DreamsOfAFinalTheory
Dreams of a Final Theory (Steven Weinberg)
- Very good. A lot of my particle intro/PGSS lectures are based off of this book (Although I think I got them from his other work)
- Arrows of science.
- Our science is ABOUT the discovery of explanation built into the logical structure of nature.
The 20C for a physicist begins in 1895 with the discovery of X-ray. Not so much b/c they were important in and of themselves, but because they encouraged physicists to believe that there was much more to be discovered.
- Chalk, calcium carbonate consists of countless fossil shells of tiny animals that lived in ancient seas.
- Chalk strongly absorbs in the UV and IR, not the visible. Light reflected from chalk has pretty much the same distribution of visible wavelengths as the light that illuminates it. This is why chalks (or snow, clouds) are white.
- Its not clear if the universal and the historical elements of science will forever remain distinct. It is possible that eventually the initial conditions will appear as part of the universal laws. (The reverse may also be the case, that what we think of as universal laws may be from historical accidents.)
- The principles of thermodynamics could be deduced mathematically by an analysis of the probabilities of different configurations of the system. Thermodynamics is more like a mode of reasoning than a body of universal law. We can use the same techniques where ever it applies. But the justification of why it applies must be based elsewhere. In terms of the image of arrows of explanation, thermodynamics is like a certain pattern that gets repeated again and again in very different contexts. The fact that a theory finds applications in a wide variety of phenomena does not imply that it is autonomous from deeper physical laws (emergence depends on the deeper physics)
- "It is not unreasonable to hope that when the objective correlatives to consciousness have been explained, somewhere in our explanations will be something that that we recognize something that corresponds to our experience of consciousness itself.
- Something is real when the thing must be taken seriously b/c it can affect us in ways that are not entirely in our control and b/c we cannot learn about it without making an effort that goes beyond our own imagination.
- One of the great services of the tapestry of arrows of scientific explanation is to show that there are no autonomous sciences (eg: astrology /telekinesis).
- B/c there is no time to test everything we should focus on the unknowns that are scientifically plausible. Our greatest aid is the pattern of scientific explanation.
- Reductionism is a sense of hierarchy. It is not a guideline for a research program, but an attitude toward nature. The perception that scientific principles are the way they are b/c of deeper scientific principles (and historical accidents) and all principles can be traced to one simple set of connected laws.
- Elementary physics is more fundamental not because it is mathematically more profound or more useful in other fields but only that it is closer to the point of convergence of all our arrows of explanation.
- Example of why elementary particle physics more fundamental (high-temperature super-conductivity vs electro-weak symmetry breaking). Condensed matter and high-energy physicists will ultimately solve these problems, when they do we will find that high-T super-conductivity is ultimately explained in terms of KNOWN properties of electrons photons and nuclei. However electro-weak symmetry breaking will NOT be explained in terms of other known entities in the Standard Model.
- The study of quarks and electrons is interesting not b/c everyday matter is made of them, but b/c studying them will cause us to learn something about the principles of physics. Actually often exotic particles can be more interesting to HEP. At this moment in science studying particles is the way to make the most progress toward the final theory.
Everyone is really a reductionist. IF a new cure for a disease were suggested by experience with many patients, it would not be fully accepted if we could not see how it could possibly be explained reductively in terms of biochemistry and cell biology. The reductionist attitude provides a useful filter that saves scientists in all fields from wasting time on ideas that are not worth pursuing.
Quantum Mechanics was important more for changing the kinds of question we are allowed to asked than for answering outstanding questions that we had.
- The fact that the motion of bodies in a gravitational field is independent of the nature of the bodies suggested to Einstein that gravitation might be a property of space itself. The fact that gravity depends on mass and on nothing else appears rather arbitrary in Newtons theory, in GR it is a requirement.
