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ToSeek
2005-Feb-28, 05:20 PM
Leaking Gravity May Explain Cosmic Puzzle (http://www.space.com/scienceastronomy/dark_energy_050228.html)


Scientists may not have to go over to the dark side to explain the fate of the universe.

The theory that the accelerated expansion of the universe is caused by mysterious "dark energy" is being challenged by New York University physicist Georgi Dvali. He thinks there's just a gravity leak.

George
2005-Feb-28, 08:25 PM
What will they call it?

Probably not Modified MOND.

How about MOED (MOdified Einsteinian Dynamics) :wink:

Tacitus
2005-Feb-28, 11:04 PM
Quick, remember to point out to Jeremy that this theory calls for this gravity leakage to be measurable only over cosmic distances!

(i.e. not via space probe trajectory measurements around Saturn)

CJSF
2005-Feb-28, 11:26 PM
Quick, remember to point out to Jeremy that this theory calls for this gravity leakage to be measurable only over cosmic distances!

(i.e. not via space probe trajectory measurements around Saturn)

Did you mean Jerry?

CJSF

Bozola
2005-Feb-28, 11:47 PM
This repulsive, unknown force is believed to make up more than 70 percent of the mass-energy budget of the universe.


I always found it hard to believe that there could be so many estate agents...but it would have answer so many questions.

Normandy6644
2005-Mar-01, 12:38 AM
Quick, remember to point out to Jeremy that this theory calls for this gravity leakage to be measurable only over cosmic distances!

(i.e. not via space probe trajectory measurements around Saturn)

Did you mean Jerry?

CJSF

Well maybe some random guy named Jeremy was concerned about the scale of the theory, but now it's all cleared up for him!

Tacitus
2005-Mar-01, 01:56 AM
Quick, remember to point out to Jeremy that this theory calls for this gravity leakage to be measurable only over cosmic distances!

(i.e. not via space probe trajectory measurements around Saturn)

Did you mean Jerry?

CJSF

Well maybe some random guy named Jeremy was concerned about the scale of the theory, but now it's all cleared up for him!

LOL!

Yes, I meant Jerry (though I'm sure Jeremy will be happy to know that too).

crosscountry
2005-Mar-01, 03:01 PM
who here actually believes that Gravitons transmit the gravitional information.



hard for me to figure. virtual photons transmit EM information. hard to figure too.

Tacitus
2005-Mar-02, 06:31 AM
who here actually believes that Gravitons transmit the gravitional information. hard for me to figure.

It's a working hypothesis that many physicists think fits the data. Further theoretical and practical studies will prove or disprove it, but you have to start somewhere.

Is it any stranger than the idea that light behaves both like a wave and a particle depending on how you measure it?

I'm curious, why is it hard for you to figure? Is it just a feeling, or do you have more concrete arguments?

crosscountry
2005-Mar-02, 04:19 PM
I think you mean "SOME" physicists.

I think it is more strange than light's dual behavior. There are particles that are virtual yet carry information???

doesn't that lead to an infinite energy??? where do these virtual photons come from? when the leave the charge why doesn't the charge lose energy? when the sun emits a EM radiation, it loses energy.

REMEMBER the conservation of energy?

infinite energy is my problem with graviton and virtual photons.


I prefer the warped space idea of Einstein. the idea of Potential also works for me.

CJSF
2005-Mar-02, 04:23 PM
I prefer the warped space idea of Einstein. the idea of Potential also works for me.

Yes, but what's causing space to warp and how? What does it mean to "warp space?" The graviton provides a way of describing that. There are other ideas, to be sure, but what framework do they fit in?

CJSF

Grey
2005-Mar-02, 05:53 PM
I think you mean "SOME" physicists.
I'd say "most" physicists.


I think it is more strange than light's dual behavior. There are particles that are virtual yet carry information???
Well, the information has to be transferred somehow. Prior to a quantum treatment with virtual particles, the assumption was that a field carried that information, but to be fair, a "field" is just about as elusive as a virtual particle is.


doesn't that lead to an infinite energy??? where do these virtual photons come from? when the leave the charge why doesn't the charge lose energy? when the sun emits a EM radiation, it loses energy.

REMEMBER the conservation of energy?

infinite energy is my problem with graviton and virtual photons.

