There's an interesting article in New Scientist that purports to describe "seven questions that keep physicists up at night". The list is very heavy on the "deep questions" that tend to percolate around the more esoteric quarters of the high-energy physics world, and not so much on the vast bulk of physicists who (ad Chad and I like to harp on) do physics that's much more directly connected to the real (i.e., observable) world. For instance, it's the question of high-temperature superconductivity probably dominates the dreams of lots of solid state physicists, but it's not on the list. So let's look at the questions and rate them on Matt's AMO Physicist Insomnia Index:
Why this universe?
In other words, "why these laws of physics and not others?". I can't say I worry about this much. The laws are what they are. I hold out zero hope for the idea that only one set of laws will turn out to be mathematically possible.
What is everything made of?
Electrons and photons - wait, you mean there's more? Seriously, it would be nice to know what's what in the world of fundamental particles and fields. But it doesn't keep AMO physicists up at night, since as far as we're concerned atoms are pretty much as small as we need to worry about.
How does complexity happen?
Ah, now this is an interesting question and has lots of bearing everywhere in physics. The trivial answer is "because the mathematics puts it there", but nonlinearity and all the rest of that difficult math is not completely understood despite its vast importance. This one actually registers at a modest level on the insomnia scale for me. (Not literally of course.)
Will string theory ever be proved correct?
Nope. But I wouldn't be at all shocked if it's proved incorrect. In any case I worry about it exactly none, as it affects experimental physics exactly none.
What is the singularity?
What is a singularity, not what is The Singularity. I don't really worry about this, but it's an interesting and important question. We have great mathematical descriptions of gravity and quantum mechanics, but they don't mesh well in the domains where both effects are of similar scale. How to resolve this? Beats me, but I'd say this one at least registers at a small level on the insomnia scale.
What is reality really?
Ok, this is just ridiculous.
How far can physics take us?
The article is a little vague and airily philosophical about this, but I think it's asking how close physics is to being "finished". This isn't a purely hypothetical question. As in chemistry, large pieces of the subject are - if not finished - then at least only in need of some work around the periphery. But I'd say even if the Theory of Everything were found tomorrow, we'd have many decades of work left both exploring its consequences and continuing work in non-fundamental physics. In any case, not worth worrying about.
So of the seven questions, I think two are actually relevant to most physics. Well, it's a start.
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What is a singularity, not what is The Singularity.
Aside from that minor goof, "singularity" is a mathematical term which is quite well defined even if your function at that point is not. Sometimes it's just that your coordinate system includes one, e.g., spherical and cylindrical coordinates have a singularity at the origin. Sometimes, such as when you are dealing with a black hole, there are physical consequences to the singularity. Those physical consequences may be interesting, but the fact that singularities exist is not.
What is everything made of?
If you're a cosmologist pondering the questions of dark matter and dark energy, you should be losing sleep over this one. Particle physicists have their Standard Model which explains that ordinary matter is made of leptons and quarks--maybe if you're looking for some other particles like the Higgs boson, you should be worried about this one. Most physicists have no need to worry, as this has effectively been a solved problem for quite some time.
So for most physicists, only "How does complexity happen?" is worth worrying about. Some of the others are relevant to particular areas of physics (e.g., if you are a string theorist you should be worried about whether string theory will ever be proved correct, or more likely disproved). And if you're losing sleep over the question of what reality really is, it's time to either talk to your therapist or admit that you've trapped yourself in postmodernist thinking.
The title should have been "seven questions that keep theoretical physicists up at night".
what's AMO?
AMO = Atomic/Molecular/Optical physics. It's one of the largest sub-divisions of physics, and includes us laser physics guys.
Where does all the pragmatism come from when asked what reality really is? I don't understand why so many people just label this as being irrelevant. It's like they feel more at ease ignoring this fundamental question. Like it protects their dignity instead of acknowledging their insignificant position as a conscious bag of molecules hurling through spacetime.
Then again, isn't physics all about probing the nature of reality? Reality is out there, and we, as observers, are an active part of it. We use mathematics as an abstract language to develop models and theories that describe what we measure around us. What is wrong with taking this one step further and questioning the nature of what we observe? When at some point in the future it becomes possible to shed some light on this question I would rather want this to be discussed in the realm of physics than that of some pseudo-science, let alone religion. So far the humble opinion of an undergraduate student who still has a lot to learn.
Great blog, by the way.
It's as if this was beamed back in time a decade, to become my agenda.
(1) Why this universe? I address that in my draft paper Nearly Physical Deformations of Quantum Mechanics,
33-page 13,900 word Draft 7.0 of 28 July 2009
(2) What is everything made of? I have addressed issues of dark matter and dark energy elsewhere. My publications focus on, rather, quantum cosmology at a more basic level.
(3) How does complexity happen? I've presented about a dozen papers, some coauthored with Christine Carmichael, or Andrew Carmichael Post, or Philip Vos Fellman, or others, at the International Conferences on Complex Systems. This is a major focus om my research.
