Size of the Universe?

[Chasteen02]

Hello everyone, I am new to this forum and honestly I have just began to study Physics. I had never really found it interesting until recently. So I am really new to all of this stuff. I hope I do not sound like a complete idiot, but if I do feel free to tell me. I am just here to learn.

 

My question is this,

I have been led to believe that the universe started as a singularity. After the big bang the universe started expanding rapidly. I have also learned that nothing can travel faster than the speed of light. Therefore the universe should not have been able to expand faster than the speed of light. It has been said that the universe is about 14.6 Billion years old.

 

Now to me this means that the radius of the universe should be 14.6 Billion light years. As I looked into this I found that scientist believe the radius of just the observable universe is about 45.7 billion light years. Something doesn't add up here to me. How could the universe have expanded faster than the speed of light?

 

To go a little deeper, Einstein's theory of relativity, consist of spacetime. Stars, planets, etc. could not exist without spacetime. Now, to have spacetime, Time must have been able to reach that part of space. If the speed of light travels father than time, How could time have reached an area of space that is 45.7 Billion light years away? Does this mean that time has been since before the big bang?

 

Please someone help me out with understanding these things.

[Spyman]

We currently don't know how the Universe started out, the singularity is more an indication of the breakdown of current understanding than a indication of how the Universe started, there is no knowledge preventing the Universe from having started out infinite big.

 

In relativity nothing can travel faster than the speed of light through space but space can expand or contract without speedlimits.

 

We have no idea of how big the whole Universe is, but we can calculate how big the observable universe around us is, that is how far expansion have brought objects that we can see.

 

Time like Space is nothing that moves around inside the Universe but is constantly everywhere and have always been there, from the very start.

 

Here are some links for you to read:

 

The Big Bang theory: http://en.wikipedia.org/wiki/Big_Bang

 

Observable Universe: http://en.wikipedia.org/wiki/Observable_universe

 

Metric expansion of space: http://en.wikipedia.org/wiki/Metric_expansion_of_space

[EWyatt]

 

My question is this,

I have been led to believe that the universe started as a singularity. After the big bang the universe started expanding rapidly. I have also learned that nothing can travel faster than the speed of light. Therefore the universe should not have been able to expand faster than the speed of light. It has been said that the universe is about 14.6 Billion years old.

 

 

 

A great question, one that I've asked myself. I'm not sure about the previous reply -- that space has no speed limit when expanding. Then the writer says that space is infinite. Oh well. But as has been explained to me, the time after the initial Big Bang did not operate according to our current laws of physics. Light speed meant nothing then because matter/energy wasn't "finalized" for a very long time to the condition it's now. Therefore, whatever "goop" there was initially could have expanded at MUCH higher speeds that our current light-speed scenario.

 

But who really knows! Scientists and pseudo-scientists say whatever feels good to them. Personally, I don't buy into this "singularity" bit regarding black holes, whereby the core is an infinitely dense point smaller than an atom. Or so. If that singularity is "infinitely dense and small," shouldn't ALL black hole cores have the same gravitational attraction, therefore same accretion disk size?

 

Anyway, keep thinking! Good luck.

 

EW

[UglyIgloo]

According to most cosmological theories, the universe was expanded faster than the speed of light at a very early phase. I'm not sure there would be a way to ever actually know how large the universe is, since we can't ever catch up to it at the speed of light.

 

The universe expanded at a dramatically slower speed after the big bang, making it even harder to find out the present day size of the universe.

[Chasteen02]

Thanks for the feedback. I like the thought that in the early stages of expansion the universe did not operate under the current laws of physics. I am going to look into this more, but it is something that I could see as being a possibility.

[IM Egdall]

Per special relativity, nothing can travel through space faster than the speed of light. But per general relativity, space itself can and does expand faster than the speed of light. According to inflation theory, moments after the big bang, the unverse underwent an exponential expansion faster than the speed of light before it settled down to its current expansion rate.

 

See http://en.wikipedia.org/wiki/Inflation_(cosmology)

 

Plus at a far enough distance from us, from our point of view space right now is expanding faster than the speed of light.