We were just talking about this on the thread you started to ask this question, remember? Virtual particles are not a source of constant energy drain on a system.

crosscountry
2005-Mar-02, 06:53 PM
We were just talking about this on the thread you started to ask this question, remember? Virtual particles are not a source of constant energy drain on a system.

right, but from where do the come? they are only virtual because they contain no momentum or energy? how do they transmit information without transmitting energy or momentum? Something has to do that.

so, gravitons are like virtual photons? thus, they are not detectible. thus not proveable? do i read that right?






I prefer the warped space idea of Einstein. the idea of Potential also works for me.

Yes, but what's causing space to warp and how? What does it mean to "warp space?" The graviton provides a way of describing that. There are other ideas, to be sure, but what framework do they fit in?

CJSF

I'm not sure how to describe the warpage of space anymore than what you're talking about.

here's a wrench for you; light passes a nearby galaxy. it is "lensed" as described by Einstein. if gravitons (small particles) were the culprit only some of the light would be bent; the light photons "hit" by the gravitons. the light not "hit" by the gravitons would not be effected, and thus not bent.

To me that is an incosistency in the graviton theory. Unless someone can explain it better to me. ---- How can gravitons effect light in the form of gravitational lensing?

crosscountry
2005-Mar-02, 06:56 PM
I'm curious, why is it hard for you to figure? Is it just a feeling, or do you have more concrete arguments?


I'm still working on that.

Thanks everyone for the discussion.
=D>

I hope that I don't sound rude. :oops:

Grey
2005-Mar-02, 08:31 PM
right, but from where do the come?
Well, they appear out of vacuum. :) I realize that's probably not all that satisfying, but the more we look at things at the smallest scale, the more it looks as though vacuum isn't empty space, but rather a roiling mass of virtual particles popping in and out of existence. Why is that necessarily worce than suggesting that there's some mysterious "potential" or "field" that "just exists", or that the fabric of spacetime, whatever that is, can be warped. All the models that we use tend to posit the existence of some pretty mysterious aspects of the universe.


they are only virtual because they contain no momentum or energy? how do they transmit information without transmitting energy or momentum? Something has to do that.
No, they're virtual because they can appear "from nowhere". They can carry energy and momentum (either positive or negative) between particles, which is exactly the way particles exchange energy and momentum when they interact by some force. The nature of the forces we observe can be determined from the nature of the interactions. For example, the inverse square law of gravity and electromagnetism follows naturally from this model. The much shorter ranges of the strong and weak nuclear forces arises from the fact that their carrier particles have mass, and so cannot travel as far before the energy they "borrowed" has to be paid back. I realize that I'm speaking in generalities, but the real reason for considering this a viable model is that the results work out in beautiful agreement with experiment.


so, gravitons are like virtual photons?
Virtual gravitons are like virtual photons, carriers of the gravitational force. Real gravitons would be gravitational radiation, just like real photons are electromagnetic radiation. It's just that since gravity is so much weaker, gravitational radiation is much, much harder to detect.


thus, they are not detectible.
The virtual ones are not directly detectable. Real gravitons would be, although we get to the particle/wave nature of things. You'd also want to show that there was a particle-like aspect to them (that is, that a purely wave model wouldn't explain the observations), which is probably trickier than detecting the gravitational radiation in the first place. How do you set up the gravitational equivalent of the photoelectric effect? :)


thus not proveable?
Depends on what you mean by "proveable". No, really. :D We can't directly see any of the subatomic particles we believe exist, we have to infer their existence from interactions. But I think we're all pretty confident that quarks, electrons, photons, and so forth really exist, even if they sometimes have surprising properties. In science, nothing is ever really "proven", but we do have theories in which we have a great deal of confidence.

So what about virtual particles? Remember I mentioned that once they were proposed, particle physicists realized that if there really are clouds of virtual particles around, that should have some measurable effects in things like the magnetic moment of the electron, or the energy levels in atoms. So experimenters checked, and in fact the experiments agree with the predictions that include virtual particles, and disagree with those that do not. I'd consider that strong experimental support.


here's a wrench for you; light passes a nearby galaxy. it is "lensed" as described by Einstein. if gravitons (small particles) were the culprit only some of the light would be bent; the light photons "hit" by the gravitons. the light not "hit" by the gravitons would not be effected, and thus not bent.

To me that is an incosistency in the graviton theory. Unless someone can explain it better to me. ---- How can gravitons effect light in the form of gravitational lensing?
In principle, every two particles anywhere are linked by interacting virtual particles, so we have every single photon interacting with every single particle in the galaxy. And this goes in both directions. Not only are virtual gravitons "emitted" by a random electron, but the passing photon sends out its own virtual gravitons.

