[Chrismalta]

Christopher Bianco  asked the Naked Scientists:

Today I came across this report about an explosion originating near the edge of the universe, seen by an orbiting NASA telescope.  The burst of gamma rays is the farthest such event ever detected.

I just can't understand the edge of universe? Does the universe has a real edge and what's beyond it??

Thanks
Chris Bianco from Malta

What do you think?

[JP]

They probably meant the edge of the visible universe.  Since light travels at a finite speed, it can only have traveled a certain distance in the 14 billion years the universe has been around.  The light which can reach us defines a giant sphere (radius = 14 billion parsecs) around the earth.  If something is further away than that, its light won't have reached us yet. 

Since light-speed is the speed limit for everything in the universe, nothing from beyond this region will have reached us yet, and so we don't know what's beyond it.  Most scientists tend to believe in the cosmological principle, which says that the universe is pretty much the same everywhere, at least on large scales.  Therefore, it should be basically the same outside our visible universe as it is inside. 

There's a lot more details here: http://en.wikipedia.org/wiki/Observable_universe

[socratus]

They probably meant the edge of the visible universe.  Since light travels at a finite speed, it can only have traveled a certain distance in the 14 billion years the universe has been around.  The light which can reach us defines a giant sphere (radius = 14 billion parsecs) around the earth.  If something is further away than that, its light won't have reached us yet. 

Since light-speed is the speed limit for everything in the universe, nothing from beyond this region will have reached us yet, and so we don't know what's beyond it.  Most scientists tend to believe in the cosmological principle, which says that the universe is pretty much the same everywhere, at least on large scales.  Therefore, it should be basically the same outside our visible universe as it is inside. 

There's a lot more details here: http://en.wikipedia.org/wiki/Observable_universe

=====================

Does the universe have a real edge and what's beyond it??

=========================.
Let us suppose that the universe is “a giant sphere
(radius = 14 billion parsecs) around the earth. “
Is it possible to universe to be “a giant sphere
(radius = 14 billion parsecs) around the earth. “ ?
NO !!! Why?
Because the detected material mass of the
 matter in the Universe is so small  (the average density
of all substance in the Universe is approximately
 p=10^-30 g/sm^3) that this mass cannot turn the universe
 into sphere. So, the Universe as whole is flat infinite space.
Then we have question:
“  Does infinity space have any physical parameters?”
My answer is : “ Yes, the Infinite Universe has one
physical parameters. It is T=0K. Because after “ big bang”,
we must take in calculation that T=2,7K expands and therefore
 T=2,7K is temporary parameter and with time it will go to T=0K.
========================.

[DoctorBeaver]

Correct in principle; but aren't the maths a bit awry? 1pc = 3.26 light years. Therefore the edge of the visible universe is 14billion/3.26 parsecs, not 14 billion parsecs.

Socratus - I assume your 2.7K refers to the CMBR. Surely, that can't ever reach 0K as that would imply zero energy level and QM says that is impossible.

[JP]

Correct in principle; but aren't the maths a bit awry? 1pc = 3.26 light years. Therefore the edge of the visible universe is 14billion/3.26 parsecs, not 14 billion parsecs.

The extra distance is due to the expansion of the universe.  I didn't discuss that detail since it's a bit tricky to grasp.  The light has been traveling at c, but the space between us and those distant stars has stretched.  Your numbers are right if the universe is static.

[socratus]

Socratus - I assume your 2.7K refers to the CMBR. Surely, that can't ever reach 0K as that would imply zero energy level and QM says that is impossible.

==============================

Classic physics says that we can't reach 0K.
We can’t reach T= 0K !!!
But not the Nature ( micro particles ) itself !!!
The Nature ( micro particles )  can reach T= 0K !!!

Therefore Quantum theory says that vacuum ( even T= 0K )
is continuum with NO Zero Energy level !!!
That is reason that “ virtual particles “ can exist in Vacuum.
And QT says that from these “ virtual particles “ the real particles
can be born.
==============.

[DoctorBeaver]

Correct in principle; but aren't the maths a bit awry? 1pc = 3.26 light years. Therefore the edge of the visible universe is 14billion/3.26 parsecs, not 14 billion parsecs.

The extra distance is due to the expansion of the universe.  I didn't discuss that detail since it's a bit tricky to grasp.  The light has been traveling at c, but the space between us and those distant stars has stretched.  Your numbers are right if the universe is static.

Are you sure about that? 3.26 light years is 3.26 light years. If 2 objects are 3.26 light years apart and the space between them expands, then they are now more than 3.26 light years apart. A parsec is still 3.26 light years.

Having it the way you stated would be like having an elastic ruler. You could stretch it and measure 3cm, but it wouldn't really be 3cm, it would be more.

[JP]

I'm not sure I follow you.  What I was trying to get across was that if the universe wasn't expanding, the furthest things we could see would be 14 billion light years away.  The numbers I give are answers to the question, "How far away from us (currently) is the most distant object we can see?"  In a universe that wasn't expanding, the answer would be 14 billion light years.  However, since the universe is expanding as the light is traveling, the space between us and that object has expanded since it emitted that light, and so it is actually 46 billion light years (14 parsecs) away. 

[DoctorBeaver]

Let's see if I understand you correctly. What you are saying is that although the light we see was emitted 14 billion years ago, the object that emitted it is now 42 billion light years away due to the expansion of the universe. Is that what you mean?

[JP]

Yes, that's basically it.

[DoctorBeaver]

OK. I misunderstood at first.

[LeeE]

Heh - yeah - the furthest stuff we can see is now ~42 billion light years away, but the photons we see only originated ~13-14 billion light years away.  Of course, they ended up traveling a lot further than that to reach here, so it depends on how you define it - it could be the distance between us and (a) the object's current distance, (b) the object's original distance, or (c) just the total distance traveled by the photon []

[DoctorBeaver]

LeeE - Stop confusing the issue even more!  []

[lyner]

jp

46 billion light years (14 parsecs) away.

??
1pc is only 3.26ly, actually. You mean 14 billion pc, I think.

[JP]

jp

46 billion light years (14 parsecs) away.

??
1pc is only 3.26ly, actually. You mean 14 billion pc, I think.

Yeah, I dropped a billion somewhere.  Good catch.

[DoctorBeaver]

PAH... what's a billion here & there between friends!

[lyner]

14 or 14 billion: you'd be no nearer to the edge.

[socratus]

1.
quote author=DoctorBeaver

PAH... what's a billion here & there between friends!
2.
quote author=sophiecentaur

14 or 14 billion: you'd be no nearer to the edge.
=========.
Nice.
It only remains to understand what infinity is.
=====================

[lyner]

We've a long way to go yet.

[socratus]

We've a long way to go yet.

==================

It is pity.  Is our intellect really so poor ?

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