How the Universe Ends

[Speakpigeon]

I presume you meant to say r^2. What you're missing is that the number of stars in such a shell goes up at r^2 also.

That would be dependent of the actual density of stars in this infinite universe and more generally whether all lines of sight would be occupied by stars, or whether all those stars would emit at least some energy, etc. The universe could be infinite either without an infinity of stars, or with an infinity of stars spread around in a way that wouldn't light up all the sky at night or with an infinity of stars but only a finite number of them emitting some energy. There could be also situations where the topology of the universe would keep the light from spreading to the whole universe. Also, the universe could be infinite but with a beginning, in which case you would only see the stars that are close enough to us consistent with our sky at night. Also, if you have an infinite universe that keep expanding, the light coming from distant stars won't ever reach us. Same result, our sky at night.

And the light of distant stars would be outside the visible spectrum. No bright sky.
EB

 

[Speakpigeon]

Light looses energy through scattering and absorption resulting in heat.

Scattering doesn't lose energy. Absorption does--but heats up whatever absorbed it. That's why all non-stellar bodies in time get heated to stellar temperatures and thus vaporize.

More likely, absorbed light is re-emitted at lower frequencies, say infrared. So, it won't be visible light and therefore no bright sky to the human eye. Only deep-fry cooking.
EB

 

[Speakpigeon]

We assume that over infinite time photons will not loose energy.

True--but you'll have to throw out a lot of physics if that's not true.

Not necessarily. We could have just enough to make the problem disappear without affecting current measurements. Photons maybe loose energy after a very, very long time. If the density of stars is low enough, no bright sky.
EB

 

[Speakpigeon]

And finally, maybe ET is siphoning off photons to another universe as an energy source.

Again, Occam's razor.

So there's only a paradox if you assume the universe is as (some) scientists assume it is.

So, where's the problem already?
EB

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Superpostion applies. At the plane of the Earth the enrgy per square meter will be the linear sum of the energy of all stars individualy by inverse square.

Scattering is a loss in terms of the enrgy reaching the Earth. As distance increases nergy at Erath from very distant stars will be below threshold detection.

Hubble Deep Field. Hubble on successive passes on a visually dark region adding up photons. There were a lot of objects. Which is my point, the limit of our ability to detect EM radiation is not neccearily the edge of the universe. A bit like standing on the shore and declaring the horizon is the end of the Earth.

Becasue we don't see it doesn't mean nothing is there.

I'll have to serach for a refernce, I believe I read atoms are changing.

We may not know what the universe will do. We do have a good idea how long before the sun begins to expand incinerating Earth.

This one really doesn't get the meaning of "infinity".
EB

 

[steve_bank]

I read a cosmology book where the author used universe for the observable and detectable and Universe for the totality whatever that may be.

Anything that exists is part of the Universe. There can not be multiple Universes.

 

[Loren Pechtel]

Light looses energy through scattering and absorption resulting in heat.

Scattering doesn't lose energy. Absorption does--but heats up whatever absorbed it. That's why all non-stellar bodies in time get heated to stellar temperatures and thus vaporize.

More likely, absorbed light is re-emitted at lower frequencies, say infrared. So, it won't be visible light and therefore no bright sky to the human eye. Only deep-fry cooking.
EB

At first it will be at lower frequencies but since the energy can't be destroyed it's going to keep warming until all the extra mass floating around has reached the temperature of a star's surface.

 

[Jokodo]

Light looses energy through scattering and absorption resulting in heat.

Scattering doesn't lose energy. Absorption does--but heats up whatever absorbed it. That's why all non-stellar bodies in time get heated to stellar temperatures and thus vaporize.

More likely, absorbed light is re-emitted at lower frequencies, say infrared. So, it won't be visible light and therefore no bright sky to the human eye. Only deep-fry cooking.
EB

Only so long. Once previously none-emitting matter is heated up to the temperature of the surrounding stars, it while shine as bright as they do.

 

[Speakpigeon]

Every sight line still ends up on a star or something heated to stellar temperatures except (what I forgot before, as it wasn't known at the time) those that end up at the event horizon of a black hole

Oh, indeed, I forgot. If you have in infinity of stars in an infinite universe, you could still have a black sky at night if there's enough black holes to absorb the excess of light.

What happens to a black hole that absorb an infinite amount of energy? Anyone knows?
EB

 

[Speakpigeon]

More likely, absorbed light is re-emitted at lower frequencies, say infrared. So, it won't be visible light and therefore no bright sky to the human eye. Only deep-fry cooking.
EB

At first it will be at lower frequencies but since the energy can't be destroyed it's going to keep warming until all the extra mass floating around has reached the temperature of a star's surface.