So, the way you'd work out the effect would not be to look at some spread of virtual gravitons and figure out the scattering cross section of the passing photons and work out the collision results. Instead, you'd look at the passing photon and each particle in the lensing galaxy. Technically, there are infinitely many interactions that you have to take into account to work out how any two particles will react to each other. This was actually a problem with the early development of the theory, since it looked like you'd always get an infinite result. But it turns out that the more complex the interaction, the less likely it is (more or less), and so it doesn't affect things as much. You can go down as many levels as you need to in order to get results as accurate as you'd like, in principle at least. Then you'd need to look at the next particle in the lensing galaxy and determine its effect, and so on.

That sounds like a heck of a lot of work! And it would be, actually. But just like we approximate relativity and use Newton's mechanics when we can, in order to make the calculations easier, we use approximations of the quantum model when we can. And we can work out corrections from quantum theory and apply them to the classical picture when the results would be nearly classical, but not quite. And again, the agreement with experiment is amazing.

If you want a better discussion of how this interaction model works, take a look here (http://www2.slac.stanford.edu/vvc/theory/feynman.html), for example, to learn a bit more about how the theory applies to electromagnetic interactions. You can find more in-depth discussions with a simple Google search.

Brady Yoon
2005-Mar-03, 01:10 AM
Personally, the dark energy think never made too much sense, but I don't know the math to it, so I can't really judge. :)

Sam5
2005-Mar-03, 01:15 AM
right, but from where do the come?
Well, they appear out of vacuum. :) I realize that's probably not all that satisfying, but the more we look at things at the smallest scale, the more it looks as though vacuum isn't empty space, but rather a roiling mass of virtual particles popping in and out of existence.


Hmm, that sounds like an ether theory.

crosscountry
2005-Mar-03, 02:54 PM
Give me some time, to absorb this and research. I may have another question or two.

Thanks for your help and insight.



right, but from where do the come?
Well, they appear out of vacuum. :) I realize that's probably not all that satisfying, but the more we look at things at the smallest scale, the more it looks as though vacuum isn't empty space, but rather a roiling mass of virtual particles popping in and out of existence. Why is that necessarily worce than suggesting that there's some mysterious "potential" or "field" that "just exists", or that the fabric of spacetime, whatever that is, can be warped. All the models that we use tend to posit the existence of some pretty mysterious aspects of the universe.


they are only virtual because they contain no momentum or energy? how do they transmit information without transmitting energy or momentum? Something has to do that.
No, they're virtual because they can appear "from nowhere". They can carry energy and momentum (either positive or negative) between particles, which is exactly the way particles exchange energy and momentum when they interact by some force. The nature of the forces we observe can be determined from the nature of the interactions. For example, the inverse square law of gravity and electromagnetism follows naturally from this model. The much shorter ranges of the strong and weak nuclear forces arises from the fact that their carrier particles have mass, and so cannot travel as far before the energy they "borrowed" has to be paid back. I realize that I'm speaking in generalities, but the real reason for considering this a viable model is that the results work out in beautiful agreement with experiment.


so, gravitons are like virtual photons?
Virtual gravitons are like virtual photons, carriers of the gravitational force. Real gravitons would be gravitational radiation, just like real photons are electromagnetic radiation. It's just that since gravity is so much weaker, gravitational radiation is much, much harder to detect.


thus, they are not detectible.
The virtual ones are not directly detectable. Real gravitons would be, although we get to the particle/wave nature of things. You'd also want to show that there was a particle-like aspect to them (that is, that a purely wave model wouldn't explain the observations), which is probably trickier than detecting the gravitational radiation in the first place. How do you set up the gravitational equivalent of the photoelectric effect? :)


thus not proveable?
Depends on what you mean by "proveable". No, really. :D We can't directly see any of the subatomic particles we believe exist, we have to infer their existence from interactions. But I think we're all pretty confident that quarks, electrons, photons, and so forth really exist, even if they sometimes have surprising properties. In science, nothing is ever really "proven", but we do have theories in which we have a great deal of confidence.

So what about virtual particles? Remember I mentioned that once they were proposed, particle physicists realized that if there really are clouds of virtual particles around, that should have some measurable effects in things like the magnetic moment of the electron, or the energy levels in atoms. So experimenters checked, and in fact the experiments agree with the predictions that include virtual particles, and disagree with those that do not. I'd consider that strong experimental support.


here's a wrench for you; light passes a nearby galaxy. it is "lensed" as described by Einstein. if gravitons (small particles) were the culprit only some of the light would be bent; the light photons "hit" by the gravitons. the light not "hit" by the gravitons would not be effected, and thus not bent.

