Intuitionist Maths might help reconcile quantum physics and relativity

Clinamenic

The Wild Drunkard
@Mr. Tea do you know anything about how gravity is understood as quantized on the standard model? I just watched a general audience seminar about gravitational waves from that binary black hole merger, and how LIGO picked up on it, but there's still a ton I don't understand.
 

Clinamenic

The Wild Drunkard
Apparently LIGO detects gravitational waves as fluctuations in space-time, by measuring the dilation of a stable laser beam's wavelength as a proxy for said gravitational wave. And apparently it was a fluctuation on an order 10,000 times smaller than a proton (so 10^-23 m I think). The finest measurements ever done.

One thing I still don't really get is Heisenbergs uncertainty principle, but the engineer at LIGO said that they were only measuring difference in one property of the laser's wave, so the uncertainty could be consolidated into some secondary property what wasn't of concern.
 

Clinamenic

The Wild Drunkard
But I don't understand how the concept of a graviton figures into this. I suppose analogous reasoning can be applied from EM radiation, where there is a quantum of... energy/mass (?) associated with EM waves, i.e that they aren't indefinitely divisible.
 

Clinamenic

The Wild Drunkard
So perhaps the quantum of spacetime malleability is a graviton? I'll look up some encyclopedic answer.
 

Clinamenic

The Wild Drunkard
Doesn't exactly clarify things for me.

In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity. In string theory, believed to be a consistent theory of quantum gravity, the graviton is a massless state of a fundamental string.

If it exists, the graviton is expected to be massless because the gravitational force has a very long range, and appears to propagate at the speed of light. The graviton must be a spin-2 boson because the source of gravitation is the stress–energy tensor, a second-order tensor (compared with electromagnetism's spin-1 photon, the source of which is the four-current, a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.[5]
 

Mr. Tea

Shub-Niggurath, Please
@Mr. Tea do you know anything about how gravity is understood as quantized on the standard model? I just watched a general audience seminar about gravitational waves from that binary black hole merger, and how LIGO picked up on it, but there's still a ton I don't understand.
Gravity isn't included in the standard model. 'Naive' attempts to construct a quantum theory of gravity are non-renormalizable, meaning they can't be used to calculate anything because they give meaningless, infinitely large answers to any calculation you try and do. (Actually it's pretty common for quantum field theories, in their 'raw' state, to produce infinities; this is handled by a mathematical trick called normalization, which cancels these infinities. But - and I'm probably drastically over-simplifying here - attempts at quantizing gravity like any other field (such as the electromagnetic field) yield an infinite number of infinities, which cannot be renormalized away.

So people have tried other approaches, the two most well-known being superstring theory (and an extension of this called M-theory), which is renormalizable but so far has not yielding anything like an actual physical theory that can make any predictions or reproduce the phenomenology that we already understand; and loop quantum gravity, which doesn't assume that spacetime is a fundamental property of existence but seeks to construct it from some more fundamental principle.

There's quite a thorough answer here from a guy who seems to know what he's talking about (i.e. a bit more than me):
 
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Mr. Tea

Shub-Niggurath, Please
But I don't understand how the concept of a graviton figures into this. I suppose analogous reasoning can be applied from EM radiation, where there is a quantum of... energy/mass (?) associated with EM waves, i.e that they aren't indefinitely divisible.
Yes, this is exactly right: the graviton is to the gravitational field (i.e. perturbations in spacetime) what the photon is to electromagnetic fields, which includes light (and radio etc.).
 

Clinamenic

The Wild Drunkard
There's quite a thorough answer here from a guy who seems to know what he's talking about (i.e. a bit more than me):
This was beyond me, but at least I'm better able to identity that which I don't understand.

I'm still at a lot of basic conceptual building blocks here, still trying to get past basic linear algebra so I can understand tensors, still being introduced to discrete differential geometry, still at basic understandings of calculus and trig. And I sense the kind of theory and maths involved in something like quantum field theory, or even special and general relativity, will remain out of reach until more basic understandings are secured.

But aside from that, how do you understand the relation of energy and mass? I gather E = mc^2 is a way of understanding energy and mass in terms of each other, and that changes in the energy of a system slightly effect the mass of the system, but can they be understood as two sides of the same coin?
 

Clinamenic

The Wild Drunkard
I gather E = mc^2 is a way of understanding energy and mass in terms of each other, and that changes in the energy of a system slightly effect the mass of the system, but can they be understood as two sides of the same coin?
The standard model displays the mass of particles in terms of Ev/c^2.
 

Clinamenic

The Wild Drunkard
it doesnt matter Stan, don't worry about it.
Well its largely an effort to think beyond the scientific consensus, to attain such a familiarity with standardized ideas so as to better ascertain how well they apply at certain depths.
 

Clinamenic

The Wild Drunkard
Also, I just find this stuff fascinating, even if it largely is a professionalized artifact of our own cognition. I see it as a modular conceptual framework, or at least thats how I'm appropriating this stuff.
 

Clinamenic

The Wild Drunkard
@IdleRich @Mr. Tea Do you guys know anything about negative mass or negative effective mass? My understanding is that the former is entirely theoretical, but that there have been experiments involving certain quasi-particles that effectively had a negative mass, hence negative effective mass.

I don't understand general relativity enough to really be confident here, but if normal mass is understood to attract other normal mass in its surrounding spacetime, negative mass in theory would repel normal mass? Ignoring the fact that both of the masses below look like earth, the blue illustrates normal mass while the red illustrates negative mass. Other massive bodies in this two-dimensional spacetime would "roll away" from the red, and "roll toward" the blue.

curved_spacetime_one_side.png


There was a better visualization presented in this student seminar from Cambridge University Physics Society. Just imagine the red mass being "underneath" the 2D fabric, as if, from its perspective, it effected the fabric in the same way the blue does - just from the opposite perspective.

 
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Clinamenic

The Wild Drunkard
The concept of negative mass would seem to correlate with such things as dark matter (Is absolute mass a term? including normal mass observable to us, and some possible negative mass?), expansion of the universe, the big bang as being an energy conserving phenomenon rather than an energy creating phenomenon (IE that a bunch of negative energy/mass was created as well, yielding a net energy/mass of zero)
 

Clinamenic

The Wild Drunkard
Haha negative mass in principle could escape black holes, no? Assuming there could ever get to be any inside of one.
 
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