Well there's the following evidence, I think... 1. Universe is expanding due to "unknown" repulsive force. Aether? 2. Light bends around massive bodies (where aether could be warped, having a variable density due to the presence of matter?) 3. EM gravitational frequency shift near massive bodies (density of warped aether affecting wavelength?) 4. Physical matter oscillates less as it travels faster through aether, hence time dilation illusion. 5. Physical matter oscillates less the closer it is to a massive object. Is this where aether is denser? If we can't detect something, it doesn't necesarily mean it's not there.
The concept of curved or warped space is simple to understand when viewed mathematically, although the concept is counter intuitive. In pure 3D geometry, the Pythagorean is valid in a Euclidean or flat space. DeltaDistance3D[sup]2[/sup] = DeltaX[sup]2[/sup] + DeltaY[sup]2[/sup] + DeltaZ[sup]2[/sup] DeltaDistance2D[sup]2[/sup] = DeltaX[sup]2[/sup] + DeltaY[sup]2[/sup] In a curved or warped space, the above formulae for distance are incorrect & more complex formulae must be used. In the above, DeltaX, DeltaY, & DeltaZ are the differences in the coordinates for two points. DeltaDistance is the distance between the points. The above concept is not too difficult to visualize for curved 2D spaces like the surface of a sphere. One consequence of the failure of the Pythagorean theorem on the surface of a sphere is that the interior angles of a triangle do not add up to exactly 180 degrees. The concept is far more difficult for our intuition when dealing with a curved 3D space, but the mathematics is not much more difficult than for curved 2D spaces. A convenient method of expressing the laws of physics introduces the concept of an event which occurs at (X, Y, Z, T) & allows the laws of physics to be analogous to the geometry of a 4D space. This is a convenience, not a necessity. For a flat 4D space time continuum, the interval between events is given by the following formula. DeltaDistance[sup]2[/sup] = DeltaX[sup]2[/sup] + DeltaY[sup]2[/sup] + DeltaZ[sup]2[/sup] - DeltaT[sup]2[/sup] The above assumes that the units are such that the speed of light is one. Otherwise, the formula is DeltaDistance[sup]2[/sup] = DeltaX[sup]2[/sup] + DeltaY[sup]2[/sup] + DeltaZ[sup]2[/sup] - (c*DeltaT)[sup]2[/sup] Special Relativity uses the above for the distance between events. It is assumed that gravity does not exist or that it is too weak to have an effect. Special Relativity applies to events occurring in the void between galaxies. General Relativity takes gravity into consideration & similarly expresses the laws of physics using the concept of an event occurring at (X, Y, Z, T). The formula for the distance between events is more complex, indicating that the laws of physics with gravity included are analogous to the geometry of a curved Space-Time continuum. Note that using mathematics which views the laws of physics as analogous to the geometry of a curved 4D space-time continuum is very convenient, but not necessary. Saying that gravity warps space is actually jargon relating to the mathematics used. You do not have to believe in curved space or that gravity warps space to deal with the laws of physics. It is merely a convenient model.
The fact you put a question mark at the end illustrates my point. Who knows what's causing the universal expansion? Is it the aether? Is it the Lion King? I could throw a million ideas out there but they're all useless if they can't be used to make testable predictions. Besides, the concept of the aether doesn't match with the experimental fact that there are no preferred rest frames in physics. Again, not only are you yourself treating this as tentative speculation, but there are further issues that arise here. If an aether is somehow dragging particles so as to deflect them in a gravitational field, why does the effect not vary with particle mass? Why does an iron ball accelerate the exact same way as a feather? Einstein's model explained it with no ambiguity or difficulty, because to him gravity was a property of spacetime itself. To do the same thing with aether, you'll have to start making things incredibly complicated in order to take all these issues into account. How could the aether be producing this frequency shift without actually altering the speed of light? Besides, Einstein was able to calculate redshift as a relativistic effect, using the Equivalence Principle, well before the full equations of GR came about. As it turns out, the redshift is just the right amount to preserve energy conservation. How would you account for precise energy conservation in a model of gravity that involves stuff moving through an aether? Wouldn't the aether have to absorb at least some of that energy? Doesn't explain why, by all indications, time dilation is a mutual phenomenon. If an object in space is coming towards me, they see my clock dilated and I see their clock dilated, and there are ways of performing measurements to prove this. When accounting for the relativity of simultaneity, there's no paradox in having a situation like this, so the question becomes how you could preserve such a property in the aether model, so that time dilation depends entirely on relative velocity and not on some preferred frame of reference with respect to the aether. Not only does physical matter oscillate more slowly in a gravitational field, but every other movement matter makes is also slowed. A dense aether slowing particles down so much ought to have other noticeable effects. Besides, why does a more dense aether not refract and alter the speed of light? Sure, and you can say that about every single idea that's ever been proposed. No reason to think the Lion King is causing time dilation, so we don't bother concerning ourselves with his business.