To me that is an incosistency in the graviton theory. Unless someone can explain it better to me. ---- How can gravitons effect light in the form of gravitational lensing?
In principle, every two particles anywhere are linked by interacting virtual particles, so we have every single photon interacting with every single particle in the galaxy. And this goes in both directions. Not only are virtual gravitons "emitted" by a random electron, but the passing photon sends out its own virtual gravitons.

So, the way you'd work out the effect would not be to look at some spread of virtual gravitons and figure out the scattering cross section of the passing photons and work out the collision results. Instead, you'd look at the passing photon and each particle in the lensing galaxy. Technically, there are infinitely many interactions that you have to take into account to work out how any two particles will react to each other. This was actually a problem with the early development of the theory, since it looked like you'd always get an infinite result. But it turns out that the more complex the interaction, the less likely it is (more or less), and so it doesn't affect things as much. You can go down as many levels as you need to in order to get results as accurate as you'd like, in principle at least. Then you'd need to look at the next particle in the lensing galaxy and determine its effect, and so on.

That sounds like a heck of a lot of work! And it would be, actually. But just like we approximate relativity and use Newton's mechanics when we can, in order to make the calculations easier, we use approximations of the quantum model when we can. And we can work out corrections from quantum theory and apply them to the classical picture when the results would be nearly classical, but not quite. And again, the agreement with experiment is amazing.

If you want a better discussion of how this interaction model works, take a look here (http://www2.slac.stanford.edu/vvc/theory/feynman.html), for example, to learn a bit more about how the theory applies to electromagnetic interactions. You can find more in-depth discussions with a simple Google search.

Tacitus
2005-Mar-03, 10:31 PM
Hmm, that sounds like an ether theory.

Well, I'm just an amateur, but wasn't ether supposed to be a medium that filled space (like water filling an ocean) whereas the "foam" of virtual particles talked about above is what makes up the basic fabric of space-time. (Maybe someone else can explain this better :) )

Grey
2005-Mar-04, 12:18 AM
Hmm, that sounds like an ether theory.
In what way?

Maddad
2005-Mar-04, 12:48 AM
I prefer the warped space idea of Einstein. the idea of Potential also works for me.Yes, but what's causing space to warp and how? What does it mean to "warp space?"Space-time near a massive object disappears. More disappears the closer you get.

Sam5
2005-Mar-04, 01:25 AM
Hmm, that sounds like an ether theory.

Well, I'm just an amateur, but wasn't ether supposed to be a medium that filled space (like water filling an ocean) whereas the "foam" of virtual particles talked about above is what makes up the basic fabric of space-time. (Maybe someone else can explain this better :) )

The “fabric of space time”? That’s what “makes up” space? Ok. That’s fine.

I’ve been reading a lot of 17th through early 20th Century “ether” stuff, and nobody seemed to be able to agree on exactly what it was. Many of them (especially in the 19th Century) treated it as if it were some kind of “field”. One might today call that a “fabric” sort of thing that “makes up” space. In one book dated around 1704, Newton suggested it might be the “gravity” of the universe (they didn’t use the word “field” back then). It seemed to be some sort of “stuff” or “field” that was needed to explain certain phenomena. I suppose today we could simply call it a virtual ether since whenever a new term needs to be invented to explain things, one can call it just about anything as long as one puts the word “virtual” in front of it. So if you want to call it a “foam of virtual particles,” that’s ok. Maybe we can say “the ether” is a “foam of virtual particles that makes up the very fabric of space-time”.

Now, here’s an important question: Does the “foam of virtual particles” stay put in all of space, or do separate areas of it move through space with the galaxies that contain it? In other words, does each galaxy have it’s own “local foam of virtual particles” that travel with the galaxy, or does each galaxy travel through a fixed universal “foam of virtual particles”? In the space between the galaxies, does it “stretch” if the galaxies move apart? :D

Sam5
2005-Mar-04, 01:31 AM
Hmm, that sounds like an ether theory.
In what way?

Uhh, anything that “fills” space or that exists in all of space or that makes up space or that makes space anything other that “flat out empty”, tends to qualify to be the elusive classical “ether”.

