Spontaneous Energy Loss in Light

In summary: What drag said was that the light of the CMBR has lost a thousand times its original energy, as spacetime expanded.The light is still there, it is still light, but it has lost energy.The light of the CMBR has lost a thousand times its energy because of the expansion of the universe.That is something light can do: lose energy.So we know that light can lose energy.But what was your question there, Anil?You said[[So in reality a photons cannot loose all of it's energy?]]You were asking whether light can lose all its energy. Am I
  • #36


Originally posted by Alexander
Markus, please apologise for associating this idea with me.

As you can clearly see from my post about "tired light" it was to show you that YOUR idea of "stretched photons" is wrong (as you said - totally wacko).

So, apologise for putting words I did NOT say in my mouth, ok? And don't do that again. PF is not the right place for personal attacks.

I rarely read your posts but my impression is that whenever I do I am likely to find an error. If I remember correctly:

1. you invoked a global energy conservation law in Gen.Rel. and there is no such law.

2. you claimed the energy lost from CMB went into gravitational energy!

3. you claimed there could be no voltage difference between the wingtips of a plane flying thru vertical magnetic field

4. I believe you also made false assertions about the Hubble law and limitations of recession speed in GR, but I would have to look back to check.

In every thread I can remember where I've had occasion to read your posts, you have made errors and when you are wrong you tend keep adamantly reasserting the false claim.

My views are standard mainstream views. The cosmological redshift is not Doppler. Maybe in Russia or wherever you are words are used differently and it is called "Doppler" and that means something else. But the simplest explanation is that you are just eccentric and opinionated.

I am glad to hear you disavow the "tired light" notion!

Tell me your interpretation of the Hubble law v = H0 D.
In what metric is the distance D measured? At what moment in time? The speed v is the change in what measure of distance?
At what time is the v considered to be measured?

This would be a good test of whether your understanding of what these things mean is an eccentric abberation on your part.
 
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  • #37
Originally posted by LW Sleeth
I read Linder's FAQs . . . in it he brought up something I have been curious about. He says:

"What is meant by the edge of the universe where velocities reach the speed of light? There are a number of concepts put together in this question. By edge of the universe cosmologists mean the edge of the observable universe or the horizon. Just like on Earth the fact that you cannot see past the horizon doesn't mean there's nothing past there! (See the next question for more details.) This edge is equivalent to the distance light can travel in a time equal to the age of the universe."

Although he says what the edge means, he doesn't say what constitutes the edge. In other words, is the edge [of the universe] considered the the furthest reaches of matter (i.e., stars, nebula, etc.)? Or does it refer to how far light might have traveled beyond the matter it radiated from? If the edge is determined by the expansion of matter, could it be that any of it reaches the velocity of light? Finally, if it is light, then is light creating space? Or is space seen as expanding ahead of or with matter and/or light?


Anyone care to answer?
 
  • #38
The visible edge of universe is just an expression. It has no physical "edge" meaning. Universe is same here, there (near "vision edge") and beyond the edge.

Main cosmological principle is Copernicus principle: our location in space is no special than any other. By other words, universe is spatially symmetric. This imposes severe limitations on mathematically possible "designs" of universe (cosmological models). Say, that positively curved universe shall not have boundaries, but nevertheless shall have finite volume and finite size. Negative or zero curved universe shall be infinite in size and in volume.

So, we live right at the edge of universe for observer(s) 13 billion light years away.
 
  • #39
Originally posted by LW Sleeth
Anyone care to answer?

Sleeth I read Linder's FAQ and was shocked.
I like his Cosmology overview very much and admire him
both as a writer and researcher.
His Introduction to Cosmology may be a good textbook too, I haven't looked.

The FAQ was to an unmathematical lay audience and talked down a lot. Some of what he said, presumably in order to be understood, he simply should not have said.

There is a split between how cosmologists talk among themselves and what you get in popular accounts.
Within the community and with students they use the RW metric also called the FRW metric and a rest frame defined by the Cosmic Microwave Background.

Distance is often expressed as a redshift, and there is a standard way to convert this to a "comoving" distance----essentially applying the metric to give a current distance to the object.

They typically don't use "light travel time" because it is not a workable spatial distance---applies to a mishmash of different epochs.

In the FAQ he was using light travel time distance because, I guess, most general audience listeners understand distance that way.

Linder's overview was great but I would just disregard his popular-audience FAQ. I'll try to elaborate on this later.

Here's a url for Linder's good overview and for Wright's online calculator which you can use in conjunction with Linder's overview:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

hmmm I've mislaid the Linder URL have to go hunt it

Here it is

http://panisse.lbl.gov/~evlinder/lcos.pdf
 
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  • #40
I see that Alexander has just replied. He illustrates the
common misconception that the "cosmological horizon" is
currently 13 billion LY away.

that is talking in terms of light travel time.

