PDA

View Full Version : structure of universe



Copernicus
2012-Oct-10, 03:18 AM
Lets say we had something that acted with the strength of the strong force. It holds two spheres together that are on the order of 10^-15 meters and they are in contact with radius of 10^-35, 10^-45, or 10^-55 meters without significant deformation. Would that be incompressible enough for the speed of light to be what it is? The force would act, on average from the center of the spheres.

Tensor
2012-Oct-10, 03:54 AM
Lets say we had something that acted with the strength of the strong force. It holds two spheres together that are on the order of 10^-15 meters and they are in contact with radius of 10^-35, 10^-45, or 10^-55 meters without significant deformation. Would that be incompressible enough for the speed of light to be what it is? The force would act, on average from the center of the spheres.

Not quite sure what you are asking here. Are you suggesting something that supports light waves?

Shaula
2012-Oct-10, 05:24 AM
You would need far more info than that. The form of the potential of the force for one thing, so you could work out the restoring force due to a perturbation. The strength of coupling between the 'spheres' and the EM field.

Cougar
2012-Oct-10, 12:50 PM
The strong force works the opposite of what one would expect. When confined quarks are close, the force is small or nil. As they start to separate or wander, the strong force pulls them back together. The wider the separation, the stronger the force. "Asymptotic freedom."

Like Tensor and Shaula pointed out, it's very unclear what you're talking about... and what the speed of light has to do with it.

profloater
2012-Oct-10, 01:13 PM
If you make your hypothetical sphere spin you have the basis for an ATM aether!!!

Copernicus
2012-Oct-10, 01:18 PM
Not quite sure what you are asking here. Are you suggesting something that supports light waves?

Yes something that supports light waves.

Copernicus
2012-Oct-10, 01:34 PM
Instead of the strong force lets say it is as strong as the force of charge.
As far as the speed of light goes, critics of the aether say that in order for the aether to be real, one of its requirements are that it should be highly incompressible. I'm just asking how incompressible.

cjameshuff
2012-Oct-10, 03:16 PM
Lets say we had something that acted with the strength of the strong force. It holds two spheres together that are on the order of 10^-15 meters and they are in contact with radius of 10^-35, 10^-45, or 10^-55 meters without significant deformation. Would that be incompressible enough for the speed of light to be what it is? The force would act, on average from the center of the spheres.

By definition, it would be perfectly incompressible: compression would require deformation of the spheres.

Tensor
2012-Oct-10, 04:51 PM
Yes something that supports light waves.

Well, then you got some problems. Aether has to be a fluid to fill all the nooks and crannies in space and on planets (Unless you're talking about entrainment, but then you have a different set of problems), but it also has to act like a solid, to support the rigidity necessary to allow the speed of transmission. Then there's the problem with any object moving within the aether. You have to give the Aether no viscosity and no mass, otherwise the effects would be noted on the orbits of the planets in the solar system. You also have the problem of energy. We know, for example, that energy from the sun takes 8 minutes to arrive from the sun, to the Earth. During that time, that energy, if the Aether was made of small particles, would have to be contained in the Aether, as it moved from one particle to another. Giving spacetime a much higher temperature than it has. The Aether has to be non-dispersive, otherwise, the waves reaching us would deformed and if so, those particles would have been reradiating the energy. As you are trying to show, it has to be continuous at very small scales, but also transparent. And, as cjameshuff points out, it has to be perfectly incompressible. The other point is that the classical waves that required an Aether aren't really needed for two reasons. Since we have a model that uses photons (Quantum Field Theory) and that Transverse waves don't need a medium. So why bother with an Aether?

cjameshuff
2012-Oct-10, 05:22 PM
Actually, I was pointing out a flaw in his setup: he's assuming the system is perfectly incompressible (by his requirement for no significant deformation), and then asking if it's incompressible enough.

But yeah, just getting a propagation speed equal to c is not enough. Our physical models don't need an aether, our observations show no indications of an aether, the required physical properties of an aether are quite unlike anything in our experience...

Tensor
2012-Oct-10, 05:39 PM
Actually, I was pointing out a flaw in his setup: he's assuming the system is perfectly incompressible (by his requirement for no significant deformation), and then asking if it's incompressible enough.


Doh! I hate it when I misread things, then comment on them..... Mea Culpa.

Copernicus
2012-Oct-10, 06:11 PM
By definition, it would be perfectly incompressible: compression would require deformation of the spheres.

Point taken. Lets say would a compression of 1 part in 10^20, 1^30, or 1^40 be incompressible enough.

profloater
2012-Oct-10, 06:20 PM
The strong force works the opposite of what one would expect. When confined quarks are close, the force is small or nil. As they start to separate or wander, the strong force pulls them back together. The wider the separation, the stronger the force. "Asymptotic freedom."