- In QM the state of the whole system including the human is described by a wave function that evolves deterministically, in fact more deterministically than Newtons laws because the equations are linear and thus too simple to allow chaotic solutions. However if everything happens deterministically how can there be any uncertainty about the outcome of a measurement ? Where do the probabilities come from? (Weinberg: This is the most important puzzle in the interpretation of QM) Many worlds (with decoherence) explains why the two histories do not interfere, but not (according to Weinberg) the appearance of the probabilities. It is truly surprising how little difference all this makes: in fact it is so irrelevant that one begins to suspect that all the deep questions about the meaning of measurement are empty, forced on us by our language. ("I admit to some discomfort in working all my life in a theoretical framework that no one fully understands" – Weinberg)
- It is striking that it has so far not been possible to find a logically consistent theory that is close to QM, other than QM itself. The failure to find a plausible alternative to QM, even more than the precise experimental verification of linearity, suggests that QM is the way it is b/c any small change would lead to absurdities.
- Wave functions are real because it is useful to include them in our theories. (Just like quarks and symmetries are real)
- One of the effects that contributes to the extra procession of Mercury is the extra gravitational field produced by the energy in the gravitational field itself.
- It appears that anything you say about the way that theory and experiment MAY interact is likely to be correct, and that anything you say about the way that they MUST interact is likely to be wrong.
The importance of symmetries is more important in QM than in classical physics. What makes one electron different from another? Only its E, p, and spin; aside from these every electron is the same. All these properties are simply quantities that characterize the way that the QM wave function responds to symmetry transformations. Matter thus loses its central role in physics: all that is left (beyond the menu of particle types) is principles of symmetry and various ways that wave functions can behave under symmetry transformations.
- The (local) symmetry among different frames of reference requires the existence of gravitation. In the same way another local (internal) symmetry between electrons and neutrinos (and up and down quarks etc.) makes the existence of the photon, W and Z necessary.
- Proteins are built up from chains of amino acids, there are only twenty amino acids that are important in plants and animals. The genetic code is a mess. Its not as bad as a randomly chosen code, but any engineer could design a better code.
The Platonic solids furnish a prime example of mathematical beauty; the same sort of beauty as the Cartan catalog of all possible continuous symmetry principles. In modern physics we dont associate anything to the Platonic solids, but we do believe in a correspondence between different possible kinds forces and different members of the Cartan catalog of all possible symmetries. Where Kepler went wrong was not in using this guesswork, but in supposing that the planets are important.
- "The unreasonable ineffectiveness of philosophy"
- In science (as in politics and economics) we are in danger from heroic ideas that have outlived their usefulness.
- Duration in time is the only thing we can measure by thought alone.
- The idea that quarks and gluons can never in principle be seen in isolation must be the Ernst Mach's worst nightmare.
- The SMs arbitrary features are the menu of particles, ratio of particle masses, and the symmetries. (We currently have bad explanations for why these are the way they are.)
- Broken symmetry is a very Platonic idea. The reality we observe in nature is only an imperfect reflection of a deeper and more beautiful hidden reality, that has all the symmetry of the theory.
- LHC legacy: Prior to the LHC we were not actually sure that the EW symmetry is broken by the vacuum value of some field or that there is a Higgs particle. Something had to do it, but it could have been an indirect effect of some new kind of extra-strong force that doesn't talk to the matter we have seen so far.
- The convergence of the arrows of explanation suggests there is a final theory. (Can we conceive of a theory that gets simpler and more unified without a finite regression of fundamental layers? )
- The Plank energy is roughly the chemical energy in a full tank of gas.
- The only way for science to proceed is to assume there is no divine intervention and see how far you can get with this assumption. It is a profoundly important discovery that we can indeed get so far with out divine intervention. Strong evidence against it.
- Arguing about big science vs small science is a good way avoiding thinking about the value of the individual projects.
- Without the SSC we shall lose a generation of high-energy physicist to Europe or Japan (Seeing the real cost of the SSC loss is being paid now)