“Energy density of space” expresses the idea that all space contains energy and the density of a point in space is always fluctuating. The thinking is that energy radiation permeates all space in the form of emitted waves. There are many waves traversing any point in space at all times and so the energy density of any point in space is always fluctuating as a result. If true that would constitute the energy background of space. Where ever mass exists it would be within the energy background.
Well it's not the Lion King who is responsible for expansion so I guess that leaves us with the aether as the culprit. Do you have any better ideas than the Lion King? And I don't think that an aether has anything to do with preferred reference frames unless you consider a static aether model. What makes you think that light would propagate along an aether based medium in the same way that sound does in air? Light has some mysterious properties which we don't understand at all. What if light, for instance, turned out to be a standing wave which sets itself up and vibrates across the aether. Far fetched? So is quantum physics. The fact is that you and I don't know. In modern physics it is a mystery why gravitational mass is identical to inertial mass but if you invoke an aether and present that as the reason for inertia then things become simpler. Higgs field anyone? To me, it seems perfectly reasonable to suggest that an aether (whatever it is) is responsible for inertia. What else causes inertia? And an aether with a repulsive force against itself and mass too would have a tendency to push adjacent masses together into one. That, to me, sounds like a reasonable idea for what gravity actually is. Perhaps the light speed DOES slow down but we can't detect it because ALL mass within the vicinity (including ALL measuring equipment) would have slowed too, hence everything appearing the same. But why should we expect the aether to absorb the energy when we don't even know what it is! We have no idea what exotic properties it might have. There are weirder things out there! Well first of all I don't believe that time exists at all - but let's not go there in detail! I believe that the universe is pure energy, nothing more, nothing less. Matter is just a particular form of energy which we happen to be able to interact with and measure. Time is a tool used to measure one energy event against another and I see no reason why invoking an aether field would necessarily change anything. You just replace Einstein's space-time with a more realistic approach, a solution which would be responsible for gravity, inertia, time dilation etc. It does refract the light and it probably DOES affect the speed but we wouldn't be able to detect the speed change due to some mysterious illusion which is going on. I mean, there has to be an answer to all these mysteries, doesn't there?
How do you know it's not the Lion King? Or, more specifically, what are the properties of the Lion King that rule him out as the cause of the Universe's expansion? No, I don't really expect an answer to that... it's just a lead-in to thinking about the properties of things. What's the difference between the aether and spacetime? What properties does the aether have that spacetime doesn't have?
Well, there's inertia for a start. Nobody has suggested that space-time is the cause of inertia. A physical aether might be a better bet, perhaps. And then there is gravity. The warping of space-time is a consequence of mass, according to Einstein, but space-time doesn't account for gravity. Invoking an aether "substance" could easily account for gravity, given the right properties, i think. Have you seen the main article in the New Scientist again this week? Sorry, no link, but it describes how the light from distant events has been slowed due to what they believe could be a "frothy" aether type substance pervading the universe. I haven't time to explain at the moment but they believe there is plenty of evidence to suggest that light is being slowed by this substance over large distances.
There's a paper that I've linked to before that states that theories with an aether are unstable. It's by Carroll, Dulaney, Gresham and Tam. spacetime does a fantastic job accounting for gravity, unless you are trying to ignore reams of experimental evidence that demonstrates that GR is the correct classical theory of gravity. New scientist quite often contains theories that are highly dubious simply so they can put a pretty picture and provocative headline on the cover. You're much better off reading a book, or a journal article if you want to get at real physics.