Another weirdness to contemplate!

Shaula
2012-Oct-10, 08:12 PM
Point taken. Lets say would a compression of 1 part in 10^20, 1^30, or 1^40 be incompressible enough.
Again, it all depends on how it interacts with light, with matter and so on. Your question is so vague as to be meaningless.

Copernicus
2012-Oct-10, 08:30 PM
I don't think I am being vague. One of the problems with an aether is that it needs to be nearly incompressible to obtain the speed of light. How near to incompressible? I don't care about the rest.

Shaula
2012-Oct-10, 08:40 PM
Yes and the details of how light interacts with and passes through the medium is key to answering how incompressible it needs to be.

Copernicus
2012-Oct-10, 09:03 PM
Yes and the details of how light interacts with and passes through the medium is key to answering how incompressible it needs to be.

Pretend that they are like an enormous amount of pool balls packed in cuboctahedron structure. I don't really know how sound would travel through packed pool balls.

Shaula
2012-Oct-10, 09:48 PM
Sound is a longitudinal wave, a compression wave. Different physics to a transverse light wave. Sorry, but the actual precise answer to your question is hugely model dependent.

Copernicus
2012-Oct-10, 11:49 PM
Sound is a longitudinal wave, a compression wave. Different physics to a transverse light wave. Sorry, but the actual precise answer to your question is hugely model dependent.

How about some imprecise answers for different scenarios. I just always heard that the universe would have to be fairly rigid for light to travel through a medium, but never heard anything any more specific.

Shaula
2012-Oct-11, 08:05 AM
Have a look at the Theory section of this page: http://en.wikipedia.org/wiki/S-Wave - follow the link to Lambe parameters. Now do you see why I am not going to do the maths for a full treatment of a range of scenarios for you?

For something to have a S wave velocity of c, in the simplest possible case, we need to use the equation v = sqrt(shear_modulus / density). This gives shear_modulus = 9e16.density. We can sort through this in several ways. Assuming the that medium is as stiff as diamond we can work out its density. That gives us an aether density of 478e9 / 9e16 or 5e-6. Which would mean that the aether contained inside the orbital radius of the Earth would weigh 7e29 kg. This is nearly the mass of the Sun. Which, I think we would notice.

OK so flip this. Our uncertainty in the mass of the Sun is at max 2.4x10^26 kg. Mainly due to our issues with G. But we can be generous and assume that this is a bound for the aether mass. So we have 2.4e26kg over a sphere the radius of the Earth. This is a density of 1.7e-8kg/m3. Plugging that back in we get a shear modulus of 5.3e24. This is about 100,000,000,000 times stiffer than diamond.

All the above are SHEAR moduli and based on a very simple SHO model. The shear moduli are not that trivial to calculate without in depth knowledge of the material's properties and bonding and stuff.

Remember it has to be lossless as well as this stiff, not couple to matter in any noticeable way, not be an absolute reference frame and a host of other contradictory properties. I know you don't want to think about them but they are key to why aether was discarded as a hypothesis.

Copernicus
2012-Oct-11, 07:33 PM
Have a look at the Theory section of this page: http://en.wikipedia.org/wiki/S-Wave - follow the link to Lambe parameters. Now do you see why I am not going to do the maths for a full treatment of a range of scenarios for you?

For something to have a S wave velocity of c, in the simplest possible case, we need to use the equation v = sqrt(shear_modulus / density). This gives shear_modulus = 9e16.density. We can sort through this in several ways. Assuming the that medium is as stiff as diamond we can work out its density. That gives us an aether density of 478e9 / 9e16 or 5e-6. Which would mean that the aether contained inside the orbital radius of the Earth would weigh 7e29 kg. This is nearly the mass of the Sun. Which, I think we would notice.

OK so flip this. Our uncertainty in the mass of the Sun is at max 2.4x10^26 kg. Mainly due to our issues with G. But we can be generous and assume that this is a bound for the aether mass. So we have 2.4e26kg over a sphere the radius of the Earth. This is a density of 1.7e-8kg/m3. Plugging that back in we get a shear modulus of 5.3e24. This is about 100,000,000,000 times stiffer than diamond.

All the above are SHEAR moduli and based on a very simple SHO model. The shear moduli are not that trivial to calculate without in depth knowledge of the material's properties and bonding and stuff.

Remember it has to be lossless as well as this stiff, not couple to matter in any noticeable way, not be an absolute reference frame and a host of other contradictory properties. I know you don't want to think about them but they are key to why aether was discarded as a hypothesis.

Thanks for the answer. I was thinking it would need to be many more orders of magnitude stiffer than diamond. I'll check and review the references. Good luck to Shaula