In fact the current distance to the farthest objects we could possibly see is now 40 billion LY, in principle.
This is measured by observers at rest with respect to background, in the present, using the standard metric.

The most distant quasar that has actually been observed
is 28 billion LY away, at the present time.

the light from this quasar (observed in 2002 at redshift 6.4)
took 13 billion years to get to us----traveling through regions which were in various stages of expansion when the light came thru. And during that 13 billion years----the distance to the quasar expanded out to 28 billion LY.

Its current speed of recession is 2c. The speed of recession is the rate of change in the comoving distance---which is what plugs into the Hubble law.

Wrights tutorial is the most accessible source on this
Linder glosses over too much
 
  • #41
It is actually pretty simple and also at the same time interesting.

Toss out Linder's FAQ and look at something real, like that quasar---Wright discusses it and provides some links which I can get if you want them.

The z = 6.4 tells the story.
You plug that into a calculator (Wright has on online) using
the current value of Hubble parameter and other standard assumptions which are inputs to the metric. And it gives you 28 billion LY as the distance.

That is the distance to the thing NOW

If you want to know the distance to it when the light was emitted you just divide by 6.4.

Because space has expanded that much since the light was emitted. 28/6.4 is 4.4
So the quasar was 4.4 billion LY away when the light left it.

The light took 13 billion years to come.
But the distance THEN was 4.4 and the distance NOW is 28 billion LY.

The 13 billion year travel time is not too useful because it doesn't immediately give a good idea of the distance either then or now.

Anyway, we can't see quasars which are currently 40 billion LY away. So far we have only seen one 28 billion LY away. But IN PRINCIPLE the distance to the horizon is 40 corresponding to infinite redshift.

The CMB is at redshift 1100. You can try that in the online calculator and it will, I guess, give pretty near 40, but not quite.
Because the CMB comes from a while after the big bang, so it is not quite at the horizon.

Hope you come back with more questions and are not boggled.
It is terrible when cosmologists use light travel time distance in talking down to people. Leaves a residue of confusion in how the public thinks.
 
  • #42
Someone may have already answered me and I do not realize it, but I still haven't quite understood what is being relied on as the "edge." Is it matter only, or light?

But maybe I don't understand how light travels in our universe. If, say, the universe is considered flat and so its matter is spread out spherically, is light traveling just around that sphere, and not outwardly perpendicular to the sphere? It seems like the measurement of the universe is of distant objects like the quasar, but I then wonder if the light it emits isn't traveling beyond it "outwardly perpendicular" to the direction of expansion, and if so then should that be considered part of the size of the universe.

The other related question I have is about how fast matter is traveling in expansion. I thought I read that some galaxies are receeding at nearly the speed of light. Can matter so massive really go that fast? And are we ourselves moving as quickly away from other galaxies?
 
  • #43
the current model is that space is flat, infinite, and expanding
(which means spacetime is not flat, but that is another issue)

There is a spherical volume in space called the observable universe (radius about 40 billion LY) which contains the objects which we can in principle observe

their light has reached us, of course we can only see them
as they were in the past when the light was emitted but
those are the object we know about and can observe

they are contained in a ball currently 40 billion LY in radius.

The surface or boundary of that ball is like a horizon

Maybe you could say it is an "edge" the way our ordinary
horizon on Earth is an edge. OK word, but maybe not the best word.

Does this help?

Originally posted by LW Sleeth
Someone may have already answered me and I do not realize it, but I still haven't quite understood what is being relied on as the "edge." Is it matter only, or light?

But maybe I don't understand how light travels in our universe. If, say, the universe is considered flat and so its matter is spread out spherically, is light traveling just around that sphere, and not outwardly perpendicular to the sphere? It seems like the measurement of the universe is of distant objects like the quasar, but I then wonder if the light it emits isn't traveling beyond it "outwardly perpendicular" to the direction of expansion, and if so then should that be considered part of the size of the universe.

The other related question I have is about how fast matter is traveling in expansion. I thought I read that some galaxies are receeding at nearly the speed of light. Can matter so massive really go that fast? And are we ourselves moving as quickly away from other galaxies?
 
  • #44
Originally posted by marcus
The surface or boundary of that ball is like a horizon

Does this help?

Yes, it is mostly what I thought.

Here's what is still unanswered for me:

1. Light diverges. So does radiation travel outward and away from the horizon (essentially increasing the circumference of the horizon)? If so, is that light considered the horizen, or is it only the furtherest expanded matter that determines the horizen?

2. I'll just repeat my other question, "The other related question I have is about how fast matter is traveling in expansion. I thought I read that some galaxies are receeding at nearly the speed of light. Can matter so massive really go that fast? And are we ourselves moving as quickly away from other galaxies?"

Thanks for your patience.
 
  • #45
Whoah! I see the problem! No, space is not like the surface of a balloon!

