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What exists beyond the known universe?


Tim_Lou

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Interesting! I am familiar with Pascal and his Wager, which serves more as a REASON to ACCEPT than it does a PROOF of a god. But I have never run into this one before. A quick Google did not find anything. Could you provide a link/ some details?

 

Hmm you're right it was the wager of pascal... I dont remember in that case who gave the god proof i told... my reference is my history teacher, who told it about 10 years ago...

(in september i have a reuniun of my high school, i will ask him )

 

Bo

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Uncle Martin: OK Jethro, I think you may have smoked one too many crawdads.

 

If you flip a coin 10^9 th times and it comes up heads every time, the probability of heads or tails the next flip is still 50%.

 

I disagree. If you flip a coin one billion times and it comes up heads every time, the coin is NOT a fair coin...it is weighted or otherwise biased to land heads. We know this because the probability of a fair coin coming up heads one billion times in a row is 1 in 2^1,000,000,000. Therfore, one should predict that the probability of its coming up heads in the next toss is virtually 1.

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Originally posted by: Uncle Martin

OK Jethro, I think you may have smoked one too many crawdads.

Could never figure out which end to light!

If you flip a coin 10^9 th times and it comes up heads every time, the probability of heads or tails the next flip is still 50%. Are you maybe applying the quantum world to the macro world? Or are you implying that probability will eventually even out? I don't think it *must* reach equillibrium.

My bad! You're correct!

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Originally posted by: Bo

Hmm you're right it was the wager of pascal... I dont remember in that case who gave the god proof i told... my reference is my history teacher, who told it about 10 years ago...

Ya, blame someone else! :-)

 

Had me worried for a while. I have spent some time researching Pascal, particularly involving his "Wager". Did not run into what you had said, before.

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It seems implausible that the universe is infinite, because the matter in the universe is almost certainly finite.

 

Consider. If there was an infinite number of stars then there would be a star in every direction we looked, with no space between. It would be a furnace, and we would be cooked.

 

There are various arguments against this roasting sky argument, but they don't hold water:

 

1) The more distant stars are travelling away from us so fast that their light is red shifted to effectively nothing.

 

This argues that all matter came from the big bang, a finite amount. We then have a tiny patch of matter in an infinite universe. Could the conditions that created the big bang exist in one place, and only one place, in so large a space? It hardly seems possible, and yet the only plausible alternative would be an infinite number of big bangs. In that case as many of these distant stars, from other big bangs, would be travelling towards us, as away.

 

2) Most of the light is shielded by dark matter.

 

No go. The dark matter would just heat up to the same temperature as the stars and re-radiate the light.

 

3) The universe, or at least the matter in the universe, is too young for the light from these distant stars to have arrived.

 

Possible, but that postulates a universe infinite in size, but not time. Given that time is no more than another dimension, it seems unlikely. The big bang (if that was indeed the start of our, er, local mater entering the universe) has a definite starting time, but that assumes only one big bang. If there are an infinite number of them, they must have been starting at different times, right back to infinitely far in the past.

 

 

I vote for a finite universe, which curves back on itself. That way you don't have an edge to the universe any more than there is an edge to the world. Travel far enough and you just get back to the beginning.

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Originally posted by: BlameTheEx

I vote for a finite universe, which curves back on itself. That way you don't have an edge to the universe any more than there is an edge to the world. Travel far enough and you just get back to the beginning.

 

The best explanation I have seen so far is the balloon analogy. Imagine a balloon deflated to a single spot, the point of the BB. From this point the balloon begins to expand in all directions as balloons do. The universe is the SURFACE of the balloon. Thus all points on the balloon expand away from each other based on their distance from each other. The surface is curved, but the curvature is less noticable the more it has expanded.

 

Thus a particle/ person/ ... could travel for an infinite time and never reach an end.

 

We would also see the universe exactly as we do see it today.

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Why is the sky is dark at night? Because the speed of light is finite, not infinite.