Grey
2005-Mar-04, 01:54 AM
Uhh, anything that “fills” space or that exists in all of space or that makes up space or that makes space anything other that “flat out empty”, tends to qualify to be the elusive classical “ether”.
I'd disagree, since it really doesn't have any of the properties the classical ether was supposed to have. Well, other than "filling all space" (though it really doesn't even do that in the same sense), but the classical ether certainly had other properties attributed to it.


Now, here’s an important question: Does the “foam of virtual particles” stay put in all of space, or do separate areas of it move through space with the galaxies that contain it? In other words, does each galaxy have it’s own “local foam of virtual particles” that travel with the galaxy, or does each galaxy travel through a fixed universal “foam of virtual particles”? In the space between the galaxies, does it “stretch” if the galaxies move apart? :)
I'm not sure this question even really makes sense. I don't think a sea of virtual particles popping into existence can really be said to "move" or "stretch" in any meaningful sense.

Sam5
2005-Mar-04, 01:56 AM
Uhh, anything that “fills” space or that exists in all of space or that makes up space or that makes space anything other that “flat out empty”, tends to qualify to be the elusive classical “ether”.
I'd disagree, since it really doesn't have any of the properties the classical ether was supposed to have. ....but the classical ether certainly had other properties attributed to it.

Name a few of them.

Grey
2005-Mar-04, 02:05 AM
Name a few of them.
Sure. It needed to behave like a solid (millions of times more rigid than steel), since it was responsible for the transmission of transverse waves, but should also behave like a fluid in order to fill space. It should be non-dispersive, incompressible, and continuous. It was assumed to provide a standard rest frame for the universe. I'm not certain some of these mechanical details can be said to meaningfully apply to a sea of virtual particles.

[edited for spelling]

Sam5
2005-Mar-04, 02:27 AM
Name a few of them.
Sure. It needed to behave like a solid (millions of times more rigid than steel), since it was responsible for the transmission of transverse wavesit, but should also behave like a fluid in order to fill space. It should be non-dispersive, incompressible, and continuous. It was assumed to provide a standard rest frame for the universe. I'm not certain some of these mechanical details can be said to meaningfully apply to a sea of virtual particles.

A few years ago I tried reading a few old papers to try to pin down the so-called “properties” of the old “classical ether”. Well, I found that I couldn’t do it, because “the ether” was a general term that could mean just about anything to anyone who used it in a paper or book. Over a period of about 450 years, it had many different properties ascribed to it, whatever the theorist wanted to attribute to it. To some it was like a “fluid”, to others it was like a “gas”, to others it was like a “field”, to others it was like some attribute of “space itself”, not that it “filled” space, but that it was an attribute of space. Others thought it might be an attribute of all mater, including what humans are made of. Some thought it might travel through space with astronomical bodies and it might be “fixed” in space at some distances from the bodies, while others thought it might be fixed in all of space and bodies traveled through it.

A “sea of virtual particles” that “borrow energy from the vacuum” (or whatever they do) seems to fill a general theoretical gap like the one the old “ether” filled (metaphorically speaking, of course). In other words, it did whatever a particular writer claimed it did. It was whatever a writer thought it might be.

See?

A “solid a million times more rigid than steel”, and “a fluid that filled all of space”, are somewhat incompatible concepts.

crosscountry
2005-Mar-04, 02:35 AM
Name a few of them.
Sure. It needed to behave like a solid (millions of times more rigid than steel), since it was responsible for the transmission of transverse wavesit, but should also behave like a fluid in order to fill space. It should be non-dispersive, incompressible, and continuous. It was assumed to provide a standard rest frame for the universe. I'm not certain some of these mechanical details can be said to meaningfully apply to a sea of virtual particles.


ah, but you're virtual photons and virtual gravitons seem to agree with this aether thing

Grey
2005-Mar-04, 02:38 AM
A “sea of virtual particles” that “borrow energy from the vacuum” (or whatever they do) seems to fill a general theoretical gap like the one the old “ether” filled (metaphorically speaking, of course). In other words, it did whatever a particular writer claimed it did. It was whatever a writer thought it might be.
Again, I'd disagree. The verbal explanations may sound vague, but that's because we're trying to describe something that doesn't exactly compare well to the objects that our language was developed for dealing with. The behavior of virtual particles is quite rigorously defined within the framework of quantum chromodynamics.


A “solid a million times more rigid than steel”, and “a fluid that filled all of space”, are somewhat incompatible concepts.
And the classical ether had to have both properties. Issues like this are why physicists started to believe that it didn't exist at all and there must be some other explanation.