When people say space is flat they mean like ordinary 3D Euclidean space where the sum of the angles in a triange is 180 degrees. It is the infinite 3D space we are used to. this is on a large scale. Overlooking local bumps caused by stars and black holes and stuff. There are minor local abberations from flatness but in the large it is just our usual 3D infinite space.

The difference is that it is expanding. So when you put time into the picture it is more complicated. But anyway as far as space, at anyone instant of time, goes----think of standard 3D coordinates going to infinity.

Inside this Euclidean 3D space there is a finite ball-shaped volume containing all the stuff that has been seen with telescopes so far. This ball gets larger as time goes on and more news comes in and light from farther away and longer ago arrives.

Recession speeds in cosmology are routinely faster than light.
This doesn't mean spaceships can go faster than light it just
has to be because you have an infinite thing expanding uniformly. If you look far enough out you are going to see stuff receeding
faster than light.

The Special Relativity coordinates don't apply on large scale
and the speed limit you get in SR does not apply either.
The recession speed is not like an ordinary SR speed
(could not be used for sending information or for rocket travel, is not local but is only a change in distance between widely separated points in space).

Have to go, can't finish the discussion but will get back later

Originally posted by LW Sleeth
Someone may have already answered me and I do not realize it, but I still haven't quite understood what is being relied on as the "edge." Is it matter only, or light?

But maybe I don't understand how light travels in our universe. If, say, the universe is considered flat and so its matter is spread out spherically, is light traveling just around that sphere, and not outwardly perpendicular to the sphere? It seems like the measurement of the universe is of distant objects like the quasar, but I then wonder if the light it emits isn't traveling beyond it "outwardly perpendicular" to the direction of expansion, and if so then should that be considered part of the size of the universe.

The other related question I have is about how fast matter is traveling in expansion. I thought I read that some galaxies are receeding at nearly the speed of light. Can matter so massive really go that fast? And are we ourselves moving as quickly away from other galaxies?
 
  • #46
Originally posted by LW Sleeth


2. I'll just repeat my other question, "The other related question I have is about how fast matter is traveling in expansion. I thought I read that some galaxies are receeding at nearly the speed of light. Can matter so massive really go that fast? And are we ourselves moving as quickly away from other galaxies?"

Thanks for your patience.

Thx enormously for YOUR patience, not always easy for me to say things concisely.

YES we are going away from the other galaxies at speeds near and even exceeding the speed of light. The uniform expansion of infinite space requires this. If there are conscious beings in other galaxies they would think of us as receding. But it is not like rocketship travel---it is just space spreading out. No one is going anywhere, is some sense. Just separation increasing in some cases at 2c in some cases 3c and so on----all different speeds depending on how far away.



Originally posted by LW Sleeth
Yes, it is mostly what I thought.

Here's what is still unanswered for me:

1. Light diverges. So does radiation travel outward and away from the horizon (essentially increasing the circumference of the horizon)? If so, is that light considered the horizen, or is it only the furtherest expanded matter that determines the horizen?


Have to postpone answer, busy. Be back
 
  • #47
Originally posted by LW Sleeth
Yes, it is mostly what I thought.

Here's what is still unanswered for me:

1. Light diverges. So does radiation travel outward and away from the horizon (essentially increasing the circumference of the horizon)? If so, is that light considered the horizen, or is it only the furtherest expanded matter that determines the horizen?


Good thinking. It works both ways
this spherical volume containing things we have seen also
can be thought of as the ball of space which our light has reached
or which light from our location could have reached if something here had been making light from the beginning.

Ned Wright, in one example, looks at it that way.

He is explaining why the radius of the observable universe is about 40 billion LY and why the boundary is receding at speed around 3c. I will try to find the page reference and give a link.

So it is the spherical volume containing things whose light has reached us and ALSO reciprocally the volume of where our light (if we had making it from the very start) would have reached.

Our galaxy didnt get started glowing exactly at the beginning, so its actual light hasnt quite reached that far, but that is the rough idea. It works both ways.
 
  • #48
Yeah, here it is
http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN

It is from Wright's Cosmology FAQ and is called

"If the Universe is only 10 billion years old, how can we see objects that are now 30 billion light years away?"

For easy numbers he is considering a Einstein de Sitter universe
(no extras) that is 10 billion years old

So he has the radius be 30 billion LY

Just as with a more realistic model with age something over 13 billion years
the radius is around 40 billion LY

He considers a galaxy out near the horizon and also
a photon of light passing that galaxy and heading outwards.
It could have been one emitted by us, if we had had a light on at the beginning.

He does a little arithmetic to let time pass a bit and then looks
at it again and the boundary has moved out and the photon is
right there keeping pace with it.

I think what you concluded intuitively is right and this calculation, tho simplified for easy numbers, confirms your intuition.
 
  • #49
Originally posted by marcus
Good thinking. It works both ways
this spherical volume containing things we have seen also
can be thought of as the ball of space which our light has reached or which light from our location could have reached if something here had been making light from the beginning.

