Since time slows down as you approach the speed of light is a photon created and destroyed at the same time, from its point of view?
Yes, but not because of its clock. For observers like us, the photon’s time appears frozen. For the photon itself, time progresses normally. However, the distance it measures between creation and destruction is zero. So, either way, the photon doesn’t experience any passage of time, but the reason is different depending on who you “ask”.
I’ve wondered that, too. It certainly makes parts of quantum mechanics more “intuitive” if photons can be thought of that way, if anything about QM can be said to be intuitive.
Alas, the less intuitive parts of QM remain so even if you invoke the above special relativitistic effects.
What is your preferred reference text for current Standard Model theory?
There is no single catch-all text, really. I have a shelf full of references I can hit depending on the particular thing I’m after. For many topics, I might seek relevant review articles or original papers. If I want a quick refresher on some subject, the Particle Data Group’s biennial “Review of Particle Physics” has excellent (and concise) reviews on theoretical and experimental topics. M. Peskin and D. Schroeder’s QFT text is good for a rigorous treatment of core standard model topics.
But, again, no single source covers all areas well, so when I need a reference, I usually look in many places. (If your question was aimed at eliciting tailored recommendations, let me know.)
I just noticed this thread…
Yeah, I probably wouldn’t have noticed it either. I read General Questions regularly, but I rarely find myself in MPSIMS. I think there are many with this same M.O. who might be interested in the discussion if they stumbled upon it.
"About a quarter of the universe seems to be made up of matter that we cannot see and whose nature we are unsure of." “The universe also seems to made up of matter, not antimatter. We’ve got to explain that.” Can you clarify these two statements, since they seem slightly contradictory? Is there evidence that dark matter is actually matter and not dark anti-matter? Or is “matter” simply sloppy terminology for what would be better called “dark mass”?
The use of “matter” is the first statement is the sloppy variant (i.e., matter vs. antimatter is not specified.) However, the conundrum in the second statement remains even given the presence of dark matter, since we still look out and see no evidence for, say, antimatter galaxies. Neverminding what dark matter might be, the underlying issue is that the universe doesn’t seem to be treating matter and antimatter symmetrically. (Also, if the hope is to recover the missing baryonic antimatter in the form of dark matter, that fails since we don’t see the annihilations that should occur constantly in the galactic halos or occasionally in intergalactic space.)
We aren’t completely in the dark on dark matter. That is, we do know some things it can be and some things it can’t. Importantly, most of the dark matter doesn’t seem to be baryonic. A large baryonic contribution is inconsistent with the distribution of galaxies and the observed cosmic microwave background fluctuations; and it would lead to atoms (or at least electrically charged particles) in the dark matter halos that should be visible but are not seen.
The large-scale structure in the universe is consistent with so-called “cold” dark matter, which really just means “heavy” dark matter (that is, the dark matter particles need to have been non-relativistic sufficiently early in the universe’s evolution). This nixes the light neutrinos as DM candidates. Favored candidates include hypothetical bosons called axions (which stem from a certain class of standard model extension) and the somewhat generically named “weakly interacting massive particle” (or WIMP). Supersymmetry offers WIMP candidates naturally, as long as they are stable in the model. (Unstable particles are not viable DM candidates since they would have decayed away by now.)
Is there any indication that dark matter interacts with regular matter in any way besides gravitation?
Not yet, and you are correct that such interaction is necessary if we are to learn anything.
What is your opinion of dark matter theory in general? Personally, it reminds me of the epicycles the Ptolemaic model needed to explain the motion of the planets. An extra entity, in other words. Do you think any other theories explaining intra-galactic motion have merit?
Dark matter doesn’t seem too far-fetched to me. The standard model has thrown lots of hints our way that new physics is occuring at energy scales relevant for candidate dark matter particles. Additionally, the amount of dark matter implied by galactic rotation curves is consistent with what comes independently from global fits to cosmological data (e.g., CMB anisotropy). Regarding alternatives: I haven’t seen any compelling ones yet.
Do you have any knowledge of the experiments being done looking for a minimum length scale for gravitational interactions?
Only a little. Anything specific on your mind? I can say for certain that they haven’t found any evidence of deviation from 1/R[sup]2[/sup] yet, but you already knew that. 
A few physicists call c Einstein’s constant (following the precedence of Planck’s). I prefer that term myself, but not enough people know it, so it hinders communication at this time. But it doesn’t hurt to put the idea of the term out there. Maybe someday enough will switch over.
Good luck! “Einstein’s constant” doesn’t roll off the tongue quite as well as “spee-da-lite”. I’ll usually just say “c”, actually, like I might say “h-bar” or “e”.
) completely different from my schooling. It’s good to have threads like these; I wish we had more science specialists doing them.
)
In the first example you’re presuming a faster-than-light cause and effect, which violates Special Relativity. In the second example, you’re presuming that one ball was black and the other was white “all along”; this would be the case if the