I see that we are being invited to speculate. (And to buy charge preamplifiers from cremat.com)
marcus said:
here is Bee's top ten
http://backreaction.blogspot.com/2006/07/top-ten.html#my
Unsolved Questions in Theoretical Physics
1) How can the apparent disagreement between general relativity (GR) and quantum gravity be resolved? Does it require to quantize gravity? If so, how? If not, see 2 and 3.
The disagreement is not just "apparent" it is deep and significant. It can only be resolved by unifying the two theories. Both are correct and beautiful in their own domains, but both are getting a bit ragged trying to keep up with the latest corrections. It's time to look for a simple theory that will allow both to be correct, but only in their own domains.
Our primary problem is that in our physics, the concept of time is too simple. Instead of being able to divide time into past, present and future, as is intuitively obvious, our physics is written as if all times are equivalent. Then our savants write books on where the arrow of time comes from. Some of them try to convince us that the past and future are just an illusion. Some of us are convinced.
To try to quantize gravity is a mistake. We do not yet truly know what "quantize" means, so extending the technique to a domain many orders of magnitude away from the domain quantization was developed in will be a waste of effort. What we need to do is to understand quantum systems.
marcus said:
2) Do black holes destroy information? If not, what happens to the matter that collapses to a black hole?
In the sense of GR, yes, black holes destroy information. But GR is incomplete. In particular, GR assumes that there is no universal time. If one can convince oneself of this, then anything is possible, going back in time, etc. The fact that none of this is seen in our world should put pause to the people who believe this, but they seem to have no problem swallowing the claim. You take two theories, GR and QM, and extend them BOTH to way way outside the realms in which they are verified, and then, lo and behold, the result is that you get weird consequences. And this decades after everyone knew that the two theories were fundamentally incompatible. This is not physics, it is barely mathematics.
My guess is that the matter that collapses into a black hole is emitted from the black hole as radiation that travels somewhat faster than light. I don't think that this process conserves energy, in the usual way we measure it (which is based on a physics determined by relationships observed only at very very low energies). I'd tell you how to derive these superluminal particles (see comment on inflation below), but you're too busy and probably know too much.
marcus said:
3) Are there really singularities in GR (inside black holes/big bang)? If so, how can we understand what happens there? If not, how are they avoided?
No, there are no singularities. The density of matter reaches a maximum. To understand what goes on there you need to first understand that we are very small and weak and the universe is very big and made of very sturdy material. Even our whole galaxy is very tiny, and the processes contained in it very weak. The universe is a very tenuous thing.
The reason that physics is simple is because it is all done as linear approximations. The reason linear approximations work so well is that we are very small, our energies are low, while spacetime is very big and its inherent strength is very large. When we use GR to model spacetime, it is GR that gets all non linear and curvaceous, not spacetime.
It used to be known that in QM it was impossible to create a hidden variables theory. The big boys provied it impossible. Then Bohm showed how to do it. Whoooops. The same thing is going on in GR. It used to be known that spacetime was inherently non Euclidean. Now several people have shown that it is possible to get GR on a flat spacetime.
So what should you believe? That moving around matter can alter the spacetime that has existed for billions of years? Or that spacetime is unalterable by the puny efforts of our tiny little galaxy? Now that we have theories that have it both ways you can decide for yourself. No mathematics will make the choice for you. But Occam's razor will tell you that you should assume that spacetime cannot be destroyed until it is proved otherwise to you. Note that it is only if you assume that spacetime is weak enough to be bent by matter that you have to explain how it is that we're not already stuck in a big black hole.
marcus said:
4) How can we explain the data (supernovae, WMAP) which seems to indicate that the universe is filled with dark energy. Is there really dark energy? If so, what is it? Why does it become important just now (coincidence problem)?
When we look at the list of known particles, it is quite evident that there must be some further order that is organizing them. When that order is better known, these issues will likely be resolved.
marcus said:
5) How can we understand the rotation curves of galaxies, and the too large sizes of voids between galaxies. Does dark matter exist? If so, what is it made of?
I'll guess that dark matter does not exist, and that instead, Milgrom is right with MOND. Everyone would love the theory except it doesn't have a theoretical underpinning. As long as QM and GR run around loose in their own restricted domains it will not be possible to derive MOND.
The MOND theory is about how very low accelerations work. An acceleration is a change in velocity. Let's do our QM in a box. Velocities are quantized, therefore changes in velocity are also quantized so acceleration is quantized. Under this assumption, a MOND effect when dealing with very low accelerations is not that surprising.
In QM, when we model a particle in a box, we let the dimensions of the box approach infininity so that the number of velocities become infinite. Or do they. The number of velocities is always countable, but we're hoping that the limit will be an uncountable number of velocities? Nope, mathematics doesn't work like that. And besides, the universe is finite, it is unphysical to take a limit as the dimension of the box goes to infinity.
marcus said:
6) What happened in the very early stages of the universe? How can we solve the horizon/flatness/homogeneity problem? Did inflation really take place? If so, what is the inflaton? How does electroweak symmetry breaking work? Where does the baryon-antibaryon asymmetry come from?
Inflation is the solution for the homogeneity problem. Inflation is the natural consequence of assuming that the usual elementary particles are composite and the preons travel faster than light. I'd show you the mathematical details but you either don't have enough mathematical sophistication or you are too busy.
When physicists talk of electroweak symmetry breaking, the underlying assumption is that of perturbation theory. The world is inherently non perturbative, and looking at it through perturbation colored glasses causes some serious confusion. The assumption of symmetry breaking in the elementary particles is that these particles should all be equivalent at high enough energies, and it is only in the cold conditions now seen that the symmetries are lost. The assumption is that the "vacuum" can choose anyone of a number of orientations, and that the choice of orientation determines which particles are which.