Thank you for clearing that up. The reason I wondered is related to an additional question I've been pondering which is, what is creating "space"?

Some have said that the expansion of the universe creates space as it goes along; that before the space of our universe gets there, there is nothing at all. Our space seems not a void after all with virtual particles popping in and out, dark matter, and the possibility of a cosmological constant (and the theoretical Higgs field?). In other words, while space may be the absence of matter, it also may be dynamic in certain respects.

So, I wondered if as the universe expands, what exactly defines the creation of new space on the horizon. Is it the light traveling ahead of matter expansion creating it? Or could possibly the qualities of space itself be expanding just ahead of light and everything else, creating the potential for the rest to follow?

(Getting that headache yet? :smile: )
 
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  • #50
Hello Sleeth thanks for the new question, more to think about. But there was still a bit of grist for my mill in what you said earlier


Originally posted by LW Sleeth The other related question I have is about how fast matter is traveling in expansion. I thought I read that some galaxies are receeding at nearly the speed of light. Can matter so massive really go that fast?
[/B]

this is the most important question because it involves RECONCILING the local SR picture with the global GR picture.

It is easy for distant galaxies to be receding at twice the speed of light or more and it does not make them more massive. It is inevitable that some galaxies would be doing this because of the uniform expansion of space. Yet this does not contradict Special Relativity, which is about relative speeds of things at the same point in space or in the same locale.

The coordinates of SR are called "Minkowski" and Minkowski coordinates don't apply in the large. The Minkowski spacetime
of Special Relativity has no ability to expand. In the real universe you can only apply Minkowski coordinates in a small local region,
like a bandaid. There is no bandaid that covers the whole person.

No rocket ship could PASS THE EARTH going over the speed of light. Indeed in our local coordinates as things approach the speed of light their energy (measured in our local laboratory coordinates) grows unboundedly. They become harder and harder to speed up any further---taking more and more energy to get the next little bit of speed.

But that is no reason why a distant galaxy can't be just sitting still in the space around it and receding from us at twice the speed of light. Thousands of galaxies are doing just that. It does not contradict SR because it is not in our laboratory, or in the sun's neighborhood, or in our local Minkowski coordinates----however you want to say it.

We did not invest energy to accelerate those distant galaxies. They don't have any extra energy or mass just because they are sailing away at twice the speed of light. They have to, because space is expanding, and they are not in the same local SR Minkowski coordinte frame with us.

The distance to them is measured with a METRIC, the robertson walker metric which is able to deal with spacetime curvature and cope with expansion and do stuff which the rigid Special Relativity metric ("minkowski metric") cannot do.

So...different idea of distance...leading to different idea of speed...NO PROBLEMO! Galaxies receding at twice the speed of light and yet no weirdness like tachyons and going backwards in time and killing your grandfather and circus freak infinite energy stuff. All those things are stories told in a Special Relativity surround.

They recede at twice the speed of light and more because they are outside the purvue and jurisdiction of Special Relativity and there is no weirdness.


Originally posted by LW Sleeth
Thank you for clearing that up. The reason I wondered is related to an additional question I've been pondering which is, what is creating "space"?

Now this is a REALLY interesting question. I will think a bit before answering. I think you would be satisfied if we just kept the DENSITY of mysteries like dark energy constant and space expanded.

If there is always the same amount of virtual X-particles PER CUBIC METER, then if your one cubic meter volume expands to be two cubic meters you now have twice as many virtual X-particles or "weirdons" or whatever. And twice as much of all the other familiar inhabitants of the vacuum as well.

That should be enough goodies for anybody. Let's not talk about space as if it were a commodity. If it expands and the per-volume quantity of all this mysterious stuff stays the same, then we get more goodies. the mystery remains, but phrased more acceptably IMHO.

It is definitely mysterious. 73 percent of the energy in the U is called "dark energy" and nobody has a convincing theory of what it is and it has never been detected. And the assumption is that the density of it is constant over space and time. So what makes more---to keep the density constant when space expands? [?]

It is one of the questions that make life worth living. I mean it.
 
  • #51
Originally posted by marcus
Galaxies receding at twice the speed of light and yet no weirdness like tachyons and going backwards in time and killing your grandfather and circus freak infinite energy stuff. All those things are stories told in a Special Relativity surround. . . .

Now this is a REALLY interesting question. . . . It is definitely mysterious. 73 percent of the energy in the U is called "dark energy" and nobody has a convincing theory of what it is and it has never been detected. And the assumption is that the density of it is constant over space and time. So what makes more---to keep the density constant when space expands? [?]

It is one of the questions that make life worth living. I mean it.

Thanks for clarifying the speed thing . . . I can see why (I think) that expanding space causing recession faster than c isn't a problem.

