edges.

You look into the distance and see... yourself. If you could see the other side of the universe... you'd be looking at the back of your head.

 

[Ptrope]

Just like Land of the Lost

 

[Asbo Zaprudder]

Everything was different during the big bang, even the speed of light.

Perhaps so -- according to a theory by Albrecht and Magueijo, the speed of light may be many orders of magnitude greater at high energies to make the Planck length invariant. It is proposed that this explains the horizon problem (non-causally connected regions of the universe look very similar) and offers a better explanation for cosmic inflation (the initial superluminal expansion of spacetime).

http://arxiv.org/abs/astro-ph/9811018
http://arxiv.org/abs/gr-qc/0007036

Only one theory among many, of couse.

 

[FordSVT]

I was under the impression that the speed of light at the beginning of the universe was much faster than it is now due to the immense force of the big bang and that the speed of light slowed down immediately after the big bang when everything calmed down and the universe took shape.

The speed of light is a "Universal constant" for a reason. If it changed speed over time, it wouldn't really be constant now would it, let alone universally so, eh? I guess that wasn't in your school's curriculum either?

While you were busy poking sticks at Tachy you were too busy to realize that he is correct and you aren't. Or at least, he's correct that is one theory. NONE of this stuff is 100% factual, most of it is based on cosmological observations and a lot of very complicated maths.

 

[chardman]

So you're saying that the speed of light isn't a universal constant but a wholly conditional one?

 

[FordSVT]

We're talking about the early state of the Universe, not the here and now. It's a discussion about why scientists estimate the size of the universe in light years to be much greater in number than the number of years the universe has existed, perhaps you'd like to join it.

 

[chardman]

I'd sure as Hell think that the universal constance (or lack thereof) of a supposed universal constant would be well within the discussion about why scientists estimate the size of the universe in light years to be much greater in number than the number of years the universe has existed. That said, I joined the actual conversation with my very first post. You? Not so much.

 

[FordSVT]

Plain and simple, Tachy made a perfectly reasonable statement, you mocked him, now you're back-peddling. Nice.

 

[chardman]

Uh. No. It's either a UNIVERSAL constant or it's not. Science has accepted that it is universal, so my point stands. And as you yourself stated earlier, Tacky is right about one of many possible theories. I prefer a number of other theories which do not require one to pretend that the universal constant of light-speed isn't/wasn't really universal, but offer other plausible ideas to explain the seemingly FTL expansion of the universe.

 

[All Seeing Eye]

But we're talking about a time when the universe was in the process of being created and was not yet created. How can you have a universal constant at a time when the universe wasn't yet created.
In fact time apparently didn't exist before the big bang and was created at that moment so how can you have universal constants when time (like the physical universe) is in the middle of being created.

How much energy was there in the big bang? do we know how much matter and anti-matter there was? what kind of force was created at the moment of the big bang forcing matter outwards?

 

[B.J.]

From what I understand, the speed of light is still constant, just not in the way you thought it was. Say for instance that you measured the time light takes to get between to points in the universe very early on in the universe's life, and you got t1. Now, many billions of years later, you measure light going between the same two points in the universe. Due to the expansion of *the very fabric of the universe* that light (which is still at a "constant" speed) takes much longer to get between those two points, so t2 >> t1. We, being "in" the universe, see that as the speed of light slowing down, but due to a lot of astrophysics I don't understand, it's really not.

(I really hope I got that right, and didn't just make a fool of myself!)