Squink
2005-Mar-04, 02:51 AM
the "foam" of virtual particles talked about above is what makes up the basic fabric of space-time. Acck! The virtual particles are a property of space, not space itself. You can even exclude some virtual particles from the space between closely spaced conductors:
The Casimir effect (http://physicsweb.org/articles/world/15/9/6)
Wiki on the Casimir effect (http://en.wikipedia.org/wiki/Casimir_effect)

Grey
2005-Mar-04, 02:58 AM
ah, but you're virtual photons and virtual gravitons seem to agree with this aether thing
Well, they aren't "my" virtual photons and gravitons :), but would you care to try to explain how they agree with the "aether thing"? Sam5 has suggested the same thing, but I don't think he's shown that the two concepts are really similar, except that both could be said to "fill space", but even that's not really in the same sense.

Fortis
2005-Mar-04, 03:35 AM
ah, but you're virtual photons and virtual gravitons seem to agree with this aether thing
Well, they aren't "my" virtual photons and gravitons :), but would you care to try to explain how they agree with the "aether thing"? Sam5 has suggested the same thing, but I don't think he's shown that the two concepts are really similar, except that both could be said to "fill space", but even that's not really in the same sense.
Well, the virtual particles certainly don't define a rest frame in any way.

Tacitus
2005-Mar-04, 04:21 AM
Let me try another way to define the difference between the classical aether and our virtual particle quantum foaminess :)

From what I remember, aether "filled" empty space but matter, e.g. planets, stars, etc. displaced the aether like dropping a ball into the bathwater - i.e. the aether only occupied space that was empty.

The quantum foam (if the theory is correct) is what makes up all of the universe - both matter and empty space.

Am I right? Am I even close?

Tacitus
2005-Mar-04, 04:42 AM
Cool discussion, BTW - I'm learning a lot.

Sam5
2005-Mar-04, 06:07 AM
Let me try another way to define the difference between the classical aether and our virtual particle quantum foaminess :)

From what I remember, aether "filled" empty space but matter, e.g. planets, stars, etc. displaced the aether like dropping a ball into the bathwater - i.e. the aether only occupied space that was empty.

The quantum foam (if the theory is correct) is what makes up all of the universe - both matter and empty space.

Am I right? Am I even close?

I am busy right now arguing a 14th Amendment case before the Supreme Court of the BABB on another thread, but when I have time I’ll dig up some old papers that say the very same thing you just said about the “foam”, that it is “what makes up all of the universe - both matter and empty space.” I’ve got that very concept in some old papers. They didn’t know what it was any more than anyone today knows what this “foam” is. But...... it’s needed. Physics can’t get along without it, whether we call it the cosmic foam or the ether. :D

Now, here’s a question I asked that no one has attempted to answer: Does this “foam” stuff travel through space with individual galaxies, or do the galaxies travel through it when they travel through space?

Sam5
2005-Mar-04, 06:09 AM
Cool discussion, BTW - I'm learning a lot.

"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense." A. Einstien, 1920

The Master Knows. :D

Tacitus
2005-Mar-04, 07:30 AM
Cool discussion, BTW - I'm learning a lot.

"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense." A. Einstien, 1920

OK, but from my vague recollection of the aether/ether (which is it BTW?) scientists determined that the aether was supposed to have specific properties, and that they would result in space looking different (can't remember how) depending on which way you looked (forwards or backwards with respect to the motion of the Earth through space). A bit like detecting the wake of a ship through water.

Are you saying that this was for just one (the most prevailing?) theory about aether amongst many?


The Master Knows. :D

But The Doctor Knows Best!

Tacitus
2005-Mar-04, 07:38 AM
Now, here’s a question I asked that no one has attempted to answer: Does this “foam” stuff travel through space with individual galaxies, or do the galaxies travel through it when they travel through space?

If the quantum foam is really just short-lived virtual particles then if the question even applies I would say the answer is no.

I realise that this is probably not an accurate analogy, but imagine floating in the sea. The water molecules transmit the energy of the waves which can carry you a fair distance, but the water molecules themselves don't move very much.

So I guess what I am trying to say is that the galaxies ride the foam as they travel, but there is no specific portion of the foam that is carrying it along (I guess like an ice skater?)