This thread was really my round-about way of asking about the creation of space. I'd wondered if light moving ahead of matter expansion on the horizon might be doing it; and if so, and if light were losing energy over time, then if the integrity of new "space" might suffer too. You said that the light inside our universe is stretching and losing energy as it does, but I suppose that would not necessarily apply to the light leading expansion.

Yet apparently no one understands what is creating space. You seem resistant to instilling space with qualities, yet in addition to the other properties I mentioned it is powerful enough to move galaxies apart faster than the speed of light! That is why I suspect there is more to space than most seem to want to credit it with.

For example, usually it is said that acceleration or mass produces the gravity effect. But might not gravity be a property of space? That is, when there is a concentration of energy, such as the energy concentrated to accelerate or the huge amount of energy packed into matter, then that causes space to constrict. The higher the concentration of energy, the more the constriction.

The constancy of light speed too could be due to a certain tension space maintains of which light speed reflects. I always wondered why light and atoms oscillate rhythmically. A guitar string only does so, for instance, when it is under a certain degree of tension; without that minimum tension it flops around chaotically when plucked.

Both light speed and gravity could be the result of a single type of polarized tension of space, a divergent-convergent polarity. So when something reaches the density of light, the divergent side sends it off at light speed (rhythmically oscillating from the push-pull of the polarity), and when something exhibits more than that density, the convergent side kicks in constricting in on it.

These obviously are speculations of a "why" person; you can already tell I am not properly versed in the "how." I probably better cool it before a mentor transfers this thread to theory development!

Thanks for the interesting discussion so far. I am enjoying the heck out of it.
 
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  • #52
Les, first to clear one point up that, as I understand it, marcus doesn't quite explain right. No one or nothing is creating space. Spacetime itself is expanding as marcus said but one cubic meter prior to the expansion is still one cubic meter after expansion because the meter would expand with space. The way we measure the expansion is the red shift of the light emitted by galaxies far away. As it take millions of years, even billions of years for the light to get to us, a significant amount of expansion takes place. Also the further apart we are, the faster we recede from one another. As space expands the wavelength of the light also expands changing the period of the wave, the wavelength become longer, lower in frequency and thus red shifted. Some galaxies are so far away that the light from it has shifted beyound even infared to radiowaves and can only be detected by radio telescopes.

I've thought about your last question quite a bit lately. If the universe is expanding into dimensionlss, timeless space what would happen if a photo left our sace time and went into the void? I have no way of proving this and it is only speculation on my part but if it did happen then the photon would no longer have any velocity or momentum as V and M are meaningless in such a void or nul-space as I call it. If a photon or EM wave had no velocity it could no longer be a photon or EM wave and would instantly turn into matter, probably a string which is energy vibrating in a dimensional loop.
This would of cours be creating at least one dimention and that area of the void would no longer be dimensionless and therefore be spacetime. This would be creating spacetime in the sense that I think you mean. As I said this is pure speculation on my part.
 
  • #53
Originally posted by Royce
Les, first to clear one point up that, as I understand it, marcus doesn't quite explain right. No one or nothing is creating space. Spacetime itself is expanding as marcus said but one cubic meter prior to the expansion is still one cubic meter after expansion because the meter would expand with space.
Yes, that's pretty much how I see it -- I think it has been me that's used the word "create." A better term would probably be "determine," to describe what I'm asking. To me there seems to be a bit of a contradiction in the ambiguity in the definition of space.

If space is a void, then what is it expanding into? If someone says there is nothing there, not even space, then space is clearly of a different nature from nothing -- it is "something." It can serve as the medium for matter, for instance. Where matter isn't, seems to be what is being referred to as "nothing."

I've been trying to understand what makes space different from "nothing." As the universe expands, what exactly differentiates space from the nothing it is expanding into? Matter? But then, I wondered about the light going on ahead of it, does that determine the nothing has now become "space"? Or is more required, something else that is expanding along with light, that defines/determines space?
 
  • #54
In a word, Dimensions. That is the difference between space and nothing or void or my nul-space. There are a number of people other than me who think that matter is what makes its spacetime. matter gane only exist in spacetime and if string theory is correct tthen matter in the form of strings is energy vibrating within a loop of a dimesion. Someone figured out that it would only take 28 dimensions to account for everything that exist. I think that the number is now down to 11.
One other thing about what I previously posted. It is speculated that while the universe is expanding it might still be a singularity or perhaps better a black hole. As such no photons could escape our universe and so no more space could be created.
This is about as far as I can go or the pain starts. I run into the same problem with Quantum Mechanics.
 
  • #55
Hello Royce, Sleeth,
it seems a shame to quibble about one point---I like a lot of your speculation and agree with some of the background science you point to---but one of the hardest things to understand is that even tho on the large scale space is expanding the sizes of ATOMS don't grow.

Indeed in the picture of expansion cosmologists give us----*galaxies* don't get bigger they just get farther apart.