 

During the fraction of a second that inflation occurred, the Universe expanded exponentially, faster than c. Therefore, even though the Universe is only about 13 billion years old, and even if we don't take superluminal movement of very distant galaxies into consideration, there are stars out past the 13-billion lightyear distance. We can't see those stars - with only 13 billion years of travel, their light has not had time to travel the distance from them to us.

 

So there could be a thousand, a trillion, an octillion, a googol, or any number of stars in the Universe and the sky would still be dark at night. But if the speed of light were infinite, then their light would be reaching us already and we would be cooked at "night".

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Is "cooked" the right word? A very small percentage of known stars are visible to the unaided eye, not because the light hasn't had time to reach us yet, but because of the absorbtion and deflection by interstellar gas and debris. And our own atmosphere of course. If c was infinite we would see infinitely using telescopes and other detection devices, but I don't think we would notice a difference with our eyes, and we wouldn't be doing away with all our light bulbs.

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The assumption being countered is that every line of sight should intersect a star. Thus, everywhere you look in the sky photons would be streaming into your eye, even at "night" (i.e., when the sun is on the other side of the Earth). The sky should be blazing bright 24 hours a day...more blazing even so than a day when the sun is directly overhead and there is no shade, because everywhere in the sky - all points in all directions - would be as bright as the sun (in actuality, the sun covers only a very small fraction of the sky we see). If the assumption were correct, then the term "cook" would be pretty appropriate.

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Originally posted by: TeleMad

The assumption being countered is that every line of sight should intersect a star.

Virtually every line of sight does. Hubble has very few openings to get a truly clear view of the most distant galaxies.

Thus, everywhere you look in the sky photons would be streaming into your eye, even at "night" (i.e., when the sun is on the other side of the Earth).

They are, just a small percentage of them are in our visual spectrum. On a cosmic scale, day and night are rather meaningless, aren't they. There are stars in the sky during the daylight hours, we just don't see them because our atmosphere is brighter than they.

The sky should be blazing bright 24 hours a day...more blazing even so than a day when the sun is directly overhead and there is no shade, because everywhere in the sky - all points in all directions - would be as bright as the sun (in actuality, the sun covers only a very small fraction of the sky we see). If the assumption were correct, then the term "cook" would be pretty appropriate.

Which we agree is false? I know we are both arguing Blame's proposal, I just wanted to clarify a few things. And yes, IF the assumption were true, or our atmosphere was less dense or of a slightly different composition,...cooked would be an appropriate term.

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Originally posted by: TeleMad

Why is the sky is dark at night? Because the speed of light is finite, not infinite.

........So there could be a thousand, a trillion, an octillion, a googol, or any number of stars in the Universe and the sky would still be dark at night. But if the speed of light were infinite, then their light would be reaching us already and we would be cooked at "night".

This I disagree with. If c. was infinite, (strange concept) photons would travel any distance instantly. We would be able to see further, using detection devices other than our eyes, but I don't think an infinite number of photons would reach us. There is alot of matter between us and infinity to stop most of the photons that would reach us undisturbed. We would likely "see" further and a bit more, but I don't think things would be all that different. Even if c was infinite, the sky would still be dark at night.

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Okay, first about the "cooking" part and the general question being asked, "Why is the sky dark at night?".

 

"In a universe of infinite extent, populated everywhere with bright stars, the entire sky should be covered by stars with no separating dark gaps. Hence, when all stars are bright like Sun, the entire sky at every point should blaze with a brilliance equal to the Sun's disk. The sky is 180,000 times larger than the Sun's disk, and starlight falling on Earth should be 180,000 times more intense than sunlight. In the midst of this inferno of intense light, life would cease in seconds, the atmosphere and oceans boil away in minutes, and the Earth turn to vapor in days. Fortunately, the sky at night is dark." (Cosmology: The Science of the Universe: Second Edition, Edward Harrison, Cambridge University Press, 2000, p491-492)

 

 

As far as part of your solution, that some of the light being absorbed on the way would prevent the “bright-sky at night” and associate “cooking”…

 

