Speculation Without Evidence

While most have clear experimental signatures we would recognize, 2 & 3 may fall into the category of not even wrong.

1. I'll say "no".

2. Sure, if you count regions of spacetime carried off by eternal inflation so that they're inaccessible from our local patch.

3. Defined broadly, "string theory" includes such topics as the exploration of strong-coupling regimes in condensed-matter physics via gauge/gravity duality and the modelling of nuclear interactions, so in one sense, a "string" exists every time two quarks are pulled far enough apart. In the more narrow sense of fundamental strings, I'd say. . . sure.

4. I doubt we'll ever find one, but a theory which ends up verified on other grounds might include them as a necessary ingredient.

5. Yes.

6. Yes.

My very uninformed answers:-

1. No
2. What if they did?
3. Judgement reserved, but probably 'barking up the wrong tree'.
4. No
5. Probably not
6. Yes

One is actually true, but barely. When you mix quantum mechanics with special relativity, the uncertainty principle implies that there is a nonzero (albeit exponentially suppressed) amplitude for a massive particle to leak outside its forward light cone--that is, to be found further from its initial position than allowed by the speed of light. The effect is random and cannot be used to transmit information, so causality is preserved.

Nonetheless, this phenomenon is responsible for many features of relativistic quantum theories, including the impossibility of defining a basis of well-defined position eigenstates, the necessity of antiparticles, the phenomena of particle creation/annihilation and of indistinguishable particles, the spin-statistics connection, and the CPT theorem.

See, for example, Weinberg's discussion of antiparticles in one of the early chapters of his 1970's book Gravitation and Cosmology.

My understanding of #2 (if by saying multiple universes, you're including the Many-Worlds interpretation of quantum mechanics) is that it's a logical consequence of decoherence and the observations we've made regarding the wavefunction. (There's a link at the top of that entry to the entire series on Quantum Mechanics, if you're looking for more background on where he's coming up with those ideas).

1) Achieving absolute zero is prohibited through division by zero, same as a massed body may not propagate at lightspeed. Large negative temps Kelvin are trivially accessed (e.g., the active medium in a laser pointer, MRI imaging). Interested readers may suggest a like loophole in Special Relativity.

2) Outside our lightcone, as mentioned.

3) Perturbational string theory has at least one empirically falsifiable founding postulate - BRST invariance uniting the effects of a massive body and an accelerated inertial reference frame. Somebody should look (pdf).

4) Easy! Take a ferromagnetic thick-walled hollow sphere. Magnetize it with one pole interior and one pole at the surface. Everybody then says "Gauss' law!" but nobody ever does it to find out.

5) No Higgs, no SUSY, no string theory (no quantized gravitation overall if containing the Equivalence Principle or surrogates like BRST invariance).

6) Sure, but no naturally formed black hole can be warmer than its surroundings. No natural black hole can decay. The real test is making LHC black holes when it smashes accelerated heavy nuclei. The interaction is hot but the vacuum is cold.

1. A way for a massive object to beat the light speed limit?
As #4 above suggests, the real question is transmitting information FTL. I say no. The universe seems to be working real hard to prevent this. The time-travel paradoxes alone!

2. Any type of multiple universes?
As Eric says, this has to be true if you buy the multiple universe description of, say, quantum computing. However, I think that calling different components of the wavefunction different universes is ridiculous. It's the equivalent of calling other galaxies other universes, which was done for a while.

But I say yes; other universes in the cosmological sense do exist. How to detect them...

3. Strings as described by string theory?
Either strings or something even crazier. It'll come down to what is meant by "exist." By the definition "be very useful as a concept" then yes. By the definition "and not be an approximation to an even deeper theory", I'd never bet on that.

4. Magnetic monopoles?
Nope. They don't feel like things that would exist.

5. The Higgs boson?
Yep. Mass has to come from somewhere.

6. Hawking radiation?
Yep. Let thermodynamics be your guide to the unfamiliar.

Actually, black hole solutions to the Einstein equation with magnetic charge exist, and so will inevitably arise as virtual states in perturbation theory. Cluster decomposition then implies that these magnetic monopoles must exist as features of any quantum theory that includes gravity, although we are nonetheless extremely unlikely to see one as a real state any time soon.

This is entirely apart from the issue over whether solitonic monopole solutions can arise from spontaneous breaking of a GUT symmetry in the early universe down to SU(3)xSU(2)xU(1) of the Standard Model.

1) Yes, because it makes life more interesting. Probably will require weird conditions (like Casimir vacuum).

2) Don't care.

3) Probably.

4) Yes.

5) Sure.

6) Yes.

Well, (2) is conclusively YES. Proof at http://scienceblogs.com/dispatches/2008/11/hinderakers_delusions.php

1) Normally I'd say "no" however, I heard from a grad student I know that Fermilab possibly found some evidence for tachyonic particles recently. Jury's out but it doesn't seem too plausible (a significant portion of the people at Fermilab dismiss the evidence)
2) I'd have to say this is a complete unknown.
3) See above.
4) IIRC, it was Dirac that demonstrated charge would be quantized if a single magnetic monopole existed, though I'm quite skeptical.
5) Extremely likely
6) I didn't even though this was debated?

1) Theoretically yes (Alcubierre drive), practically no.
2) There exist half a dozen (or more) hypothesis about this but nothing that can be proven.
3) There is a reason string theory is still only a hypothesis (or a group of them)
4) Theoretically they could exist, realistically no.
5) They are trying to prove it's existence now. It would be more interesting if they can't find it.
6) Yes. Based on the existence of black holes that is.