Hi Prometheus. I think I remember that paper if it is the one I link below: http://www.sciforums.com/showpost.php?p=2234607&postcount=52 “We investigate the stability of theories in which Lorentz invariance is spontaneously broken by fixed-norm vector "aether" fields. Models with generic kinetic terms are plagued either by ghosts or by tachyons, and are therefore physically unacceptable. There are precisely three kinetic terms that are not manifestly unstable: a sigma model $(\partial_\mu A_\nu)2$, the Maxwell Lagrangian $F_{\mu\nu}F^{\mu\nu}$, and a scalar Lagrangian $(\partial_\mu A^\mu)2$. The timelike sigma-model case is well-defined and stable when the vector norm is fixed by a constraint; however, when it is determined by minimizing a potential there is necessarily a tachyonic ghost, and therefore an instability. In the Maxwell and scalar cases, the Hamiltonian is unbounded below, but at the level of perturbation theory there are fewer degrees of freedom and the models are stable. However, in these two theories there are obstacles to smooth evolution for certain choices of initial data.” That is one link that you have used in the past. Is it the one you are referring to? It does suggest that some aether models are unacceptable or unstable under certain circumstances within the bounds of certain models and theories. But not all alternative aether ideas fall into the referenced models and for you to link to a paper that most of us cannot see how it does what you say it does is short of an adequate refutation of all non-discontinued aether models. The superseded aether theories that have failed to survive rigorous testing are not the sum total of all aether ideas. Undetectable aether ideas that have the energy background and the nature of mass and gravity connected have not been tested yet. Current ideas like gravity waves for example link mass and gravity and utilize the energy background in a way that might make it possible for mass to be connected across any distance of space. Gravity waves emitted by mass are the subject of well funded ongoing research performed by mainstream scientists, satellites loaded with instruments, etc. At some point the benefit of discussing aether theory in the Physics and Math forum gets played out. Speculative ideas come into play that try the tolerance of the established posters and moderators in hard science forums so moving this to a soft science forum like Pseudoscience might allow for a more robust discussion.
Thats the paper I was referring to, yes. My reading of the paper implies to me that theories containing the particular type of aether that they are studying (fixed-norm vector "aether" fields) can never be stable because terms in the Lagrangian are either manifestly unstable or contain hidden instabilities as they show. Of course, you could posit that the aether is not of the type they study, but you're really just developing a more complicated model to replace one we already have that works pretty well.
I read it the same way. And as you know from our unpleasant exchanges, I do posit a different kind of energy background that is not separate from mass and gravity, but that is connected to mass and gravity in a way that requires better technology than we have to detect. That makes it speculation. That makes it Pseudoscience and I realize that you and other professionals understandably have little time or patience with speculators like me. I don't often post in the hard science forums for that reason, knowing that I can't talk back to professionals in their forums with the same latitude as I can talk back in Pseudoscience. It is foolish to defend speculation in a hard science forum, but it is expected in Pseudoscience Please Register or Log in to view the hidden image!.
Ok, let's speculate for one moment that there IS an aether of some sort. And let's say it has certain key properties, one of which is causing the aether to repel against itself and hence cause the expansion of the universe. If this were true, there would be universal pressure applied to all mass in the universe during the phase of expansion. This universal pressure might be very weak but could be enough to cause mass to drift together. The analogy here being the rubber sheet with two ball-bearings placed on it and the rubber finding equilibrium only when the two balls have come together. Does this not seem a reasonable and simple explanation for gravity?
Not exactly. If you want to start a thread with this post in Pseudoscience I will speculate with you about it but you are clearly outside of Physics and Math and well into my territory (speculation upon speculation beyond the patience of the professionals Please Register or Log in to view the hidden image!).
If it's a universal pressure why does gravity always act toward the centre of mass? Why would it cause mass to drift together?
And why does expansion have to be due to a repulsive force. Why couldn't expansion be due to hight energy density surrounded by low energy density? Wouldn't the high energy density appear to expand as it equalized with the low energy density?