”Of course, if considerable absorption occurs, as Cheseaux and Olbers said, then most lines of sight terminate on dust grains and other absorbing particles. But because the absorbing particles heat up and then emit as much radiation as they absorb, the sky will be as bright as with no absorbing particles.” … Absorption of starlight in interstellar space cannot avert a bright sky. It is as ineffective as putting an absorbing gas into a furnace in the hope that it will keep the objects inside cool. The gas quickly heats up to the same temperature as the furnace and nothing is gained. Whatever is put in a bright-sky universe to shield us from the blinding rays of zillions of stars rapidly heats up and becomes part of the inferno.” (Cosmology: The Science of the Universe: Second Edition, Edward Harrison, Cambridge University Press, 2000, p497-498)

 

The explanation for not having a "bright night sky" is that the speed of light is finite, not infinite. If c were infinite, then in the assumed infinite universe the sky everywhere, all the time, would be ablaze and we would be "cooked" (neither light interacting with gas clouds nor with our atmosphere can avoid this).

 

PS: Came back to add that I just found this after skimming a bit further.

 

”Darkness of the night sky is due not to absorption of starlight, not to hierarchical clustering of stars, not to the finiteness of the universe, not to expansion of the universe, and not to many other proposed causes. The explanation is quite simple and can be stated in various equivalent ways. Because of the finite luminous age of stars and the finite speed of light, the number of visible stars is too few to cover the entire sky; most stars needed to cover the sky are so far away that their light has not reached us; the light-travel time from the most distant stars is greater than their luminous lifetime; …” (Cosmology: The Science of the Universe: Second Edition, Edward Harrison, Cambridge University Press, 2000, p505-506)

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TeleMad: The assumption being countered is that every line of sight should intersect a star.

 

Uncle Martin: Virtually every line of sight does. Hubble has very few openings to get a truly clear view of the most distant galaxies.

 

There is plenty of dark space in the Hubble pictures of the deep field.

 

Also, telescopes that compete with our eyes can "See" more stars because they collect more photons than our eyes do. Why? Because their lenses are larger than ours and a larger lens covers more area - therefore intercepting more photons. So even if HST did see a star everywhere in the sky (which we both agree it doesn't), that still wouldn't mean that our smaller eyes would.

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TeleMad: Why is the sky is dark at night? Because the speed of light is finite, not infinite. ........So there could be a thousand, a trillion, an octillion, a googol, or any number of stars in the Universe and the sky would still be dark at night. But if the speed of light were infinite, then their light would be reaching us already and we would be cooked at "night".

 

Uncle Martin: This I disagree with. If c. was infinite, (strange concept) photons would travel any distance instantly. We would be able to see further, using detection devices other than our eyes, but I don't think an infinite number of photons would reach us. There is alot of matter between us and infinity to stop most of the photons that would reach us undisturbed.

 

True, but as pointed out in something I quoted above from the Cosmology text, that matter would then heat up to the point that it too would radiate light, thus canceling its ability to reduce the amount of light reaching us. So if c were infinite then the sky would be ablaze even at night.

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Originally posted by: TeleMad

True, but as pointed out in something I quoted above from the Cosmology text, that matter would then heat up to the point that it too would radiate light, thus canceling its ability to reduce the amount of light reaching us. So if c were infinite then the sky would be ablaze even at night.

 

OK, I did some reading on this and now see what you are saying. It seems to me that the expansion of the universe combined with the speed of light being what it is,...is the reason for the ultimate cooling of the universe, rather than heating. If c was infinite all photons would be everywhere at one instant in time and all matter would likely cease to exist?

 

186,000 mps is plenty fast.

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Yes, that's one reason. Another reason is that even earlier, the Universe was opaque. There was a time before stars began forming - about 300,00 (or is it 500,00) years after the Big Bang - when recombination occurred. During this time, at the point when energies fell low enough, free electrons fell into stable orbits around protons to form atoms. At that point, the Universe became transparent to light. So we really can't hope to see back all the way to Big Bang..

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