Even local clusters of galaxies can overcome expansion and stay together if they attract each other enough. A good cohesive cluster of galaxies falls back together and overcomes expansion. So it doesn't get disassembled. But that is a grey area---for the most part galaxies drift apart (but because within themselves they are securely gravitationally bound, they stay the same size)

the basic modules of life retain their integrity even tho largescale things drift apart

In fact if you see a photo of a redshift z=2 galaxy that means space has expanded by a factor of 1+z, or 3, since the light left it. And that galaxy is to all intents and purposes just a usual-looking thing. The expansion of space hasnt made US NOW significantly different from IT THEN. Other things may be different. But it is not smaller just on acount of living in an epoch when space hadnt expanded yet by that factor of 3.

We know not to worry about expansion effecting things on a local, solar system, or even Milky Way, scale.
And meters are not effected.

So a distance of a trillion meters, after space has expanded by a factor of two, becomes 2 trillion meters.

If atoms don't change size, then you wouldn't expect metersticks to change either----the size of our units of measurement is not linked to this largescale intergalactic distance expansion process.

Not to say I or anyone really understands this expansion---but simply that's how the prevailing model looks. Sorry if it seems inconsistent that only some things expand and other things dont---I realize the unintuitive aspect here.

Must go. Hope not too much of a ramble.

(of course just because a model happens to be the prevailing one at the time doesn't mean it is the ultimate truth! but still worth reporting I think)
 
  • #56
must also add that there are people who
because of an observed speeding up of the expansion rate
have projected this acceleration hundreds of billions of
years---very far, don't remember---into the future and
come up with scenarios in which familiar entities like
galaxies are pulled apart

expansion becomes so rapid as to overcome their
integrity as gravitationally bound systems
their gravity is no longer able to fight it

and even worse, modules even smaller than galaxies are
pulled apart. I don't find these speculative scenarios interesting
or appealing

this is just a kind of linear projection taken to extremes
we don't know much about the dark energy responsible for
accelerated expansion---not enough to project how it will
be far in the future. pretty much pure speculation and not
to worry about

for the foreseeable future nothing of any consequence expands
except the largescale distances between galaxies and the wavelengths of the light traveling across those wide reaches of space. atoms and
metersticks stay the same size (paradoxically one might say)
if I have given a distorted picture perhaps someone else will
correct it.
 
  • #57
Originally posted by marcus
must also add that there are people who
because of an observed speeding up of the expansion rate
have projected this acceleration hundreds of billions of
years---very far, don't remember---into the future and
come up with scenarios in which familiar entities like
galaxies are pulled apart . . . expansion becomes so rapid as to overcome their integrity as gravitationally bound systems
their gravity is no longer able to fight it . . . we don't know much about the dark energy responsible for accelerated expansion---not enough to project how it will be far in the future. pretty much pure speculation and not to worry about

Thank you Marcus and Royce for the thoughts and information.

In some threads I've seen people discuss the possiblity that the universe will expand forever. I always felt they overlooked the fact that the universe is also coming apart. It is expanding and radiating away, losing structural integrity. And possibly after some 10^50 years when most present protons should be taking a turn for the worse, the universe may become just someplace where it all used to be.

If we could travel ahead in time and observe this place, I wonder what there would be. Trying to imagine this is partially why I asked the question of this thread (i.e., if light spontaneously loses energy). I've wondered if we might not find a vast area something similar to cosmic background radiation.

It wouldn't quite be like background radiation however because it would be a lot more "stretched out" than it is now. That is, it would have lost virtually all its energy and so have elongated so much it would be oscillating far too subtly for any equipment we currently have to detect.
 
  • #58
Yeah, Les, total entropy. I've read other speculations about it. Eventually the universe would look like the COBE background. I find that hard to imagine. Wouldn't gravity keep cold chunks of rock held in place at least locally? I sure don't know.
 
  • #59
Originally posted by Royce
Les, first to clear one point up that, as I understand it, marcus doesn't quite explain right. No one or nothing is creating space. Spacetime itself is expanding as marcus said but one cubic meter prior to the expansion is still one cubic meter after expansion because the meter would expand with space. The way we measure the expansion is the red shift of the light emitted by galaxies far away.

No, meter stick is not expanding with space because e/m interaction (atoms holding meter stick) is independent of space expansion.

By the same reason a photon does not stretch with expansion of space, Marcus is wrong here, energy of photon conserves, thus frequency and wavelength too (in vacuum). Redshift of distant galaxis is just due to fact that they are moving away from us due to space expansion (Doppler shift due to coordinate transformation).
 
  • #60
Royce, I certainly do admire your signature quote:wink:

>>As always with respect,

>>Royce

>>"If you find yourself arguing with a fool, then the chances are
>> that he is doing the same thing."
 
  • #61
Originally posted by Alexander
. . . Marcus is wrong here, energy of photon conserves, thus frequency and wavelength too (in vacuum). Redshift of distant galaxis is just due to fact that they are moving away from us due to space expansion (Doppler shift due to coordinate transformation).