Ideas that seem to be reasonable and simple explanations for things are a dime a dozen. Shadow gravity and Scott Adam's expansion gravity immediately spring to mind. It's not really interesting until the idea is defined precisely enough to make real predictions. For example, it's not enough for an idea to suggest a cause for "mass to drift together". If it's going to compete with GR, the idea has to be precise enough to explain measurements of: Newton's universal law of gravitation, the precession of planetary orbits, the Shapiro time delay, the (lack of the) Nordtvedt effect, and the orbital mechanics of binary pulsars.
Those measurements don't say how gravity works. GR says space and time are coupled and that there is a correspondence between math and reality where every point in time is an event and every point in space has a place in the geometry of spacetime that links mass and energy to those point time events. But it doesn't say that the correspondence between math and reality is perfect; the math corresponds to the reality but the math is not the reality itself. That leaves the quest for a cause of gravity open IMHO. Or do you disagree?
Several issues emerge from this thread that can be discussed best in Pseudoscience. There is the OP which is flawed as has been pointed out by the responses. We have the issue of whether aether is still possible even though the old aether theories have failed based on experiments and testing. That view is supported by Carroll, et al. when speaking about certain models making aether theories unstable as Prometheus points out. And we have the issue of why aether ideas won’t go away even though we have GR which adequately describes the effects of gravity. That issue has to do with the correspondence between math and reality which comes up when we view GR as a mathematical construct like Pete mentioned that does the best we can do to describe how gravity works but fails to actually capture the cause of gravity itself. And we have the issue that because we don’t know the cause of expansion it could be aether or it could be the Lion King behind it as CptBork points out, but the link between expansion, aether and repulsive gravity as proposed by WarpTraveler has no support. WarpTraveler then responded to the replies and moved the question to the nature of space itself. This is a rich set of issues. Space could be empty but there is no empty space if light is traversing all space since light is electromagnetic waves, energy waves which fill all space. The possibility that gravity is caused by waves, i.e. that there is a gravity aether, not EM but waves of an as yet undetected nature that would add another constituent to the composition of space. The correspondence between math and reality then comes into play. If space and time are physically coupled into geometry then points in time are events and spacetime connects mass, energy, space and time in a physical geometry of all points in the universe where each point is fixed in the fabric of spacetime. Mass occupies its current point in spacetime and the EFEs describe how that mass will move, i.e. which point it will move to next. If that is reality then as the universe itself increases in the volume there is new space added as expansion proceeds.That would make the universe occupy all space but space would be a finite and changing commodity. The choice seems to be between GR being a perfect correspondence between that geometry of spacetime and reality, or GR is not a perfect correspondence between the two and so there might be aether gravity. The Lion King option is fantasy but the GR and aether options are valid considerations. Is spacetime physically composed of a discrete point lattice or is space filled by energy waves where the energy density of any point in space is continually fluctuating as a multitude of such waves traverse each point in space from all directions? Aether ideas remain because the cause of gravity and the effects of gravity are different issues. There are aether-like ideas that haven’t been tested and for which any experiments proposed are difficulat with existing technology. They won’t go away, there may be some basis to them if GR’s isn’t a physical reality, and if there is gravity aether it might be inseparable from the cause of mass itself. That possibility suggests that there is as yet undisclosed physics that cause mass to be able to maintain its presence within the wave nature of the gravity aether, and as it maintains its presence it would emit gravity waves as a result. Possible energy density limits and thresholds could be elements of that undisclosed physics which nature might employ to serve as the gatekeeper between mass and energy. Those limits and thresholds could enable quantization of energy with mass being composed of energy in quantum increments. Is that any more fanciful than the idea that GR is a reality consisting of a physical point lattice of spacetime and a set of equations that describe how mass moves from point to point in that geometry?
No, they don't. But any theory of how gravity works must accurately predict those measurements. Vague theories that don't make specific quantitative predictions are, as I said, a dime a dozen. I completely agree. Although, perhaps some might quibble that the real quest now is for the cause of spacetime, which is in turn the cause of gravity. After all, any replacement for GR must closely mimic its effects at classical scales.