Sure but it's not true that "all non-stellar bodies in time get heated to stellar temperatures and thus vaporize" as you said. I would only become true in an infinite universe, or at least that's what the paradox suggests.
EB

- - - Updated - - -

More likely, absorbed light is re-emitted at lower frequencies, say infrared. So, it won't be visible light and therefore no bright sky to the human eye. Only deep-fry cooking.
EB

Only so long. Once previously none-emitting matter is heated up to the temperature of the surrounding stars, it while shine as bright as they do.

Of course. See my response to LP.
EB

 

[Speakpigeon]

I read a cosmology book where the author used universe for the observable and detectable and Universe for the totality whatever that may be.

Anything that exists is part of the Universe. There can not be multiple Universes.

These people should go back to school and re-learn their English... There's already a word for "anything that exists". It's "reality".

reality
3. The totality of all things possessing actuality, existence, or essence.

EB

 

[Jokodo]

Sure but it's not true that "all non-stellar bodies in time get heated to stellar temperatures and thus vaporize" as you said. I would only become true in an infinite universe, or at least that's what the paradox suggests.
EB

But that's the whole point: to show that an infinitely old and infinitely vast universe leads to contradictions.

 

[Jokodo]

I presume you meant to say r^2. What you're missing is that the number of stars in such a shell goes up at r^2 also.

That would be dependent of the actual density of stars in this infinite universe

Very broadly, yes, but actually any non-zero average density leads to the paradox.

and more generally whether all lines of sight would be occupied by stars,

All lines of sights being occupied by stars is a consequence, not a premise.

or whether all those stars would emit at least some energy, etc. The universe could be infinite either without an infinity of stars, or with an infinity of stars spread around in a way that wouldn't light up all the sky at night

How would that work?

or with an infinity of stars but only a finite number of them emitting some energy. There could be also situations where the topology of the universe would keep the light from spreading to the whole universe. Also, the universe could be infinite but with a beginning, in which case you would only see the stars that are close enough to us consistent with our sky at night.

Indeed, but then no-one is disputing that the universe can be infinite in space. What the paradox demonstrates is that it cannot be static and infinite in space. And those who object to the Standard Model because they feel it comes too close to a universe more or less popping into existence out of nothing 13 billion years ago surely wouldn't be happy to replace it with a universe literally popping into existence as is 14 billion years ago.

Also, if you have an infinite universe that keep expanding, the light coming from distant stars won't ever reach us. Same result, our sky at night.

Sure, but in an expanding universe, going back in time eventually brings you to a point where it was, for all intents and purposes, infinitely dense. This is true whether it's expanding logarithmically, linearly, or exponentially.
And that just is the standard model. The standard model does not preclude the possibility that it's infinite in space (if anything, most cosmologists seem to prefer this possibility). What it precludes is a universe that's borderless and static.


* "borderless" is a better terminology than "infinite". If space bends in on itself so we have a finite yet borderless universe (think: the 3-d version of a sphere's surface), the paradox still arises.

 

[Jokodo]

I worked on radar, electronic countermeasures, and IR systems. One of the first thing I did was verify for myself 1/r^2.

I have done open range testing of antennas. Computing energy at a distance from a source by 1.r^2 is common.

It is not simple line of sight. In radiometry a distant star and the Earth form a frustum with finite areas of the star and Earth at the ends. As an approximation a distant star light years away looks like an isotropic source. It is a theoretical point source radiating equally in all directs over 2PI steradians.

A star is not a point source. E. g. Alpha Centauri A has an apparent radius as seen from Earth of 0.007 archseconds.

 

[Speakpigeon]

Sure but it's not true that "all non-stellar bodies in time get heated to stellar temperatures and thus vaporize" as you said. I would only become true in an infinite universe, or at least that's what the paradox suggests.
EB

But that's the whole point: to show that an infinitely old and infinitely vast universe leads to contradictions.

Sure and I wasn't addressing that. You should try to read my post in the context of LP's claim I was responding to.
EB

 

[steve_bank]

I worked on radar, electronic countermeasures, and IR systems. One of the first thing I did was verify for myself 1/r^2.

I have done open range testing of antennas. Computing energy at a distance from a source by 1.r^2 is common.

It is not simple line of sight. In radiometry a distant star and the Earth form a frustum with finite areas of the star and Earth at the ends. As an approximation a distant star light years away looks like an isotropic source. It is a theoretical point source radiating equally in all directs over 2PI steradians.

A star is not a point source. E. g. Alpha Centauri A has an apparent radius as seen from Earth of 0.007 archseconds.

You do not seem to have any understanding of applied electromagnetics and how different models are used. Computaionaly a distant star is for all practical purposes is trade like a pont source.

Can you derive inverse square without looking it up?

 

[steve_bank]

There is a simple way to address the paradox.

Generate a random distribution of stars in 3d. Then calculate the total energy at Earth. It is easy to create random vectors in tools like Scilab, free, or Matlab and Mathematica.