Well, I wish somebody would clear this up, I am very interested in knowing. Is this a dispute that is going on among cosmologists, or is there consensus? Other opinions would be welcome.

Alexander, from my understanding of what Marcus said, it didn't seem to me that he was disputing that the reshift observed from distant galaxies is due to the Doppler effect.
 
  • #62
Originally posted by LW Sleeth
Well, I wish somebody would clear this up, I am very interested in knowing. Is this a dispute that is going on among cosmologists, or is there consensus? Other opinions would be welcome.

Alexander, from my understanding of what Marcus said, it didn't seem to me that he was disputing that the reshift observed from distant galaxies is due to the Doppler effect.

You might get into it at the level of a classic textbook like
Frank Shu
The Physical Universe: An Introduction to Astronomy
1982

He is a senior guy in the department at UC Berkeley.

Or another guy at Berkeley, Eric Linder, since he has some
notes online called Cosmology Overview. I would take his
FAQ for the layman with a grain of salt since very popularized
but his Cosmology Overview here is OK:

http://panisse.lbl.gov/~evlinder/lcos.pdf

I don't know any mainstream cosmologists who would agree with Alexander that the cosmological redshift is best viewed as a doppler shift.

Frank Shu warns strongly against interpreting (cosmological) z as a doppler shift because it is a common cause of confusion.
He draws a couple of diagrams (pages 373, 374) and goes into a couple of pages of discussion to make sure students understand.

EM wave propagation, Maxwells eqns, takes place in space and tiny changes in metric have a cumulative effect. Shu uses the
figurative way of describing it that I do---he says it is better to think of it as wavelengths being "stretched out" than to picture it due to Doppler.

Linder takes it for granted that the (cosmological) 1+ z is simply the ratio of the scale factors a(t) at emission time and reception time----nothing to do with velocity of emitter at time of emission.

the formula he presents (a non-doppler) is the one all cosmologists use that I have ever seen

1+z = a(trec)/a(tem)

a(t) is the parameter in the metric that keeps track of the expansion of space. The Hubble parameter changes with time
and is defined as the time derivative of a(t) divided by a(t).

That is, essentially the time-rate of expansion but as a fraction of current size.

da/dt divided by a

That is just how everybody defines the Hubble parameter and
the usual metric is R-W defined using a(t) and
the consensus formula for cosmological redshift (as distinct from individual motion doppler) is this ratio involving a(t) I told you.

People will say different things when they POPULARIZE but what I am saying is, I believe, very consensus mainstream cosmologists' view of cosmo redshift.

Alexander's viewpoint is highly eccentric or reflects a deep misconception. Dont understand his continual repetition of it.

Anyway he is welcome to see it as Doppler---that way is very common in newspapers and popular books because more easily understood by non-technicals.

But try to understand it as a stretching out as space expands
and eventually things will make better sense to you. Promise:wink:
 
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  • #63
Hi, I am new! so hi to everyone

I guess a photon could spontainiously lose energy, if it coincidentally collided with a virtual particle, that is created along its trejectory.

The photon would recoil and lose energy, in accord with the compton effect! But would be
deflected at some unknown agngle!

The lost energy of the photon, would have to create a new photon of a longer wavelength.
As it recoiled with the virtual particle. Before the virtual particle disappeared again!
:smile:
 
  • #64
Originally posted by marcus
But try to understand it as a stretching out as space expands
and eventually things will make better sense to you. Promise:wink:

Thanks. Actually as you explain it is exactly how I want to see it since it coincides with a little theory I have. I don't mind doing my homework but it is difficult for laypersons to find much discussion of such things in language we can understand.

I have a hypothetical for you, which I will ask in two parts. Part I: How far do you think light might "stretch." Say 10^100 years from now the matter of the universe has radiated away its energy, and so all that is left is a vast continuum of cosmic radiation. I realize according to what you've said light's energy could eternally decrease incrementally, but what if light has a base state where it blends into one huge subtle wave.

Part II: Now imagine this vast continuum reversing its direction, so that base state light begins to converge on a point until it reaches some critical degree of convergence and explodes. In other words, might not the universe be the result of light caught up in a cycle of convergence and divergence?
 
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  • #65
Originally posted by LW Sleeth


I have a hypothetical for you, which I will ask in two parts. Part I: How far do you think light might "stretch." Say 10^100 years from now the matter of the universe has radiated away its energy, and so all that is left is a vast continuum of cosmic radiation. I realize according to what you've said light's energy could eternally decrease incrementally, but what if light has a base state where it blends into one huge subtle wave.

Part II: Now imagine this vast continuum reversing its direction, so that base state light begins to converge on a point until it reaches some critical degree of convergence and explodes. In other words, might not the universe be the result of light caught up in a cycle of convergence and divergence?