Grey
2005-Mar-04, 04:32 PM
"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense." A. Einstien, 1920

The Master Knows. :D
This seems to be somewhat the same issue. Perhaps one might consider that general relativity implies an "ether" in the sense Einstein is describing, that space has some physical qualities. However, that really isn't the luminiferous aether envisioned in the 19th century as the medium for transmission of electromagnetism. Such a claim would be like claiming "caloric" does in fact exist, but it's the average speed of the molecules in the substance in question. One could probably make such a claim, but that's certainly not the caloric fluid envisioned as the basis for heat briefly in the 18th century.

Regardless, I'm not sure it's even really relevant to the discussion what general relativity has to say. :o That is, a quantum theory of gravity would supersede general relativity in its description of how things work. Of course, it will necessarily reduce to general relativity as an approximation in the classical limit, just as quantum electrodynamics reduces to classic electrodynamics mathematically when quantum effects can be neglected. But that would mean that what general relativity has to say about "space itself" would be about as relevant as what Newton had to say about space itself. Which is interesting philosophically, to be sure, but probably not relevant from a physical perspective.

Sam5
2005-Mar-04, 04:52 PM
Cool discussion, BTW - I'm learning a lot.

"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense." A. Einstien, 1920

OK, but from my vague recollection of the aether/ether (which is it BTW?) scientists determined that the aether was supposed to have specific properties, and that they would result in space looking different (can't remember how) depending on which way you looked (forwards or backwards with respect to the motion of the Earth through space). A bit like detecting the wake of a ship through water.

Are you saying that this was for just one (the most prevailing?) theory about aether amongst many?


The Master Knows. :D

But The Doctor Knows Best!

The spelling “aether” is the 17th and 18th Century spelling, while “ether” is generally the 19th Century spelling. As I mentioned, different scientists attributed different properties to the ether. In 1873 Maxwell published his electro-magnetic theory of light, in which light was made up of tiny electric and magnetic waves that could travel through space on their own, without a pre-existing electric and magnetic field in space, yet even he referred to the “ether” through which light traveled. Einstein tried to get rid of the need for the ether in 1905, but by 1918-1920 he had brought the concept back, since he (after 1911) believed that gravity fields slowed down the local speed of light somewhat while the lack of gravity fields or weak gravity fields allowed light to speed up a little.

Sam5
2005-Mar-04, 05:17 PM
"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense." A. Einstien, 1920

The Master Knows. :D
This seems to be somewhat the same issue. Perhaps one might consider that general relativity implies an "ether" in the sense Einstein is describing, that space has some physical qualities. However, that really isn't the luminiferous aether envisioned in the 19th century as the medium for transmission of electromagnetism. Such a claim would be like claiming "caloric" does in fact exist, but it's the average speed of the molecules in the substance in question. One could probably make such a claim, but that's certainly not the caloric fluid envisioned as the basis for heat briefly in the 18th century.


The so-called “luminiferous aether” was like a pre-existing “field” in space in which light beams, rays, and waves were little “perturbations” in that field. Little moving wiggles of the field, like sound is moving wiggles in the air. But the Maxwell theory (1873) essentially said that tiny little electric and magnetic waves could be emitted by hot vibrating atoms and could go zipping through space on their own, but he also tended to refer to the “ether” through which the EM fields traveled, yet he never could pin it down and identify it.

The 1887 Michelson-Morley experiment actually considered the possibility that the Stokes hypothesis (1845) was correct, that the earth carried an “ether” through space along with the earth’s surface, and up off the earth’s surface a little distance, and so when MM got the “null” results in 1887, they said in their paper they might need to conduct another experiment at a higher altitude, higher above sea level, like up on some mountain top, because if Stokes was right, the earth-surface-hugging ether might travel with the earth, thereby explaining their “null” result. So they actually tried to get up above the “earth ether” in later experiments conducted high on mountains. But later papers said they couldn’t get a good reading on the mountains because they tried the experiment without the light going trough a vacuum, and the light signals on the mountains wiggled too much because of the atmosphere through which they traveled.