[Spyman]

I'm not sure about the previous reply

What I said and links I posted represents current accepted consensus in modern cosmology, Wikipedia might not be the best of sources but serves well as an initial read and for a basic understanding.

 

 

-- that space has no speed limit when expanding.

The theory of Relativity has so far passed every test made and is now considered a cornerstone of modern physics. As I and others have said it has no speed limit on how fast space can expand:

 

While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such theoretical constraint when space itself is expanding. It is thus possible for two very distant objects to be expanding away from each other at a speed greater than the speed of light, and this is true for any object that is more than approximately 4.5 gigaparsecs away from us.

http://en.wikipedia.org/wiki/Metric_expansion_of_space

 

 

Then the writer says that space is infinite.

I never claimed that "space is infinite", what I said was: "We have no idea of how big the whole Universe is" and "there is no knowledge preventing the Universe from having started out infinite big", you and everyone else can scroll up to my post #2 and check it anytime.

 

 

Oh well.

The Big Bang was not an explosion in space throwing pieces of matter in every direction from a center:

 

The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distance between two comoving points.

http://en.wikipedia.org/wiki/Big_Bang#FLRW_metric

 

An as long as people cling to this old fashion idea in a Newtonian universe they will have a hard time understanding how an infinite universe is able to expand, but with relativity expansion of space is a scalar between our view and our equipment:

 

This metric contains a scale factor, which describes how the size of the Universe changes with time.

http://en.wikipedia.org/wiki/Big_Bang#FLRW_metric

 

Imagine that you are in a universe so huge that you can not see any edges, (it could be infinite), suddenly you and your equipment start to shrink, how do you think that the universe would appear? There is no difference if we shrink or the universe expands, the measurements would be equal and more importantly it doesn't matter if there is an boundary or not, the parts we can see on the inside appears the same whether a boundary exists or not.

 

 

But as has been explained to me, the time after the initial Big Bang did not operate according to our current laws of physics. Light speed meant nothing then because matter/energy wasn't "finalized" for a very long time to the condition it's now. Therefore, whatever "goop" there was initially could have expanded at MUCH higher speeds that our current light-speed scenario.

AFAIK, the Big Bang model does not contain any changes of the laws of physics, and scientist in general assumes that nature doesn't trick them:

 

Underlying assumptions

The Big Bang theory depends on two major assumptions: the universality of physical laws and the cosmological principle. The cosmological principle states that on large scales the Universe is homogeneous and isotropic.

 

These ideas were initially taken as postulates, but today there are efforts to test each of them. For example, the first assumption has been tested by observations showing that largest possible deviation of the fine structure constant over much of the age of the universe is of order 10⁻⁵. Also, general relativity has passed stringent tests on the scale of the Solar System and binary stars while extrapolation to cosmological scales has been validated by the empirical successes of various aspects of the Big Bang theory.

http://en.wikipedia.org/wiki/Big_Bang#Underlying_assumptions

[Widdekind]

Quantum particles of mass-energy, residing in the fabric of space-time, resemble actors, on a stage. The actors can only run across the stage so quickly (speed of light limit); but the stage itself can expand / stretch / grow at any rate. The Hubble Expansion is the latter; the stage is expanding, and carrying the actors (in galactic scale clumps) with the expansion

[EWyatt]

What I said and links I posted represents current accepted consensus in modern cosmology, Wikipedia might not be the best of sources but serves well as an initial read and for a basic understanding.

 

 

etc.........

 

Spyman, thanks for the fine reply and explanations. I learned a lot from that. However, in 75 years, most of what we "know" now may be relegated to what the Dark Age scientists called "fact" then. But maybe not.........

[Airbrush]

...... in 75 years, most of what we "know" now may be relegated to what the Dark Age scientists called "fact" then. But maybe not.........

 

I doubt that "most" of what we know will be disproven. Some of it will. When scientists say they "know" something as a fact, that is more than speculation.

Edited October 2, 2012 by Airbrush