Compare to the threshold energy of the eye.

You can vary the density and distribution nd the mea Place stars beyond our limit of observation to see if stars way off in the distance have any meaningful impact on the results.

Numbers talk.

 

[Speakpigeon]

Very broadly, yes, but actually any non-zero average density leads to the paradox.

and more generally whether all lines of sight would be occupied by stars,

All lines of sights being occupied by stars is a consequence, not a premise.

You must be assuming a broadly random distribution of stars. Maybe not so. Suppose all stars, the whole infinity of them is lined up along one straight line. I have to guess that we would have mostly infrared radiation all coming from two opposite directions. Black sky and deep-fry cooking? Or any situation in between. So, a paradox but not that of the bright sky at night.

or whether all those stars would emit at least some energy, etc. The universe could be infinite either without an infinity of stars, or with an infinity of stars spread around in a way that wouldn't light up all the sky at night

How would that work?

You may have an infinity of stars but only a finite number of them emitting energy, although in this case you may not want to call all of them "stars". And I don't know of it's at all possible for any body to emit no energy at all, except black holes and even them in a way they do (Dawkin's something).

So, broadly, for all those, I concede the point.

or with an infinity of stars but only a finite number of them emitting some energy. There could be also situations where the topology of the universe would keep the light from spreading to the whole universe. Also, the universe could be infinite but with a beginning, in which case you would only see the stars that are close enough to us consistent with our sky at night.

Indeed, but then no-one is disputing that the universe can be infinite in space. What the paradox demonstrates is that it cannot be static and infinite in space.

If by static you mean "no beginning" then I agree, at least for that point. If by static you mean currently static, with or without a beginning, then I disagree. The point is whether there's a beginning or not.

So, I'll assume your "static" implies "no beginning" and I'll agree with that.

And those who object to the Standard Model because they feel it comes too close to a universe more or less popping into existence out of nothing 13 billion years ago surely wouldn't be happy to replace it with a universe literally popping into existence as is 14 billion years ago.

Sorry, that's all lost on me.

Also, if you have an infinite universe that keep expanding, the light coming from distant stars won't ever reach us. Same result, our sky at night.

Sure, but in an expanding universe, going back in time eventually brings you to a point where it was, for all intents and purposes, infinitely dense. This is true whether it's expanding logarithmically, linearly, or exponentially.

I can conceive of a universe that's static, without a beginning, expanding at a constant rate and in a uniforme way throughout, with an infinity of stars, that would look locally as it does to us.

Going back in time doesn't make any difference with this one.

Maybe it's against the implicit rule of the "Standard Model" but in this case the paradox is that of the standard Model, not that of an infinite universe with an infinity of stars.

And that just is the standard model. The standard model does not preclude the possibility that it's infinite in space (if anything, most cosmologists seem to prefer this possibility). What it precludes is a universe that's borderless and static.

* "borderless" is a better terminology than "infinite". If space bends in on itself so we have a finite yet borderless universe (think: the 3-d version of a sphere's surface), the paradox still arises.

If "static" also exclude expansion then I agree.
EB

 

[Speakpigeon]

There is a simple way to address the paradox.

Generate a random distribution of stars in 3d. Then calculate the total energy at Earth. It is easy to create random vectors in tools like Scilab, free, or Matlab and Mathematica.

Compare to the threshold energy of the eye.

You can vary the density and distribution nd the mea Place stars beyond our limit of observation to see if stars way off in the distance have any meaningful impact on the results.

Numbers talk.

Numbers without logic don't.
EB

 

[Loren Pechtel]

Sure but it's not true that "all non-stellar bodies in time get heated to stellar temperatures and thus vaporize" as you said. I would only become true in an infinite universe, or at least that's what the paradox suggests.
EB

The context was an infinite universe.

 

[Loren Pechtel]

I worked on radar, electronic countermeasures, and IR systems. One of the first thing I did was verify for myself 1/r^2.

I have done open range testing of antennas. Computing energy at a distance from a source by 1.r^2 is common.

It is not simple line of sight. In radiometry a distant star and the Earth form a frustum with finite areas of the star and Earth at the ends. As an approximation a distant star light years away looks like an isotropic source. It is a theoretical point source radiating equally in all directs over 2PI steradians.

A star is not a point source. E. g. Alpha Centauri A has an apparent radius as seen from Earth of 0.007 archseconds.

You do not seem to have any understanding of applied electromagnetics and how different models are used. Computaionaly a distant star is for all practical purposes is trade like a pont source.

Can you derive inverse square without looking it up?

Note the radius he specified--.007 arcseconds--thus a diameter of .014 arcseconds. The biggest optical telescope in the world, observing in blue light, has a maximum resolution of .011 arcseconds. In other words, basically one pixel. It's a point source to our best observation but that doesn't make it a true point source.