"I didn't even though this was debated?"

It's not really, but since it hasn't actually been observed yet we shouldn't take it as a given.

1) Yes. Any massive object will do. Just wait long enough. Oh, you meant in a controlled fashion? Probably not (even though faster than light travel would be freaking awesome).
2) Given that there are many different hypotheses that fit this description I'm almost inclined to say yes. I'd give small probabilities to each but the chance that least one is correct seems substantially higher.
3) I don't know enough to even begin to speculate.
4) No. If they did exist we should have seen them by now.
5) Hrm, probably a yes?
6) The normal thing to do here would be to go for yes. However, I wouldn't be at all surprised if further complications require corrections to Hawking's estimate for the expected radiation levels.

"4) Easy! Take a ferromagnetic thick-walled hollow sphere. Magnetize it with one pole interior and one pole at the surface. Everybody then says "Gauss' law!" but nobody ever does it to find out."

I feel like there's a subtle and interesting reason why this shouldn't work. I'm too tired to figure out where the problem lies. High flux of returning magnetic fields in between atoms in the crystal lattice?

1. Yes, relative to another point in the universe far enough away from each other that the expansion of the universe moves them away from each other faster than light. Other than that, possibly through a wormhole, but not intact.

2. I don't think I buy the many worlds QM multiverse in a physical sense, but I can see bubble universes.

3. No opinion.

4. According to the standard model?

5. I think so.

6. Not sure.

1. FTL: Yes. Inflation caused the universe to expand FTL. Universe contained massive objects. Therefore...

2. Multiple U's: Yes. Either there's multiple universes, or someone constructed this universe, or we got really, really, lucky with this one.

3. Strings: Feh. I like my spacetime loopy, not stringy.

4. Monopoles! I got your monopoles right here, fella. You peddle that stuff around here, and I swear to God I will cut you.

5. Higgs. No. W's and Z's have mass. Just deal with it. Maybe the weak force is not gauge-invariant, ever think of that?

6. Hawking Radiation: Obvious. Steven Hawking's body temperature is 98.6 just like the rest of us. Bodies at that temperature radiate strongly in the infrared.

I've seen a couple people here say they "don't buy" the QM many-worlds interpretation, and Matt rated it pretty low on his probability list - I'd be interested to see a post explaining why, or comments from those who don't buy it explaining why that is. Do you instead accept the collapse postulate, which is (via Eliezer Yudkowsky) "the only non-linear, non-unitary, non-differentiable, non-local, non-CPT-symmetric, acausal, faster-than-light phenomenon in all of physics"?

I'm obviously not an expert on this stuff, and only studied Physics recreationally past the 200-level "Atoms and Nuclei" in college, but I'd be interested to see a reponse to Eliezer's argument, because it seems to me that his has a higher probability of being right than any other explanation I've seen.

1. No, if it is speed relative to the particle it just interacted with. Yes, with cumulative interactions, each new particle's push giving a higher speed relative to the first push. But because the speed of a particle can only be measured relative to the particle it last hit, it will never be *measured* higher than c.
2. No. However a single measurement doesn't determine *one* universe. After a measurement, there is still a multiplicity of universes that could describe reality.
3. No, not as described by string theory. Yes, if those strings are represented by vector-shaped particle: a little arrow or a needle. This visualization fits perfectly with the quantum-mechanical postulates.
4. No.
5. No, but the idea behind the Higgs boson is OK: a particle that gives inertia to the particles it interacts with.
6. I have no opinion on Hawking radiation.

It is impossible to have *all* the evidence. Even mathematicians don't have *all* the evidence (Hilbert didn't know about Godel's theorems until Godel proved them). Thus we are forced to guess the best theory from a limited amount of evidence. This makes all theories biased towards available evidence, but presumably there is a Most Rational Thinker who can deduce the most accurate theory from an incomplete set of evidence.

I'll forgo the embarrassment of guessing difficult questions in a field in which I am, unfortunately, very ignorant, but I second Eric in his favorable mention of Everett's interpretation.

1. How massive an object are we talking about here? More massive that a photon, then no. Less massive, well of course. Of course, this answer relies on how mass arises. :)

2. Yes, and no. Keep in mind that in an infinity of multiverses there will be locations where there exists multiverses where multiverses are impossible. This is because in every theory of physics and cosmology there must be at least one thing that isn't intuitive.

3. Nope, not even close. But further advances will not be possible until researchers accept the fact the basic building blocks of the universe cannot be as busy as superstrings are said to be.

4. What Higgs Boson? Mass arises at an even more basic level.

5. Well of course. The universe is as it is not to please us.

Check out the new theory on string theory. Google Thor's Anvil Revealed and find out what holds the universe together. I use a comprehensive model that includes most of the phenomena found on earth which is explained only seperatly from each other. The model includes what structure causes gravity, dark matter, dark energy, lightning, thunder, (which is the mainstay of the book), rainbows, snowflakes and red sprites which in its self defines the strange name and principal of Kite Lightning (the holy grail of science) which must be present for a red sprite to be generated and shot high into the atmosphere.

The part about how a red sprite defines kite lightning didn't make it into the books first printing but hopefully will be in a magazine or blog soon. If I could figure out how to get this blog to post it I would gladly let you print it. Charles E. Schirmer