(4) Will string theory ever be proved correct? I don't think so. My mentor Richard Feynman didn't think so. But, to hedge my bets, I don't ignore it, and have published on the deepest mathematical questions about Strings (via Ed Witten) and Branes (via Lisa Randall).
(5) What is the singularity? That is in every one one of my papers on quantum cosmology.
(6) What is reality really? That is why I write so many papers on Consciousness.
(7) How far can physics take us? Note the topic of the latest competition into which me, Phil, Chrissie entered our paper:
[PDF] âºThe Fundamental Importance Of Discourse In Theoretical Physics
http://fqxi.org/community/forum/topic/550
PV Fellman, JV Post, CM Carmichael - fqxi.org
The purpose of the following paper is to demonstrate that the âlimits of physicsâ is in a very important way determined by the conceptual framework and language of discourse that we use in describing physical reality.
So, bottom line, all 7 questions keep me up at night. And I'm arrogant enough, or hopeful enough, or self-deluded think that I'm helping to answer all 7. It's fun trying, and the referees have not said to stop...
Perturbational string theory demands BRST invariance to unite the effects of an accelerated inertial frame with those of a massive body. The world line of a body immersed in a gravitational field is independent of composition and structure. All local centers of mass vacuum free fall along identical (parallel-displaced) minimum action trajectories independent of composition and structure. The Equivalence Principle (EP).
Two lumps that vacuum free fall differently falsify string theory (and GR). Einstein, Cartan, and Weitzenböck; 1931; teleparallel gravitation: Opposite geometric parity mass distributions (structure) violate the EP. Quantized gravitations add an odd-parity Chern-Simons term to even-parity Einstein-Hilbert action.
End the EP! Run a parity Eotvos experiment opposing macroscopically identical single crystal test masses of left- versus right-handed alpha-quartz. Glycine gamma-polymorph is better, but kilogram single crystals are not commercial.
Somebody should look.
@2 nailed the flaw in the point of view taken by New Scientist, which is that physics == theoretical physics.
I like your answer to questions 1 and 6. They define you as an experimental physicist as opposed to a philosopher. I am reminded of a really old Bill Cosby comedy bit centered on the science class question "Why is there air?" Asking "why this universe" is in the same category. Bill's answer, to blow up basketballs, is just as good as saying this universe exists so Chad can play basketball after doing some physics.
After all, "reality" is what we study in physics, and our emphasis has normally been on WHAT it is rather than WHY it is. The former is amenable to an experiment question, while the latter is essentially a philosophical or religious question. Anyone who doubts this should tell us exactly how the verification of some specific "theory of everything" would explain why the universe is explained by a single equation that can be solved mathematically rather than, say, three or four very different equations that can be solved mathematically, or why we needed to use mathematics to describe the universe in the first place.
On question 2, you could be thinking about how AMO might use a highly precise experiment to probe the existence of WIMPS or whatever, since precision can often provide a heavier hammer than the next accelerator. Simple example: weak mixing showed there was a Z decades before it was seen at CERN. They even knew what its mass was going to be.
A better question 4 would be "Will string theory ever be testable". Further, if it has no observable effects at the AMO level, string theory is unlikely to affect the answer to question 7. How far physics can take us depends more on developments that lead to higher-Tc superconductors, efficient conversion of light to electrical energy, robust long-term storage of data, and realizing quantum computing. It can take us a long way if we focus on physics, what nature actually does. If not, Houston will be under water, resembling Venice with an oil slick.
I agree that, re: (1) "I hold out zero hope for the idea that only one set of laws will turn out to be mathematically possible."
I have asked this more specifically in other venues: "Is there a hyperplane or other well-defined border between the set of all PHYSICAL Theories and the set of all MATHEMATICAL Theories, both embedded in the Ideocosm (space of all possible ideas)?"
Similarly, in our contest paper we discussed the question of which possible settings of parameters (quantum, relativity, thermodynamics) correspond to consistent/complete models of the physical universe, and
does the geometry of that super-system hint at which theory applies to our universe? We link to deep blog discussions on this by John Baez and Jeffrey Morton.
http://fqxi.org/community/forum/topic/550
"The worthwhile problems are the ones you can really solve or help solve, the ones you can really contribute something to." -- Richard P. Feynman (one of my more famous mentors and co-authors)
"Nothing puzzles me more than time and space; and yet nothing
troubles me less, as I never think about them."
Charles Lamb
I think the problem with some of these questions is that it is like a fish philosophizing about water.
What keeps THIS physicist up at night is the following:
When will we ever learn the winner of the election sweepstake contest?!
âx.¬P(x) does not imply ¬âx.P(x).
I find the "what is reality really?" questions to be pretentious. Almost like a "I'm trying to pull your leg" kind of a question. Reality is the most fundamental thing. Without reality existing, you and I are not here. Reality is a combination of existence and experience. I know that isn't satisfactory for most, but I don't really care. What is reality really? This question assumes that there is something beyond reality that we are not observing that's the TRUE reality. I'd like to see how these people know such things, or the better answer would be they're pulling shit out of their ass.