Regarding Newton and Einstein, Newton revised his books two or three times to make some corrections and add some new ideas, and so did Einstein. His “revision” papers have been pretty much “lost” to historians and students until the publication of “The Collected Papers of Albert Einstein” by Princeton Press, starting in the late 1980s. One 1918 paper in which he mentioned the possibility of a gravity-based “ether” was never published in English until 2002, so quite a lot of students and professors over the years were never aware of his later opinions about the possible existence of some kind of “ether” in space. What we really need right now is Newton, Einstein, Maxwell, and Michelson here today, all sitting down together trying to figure out the implications of the modern discoveries made during the past 50 years. Unfortunately, we ain’t no Newtons or Einsteins. :D

Grey
2005-Mar-04, 07:51 PM
The so-called “luminiferous aether” was like a pre-existing “field” in space in which light beams, rays, and waves were little “perturbations” in that field. Little moving wiggles of the field, like sound is moving wiggles in the air. But the Maxwell theory (1873) essentially said that tiny little electric and magnetic waves could be emitted by hot vibrating atoms and could go zipping through space on their own, but he also tended to refer to the “ether” through which the EM fields traveled, yet he never could pin it down and identify it.
I don't think Maxwell thought electromagnetic waves could exist independent of a medium to carry them. He spent a great deal of time trying to develop a mechanical model for such a medium. Of course, these days we think he failed to pin it down because there is no such beast. :) Can you give me a reference, or quote the passage that led you to draw such a conclusion?

Anyway, my point was really just that if one is really determined to call any property inherent in space an "ether", I suppose one can, but I think that may be a confusing choice of terminology, since it's certainly not the ether envisioned by those who proposed it as the medium for electromagnetic interactions. Moreover, the properties that Einstein considered intrinsic to space don't appear to be so intrinsic in an interaction model.


What we really need right now is Newton, Einstein, Maxwell, and Michelson here today, all sitting down together trying to figure out the implications of the modern discoveries made during the past 50 years. Unfortunately, we ain’t no Newtons or Einsteins. :D
Thinking about it, I'm not even certain that would do the trick. Would Newton have been able to accept relativity, let alone quantum mechanics? Einstein never really liked the implications of quantum theory, even though he helped lay the groundwork for it himself. Perhaps it will take someone growing up today, with both relativity and quantum mechanics well accepted, to be able to really understand how the two might fit together. And it seems clear that a quantum view of gravity will be needed to bring the two together, as Einstein himself mentions in the paper you quoted.

Sam5
2005-Mar-04, 10:28 PM
I don't think Maxwell thought electromagnetic waves could exist independent of a medium to carry them. He spent a great deal of time trying to develop a mechanical model for such a medium. Of course, these days we think he failed to pin it down because there is no such beast. :) Can you give me a reference, or quote the passage that led you to draw such a conclusion?



I think you are right about that. I might be getting Maxwell’s own text mixed up with something Einstein said in 1929 about Faraday’s theory, which was:

“The "field" thus provided a conceptual apparatus which rendered unnecessary the idea of action at a distance. Faraday also had the bold idea that under appropriate circumstances fields might detach themselves from the bodies producing them and speed away through space as free fields: this was his interpretation of light.”

Come to think of it, I think Maxwell shared the ideas of Hertz in that they thought of the waves as being “perturbations” in the aether. So, hmm, I guess I like Einstein’s interpretation of Faraday’s idea, but I like Maxwell’s 1873 drawing of two electric and magnetic waves traveling together.

crosscountry
2005-Mar-05, 06:23 PM
Cool discussion, BTW - I'm learning a lot.

"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense." A. Einstien, 1920

OK, but from my vague recollection of the aether/ether (which is it BTW?) scientists determined that the aether was supposed to have specific properties, and that they would result in space looking different (can't remember how) depending on which way you looked (forwards or backwards with respect to the motion of the Earth through space). A bit like detecting the wake of a ship through water.

Are you saying that this was for just one (the most prevailing?) theory about aether amongst many?


The Master Knows. :D

But The Doctor Knows Best!

these gravitons enteract with each other right? when they do they change the course of each. thus the "foam" changes like an aether would.

does anyone disagree with that.

Grey
2005-Mar-07, 02:33 PM
I think you are right about that. I might be getting Maxwell’s own text mixed up..
Ah, no trouble.


...with something Einstein said in 1929 about Faraday’s theory, which was:

“The "field" thus provided a conceptual apparatus which rendered unnecessary the idea of action at a distance. Faraday also had the bold idea that under appropriate circumstances fields might detach themselves from the bodies producing them and speed away through space as free fields: this was his interpretation of light.”
That's an intriguing description.

Grey
2005-Mar-07, 02:38 PM
these gravitons enteract with each other right?
Yes.


when they do they change the course of each. thus the "foam" changes like an aether would.

does anyone disagree with that.
I do. I don't think I've ever heard anyone describe the ether as changing, unless you're talking about things like ether dragging that was proposed to try to explain some of the null results when looking for it. But it's not at all clear to me that self-interacting virtual gravitons will behave in any way like anyone ever suggested the ether would behave.