I. Light that is redshifted enough becomes undectable. We both are contemplating this.
You came up with a nice image of it----the light is dissolving into the vacuum-----is reabsorbed by the universe.
But a spoilsport with a lame imagination might prefer to look at it as the light's energy just goes to zero---it fades out of existence---as it is progressively more and more redshifted.
All I can do here is what I always try to do----look at the same thing both ways: in a cold objective light and also in figurative imagery, and to refuse to choose between them.

II. I have not heard any evidence that the universe is slated to recompress itself and its light.

The sparsity of matter and the observed spatial flatness suggest boundless expansion.

But IF it were start falling back together all the stretched-out-to-almost-nothing light would start coming back to life.

The CMB which is now 2.725 kelvin was once upon time 3000 kelvin. This 2.725 kelvin is the basic temperature of space (now). If the universe were to collapse the basic temperature of space would rise to
3000 kelvin (less than the surface of the sun but more than the tungsten filament of a 100watt lightbulb) as it was in its beginning.

And that wouldn't even be the end of it----the CMB was emitted after the universe had existed 300 thousand years. So when 3000 kelvin were reached there would still be 300 thousand years left to continue collapsing. The temperature would keep on rising. Space would be like the inside of a star.

To be fully human I expect one must try to look at these things both skeptically and objectively
(there is no suggestion of anything but continued expansion) and also responsively.

You asked about "bounce" scenarios:
dark energy estimated to be 73 percent of the total energy density in the universe is the key to that possibility. there is not enough light. the light could not cause a collapse to "bounce" but dark energy (under certain assumptions) could cause a bounce----ive seen such scenarios plotted out but they are too speculative for me---cant find them interesting. Simply burning up is poetical enough:wink:
 
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  • #66
Originally posted by marcus
Simply burning up is poetical enough

Thanks Marcus, it has been interesting. :smile:
 
<h2>1. What is spontaneous energy loss in light?</h2><p>Spontaneous energy loss in light refers to the phenomenon where light particles, also known as photons, lose energy as they travel through a medium or interact with other particles. This can occur through various processes such as scattering, absorption, and emission.</p><h2>2. What causes spontaneous energy loss in light?</h2><p>The main cause of spontaneous energy loss in light is the interaction between photons and matter. When photons encounter particles in a medium, they can be absorbed or scattered, leading to a decrease in their energy. Additionally, spontaneous emission can occur when excited particles release energy in the form of photons.</p><h2>3. How does spontaneous energy loss affect the behavior of light?</h2><p>Spontaneous energy loss can alter the behavior of light in several ways. It can cause a change in the direction of light through scattering, or a decrease in its intensity through absorption. It can also lead to the emission of new photons with lower energy, resulting in a change in the wavelength of light.</p><h2>4. Is spontaneous energy loss in light always undesirable?</h2><p>No, spontaneous energy loss in light can have both positive and negative effects. In some cases, it can be harnessed for useful purposes, such as in fluorescence and laser technology. However, in other cases, it can lead to a decrease in the efficiency of light-based devices and systems.</p><h2>5. How can spontaneous energy loss in light be minimized?</h2><p>To minimize spontaneous energy loss in light, various techniques can be employed depending on the specific situation. For example, using materials with low absorption coefficients can reduce the amount of energy lost through absorption. Additionally, controlling the environment and temperature can also help minimize spontaneous energy loss. In some cases, advanced technologies such as metamaterials can also be used to manipulate the behavior of light and reduce energy loss.</p>

1. What is spontaneous energy loss in light?

Spontaneous energy loss in light refers to the phenomenon where light particles, also known as photons, lose energy as they travel through a medium or interact with other particles. This can occur through various processes such as scattering, absorption, and emission.

2. What causes spontaneous energy loss in light?

The main cause of spontaneous energy loss in light is the interaction between photons and matter. When photons encounter particles in a medium, they can be absorbed or scattered, leading to a decrease in their energy. Additionally, spontaneous emission can occur when excited particles release energy in the form of photons.

3. How does spontaneous energy loss affect the behavior of light?

Spontaneous energy loss can alter the behavior of light in several ways. It can cause a change in the direction of light through scattering, or a decrease in its intensity through absorption. It can also lead to the emission of new photons with lower energy, resulting in a change in the wavelength of light.

4. Is spontaneous energy loss in light always undesirable?

No, spontaneous energy loss in light can have both positive and negative effects. In some cases, it can be harnessed for useful purposes, such as in fluorescence and laser technology. However, in other cases, it can lead to a decrease in the efficiency of light-based devices and systems.

5. How can spontaneous energy loss in light be minimized?

To minimize spontaneous energy loss in light, various techniques can be employed depending on the specific situation. For example, using materials with low absorption coefficients can reduce the amount of energy lost through absorption. Additionally, controlling the environment and temperature can also help minimize spontaneous energy loss. In some cases, advanced technologies such as metamaterials can also be used to manipulate the behavior of light and reduce energy loss.

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