You are too busy for me to explain to you why it is that the vacuum is an unneeded artifact of QM. Ask Julian Schwinger's ghost if you don't have the time for me to explain it to you. The short description: the vacuum state only exists to the extent that you convince me that you can split a density matrix state description into a state vector state description. I can demonstrate at great length that the density matrix formulation is superior, for example see:
https://www.physicsforums.com/showthread.php?t=124904 but this will have little effect because you are too busy and know better.
The primary disadvantage of the state vector formalism is that it gives you great freedom to define the internal symmetries of your particles. This means that if you want to suppose that the structure of the elementary particles arises from simpler subparticles, you have to look through huge numbers of possible types of subparticles. Geometric density matrix theory is very very restrictive and leads you to a unique solution. But again, you have very little time.
So a result of analyzing the elementary particles from the point of view of state vector formalism is that there will always be huge amounts of unphysical (gauge) freedom running around. One of the features of that sort of freedom is that you can convince yourself that relationships that, in fact, are very discrete and exact, are instead, continuous. The principle of symmetry breaking is one of these.
As an example of the very (unpredicted by standard model) discrete relationships between the elementary particles, take a good look at the current experimental limits on the MNS matrix. Is that the result of symmetry breaking? As long as you assume it is, without specifying what it is that the symmetry breaking comes from, you will always have billions of ways of describing the particles.
The baryon / antibaryon asymmetry comes from the fact that spacetime is an elastic solid. In an elastic solid, vibrations consist of regions of higher and lower densities. So long as the vibrations are very small (i.e. our current low energy regime) the two types of vibrations are symmetric. But at high enough amplitudes, the symmetry is broken by nonlinearities in the elasticity.
In an elastic medium, there are always two classes of moving waves, longitudinal and transverse. The longitudinal waves always travel faster, typically by a factor of about sqrt(3). In spacetime, the transverse waves travel at the speed of light. The longitudinal waves are too high energy to be commonly observed, but were responsible for the inflationary era.
marcus said:
7) Why do we experience 3+1 dimensions? Are there extra dimensions? If so, why haven't we yet noticed them?
There is one hidden dimension. Tightly curled up, it corresponds to proper time. Have we noticed it? Of course. Einstein noticed it in 1905. Why don't more physicists believe in it is a better question.
As soon as you work through the consequences of a single hidden dimension, with the assumption that matter and energy consists of waves in the elastic medium defined by that manifold, you can derive the special theory of relativity and a good bit of quantum mechanics. But rather than do this, isn't it better to forget about proper time, and instead develop two different theories, QM and, from SR, GR, that are incompatible? We wouldn't want to put any theorists out of business here.
marcus said:
8) Are the electroweak and strong interaction unified at high energies? If so, are the currently known particles of the standard model (SM) elementary? Are there more yet unobserved particles? Why are the parameters of the SM what they are and are they in yet unknown ways related to each other (or are they related to 1. or 6.?). Why are the gauge groups of the SM what they are?
No, the hope that the strong and electroweak interactions are unified at high energies is a result of the hopes and dreams of perturbation theory. The currently known particles are not elementary. They're not even one stage away. The parameters of the standard model are exactly determined by the physics of the interactions that bind the particles of which they are composed.
The gauge groups arise from the splitting of density matrices into spinors. Density matrices already eliminate the U(1) gauge symmetry. Suitably generalized, one can similarly eliminate the other gauge symmetries. To get them back, simply split the generalized density matrix back up into spinor form. Hey, you're too busy to understand this.
marcus said:
9) Can we understand quantization?
Yes. Most literally, quantization is the process that takes a wave and allows it to be interpreted as a particle. This is the measurement process. But to understand it, we have to step outside of time as it is used in physics, and instead contemplate time as it is felt by observers. That is, we have to think of time as separated into past, present and future. The wave function is the event as it exists in our future. The particle is the event as it exists in our past. The measurement is the process of evolution of the universe that allows an event that was in the future, to become a part of the past. Note that this evolution is not the unitary evolution of QM, which has only to do with how one evolves a wave state at one time to a wave at another time.
marcus said:
10) What causes particles to have masses and why are these so much smaller than the Planck mass (and hence the gravitational interaction so weak, alias the hierarchy problem)?
The fundamental particles should have Plank mass energies. Binding two particles into one produces a new particle with a mass less than the sum of the masses by the binding energy. If the binding energy is on the order of twice the Plank mass, then binding two Plank mass particles together will give a deeply bound composite particle with very low mass.
A group of Plank mass particles are bound together. The result has a lower mass than the Plank mass, and this is caused by its having a smaller strain on spacetime. A number of such groups can then combine again, possibly creating a new bound state that has even lower energy. The process continues, with each new hierarchical level having lower characteristic energies.
The hierarchy between the masses of the particles mostly arises from density matrix theory. In density matrix theory, only the spin-1/2 particles have clean and simple geometrizations. That suggests that using a scalar Higgs particle to give mass to the leptons is unrealistic.
To replace the Higgs with a spin-1/2 type particle, you must make it as an effective scalar, and that means replacing the usual bilinear mass term with a doubly bilinear mass term:
m h \psi^\dag \psi \to m^\dag m \psi^\dag \psi
In the above, note that in going to a purely spin-1/2 formalism we hope to lose the arbitrary constant mass term. The result is that instead of masses of elementary particles being simple, the square roots of their masses are simple. This gives the Koide formula, which can also be expanded to cover the neutrinos (i.e. predict the neutrino masses):
http://www.brannenworks.com/MASSES2.pdf for example.
Carl
