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Jan
9
comment Do the arms of a spiral galaxy spin around like a candy bar in long spirals?
Since density wave theory works in 2D, it's not really concerned with this sort of thing. I think the fact that these are density waves rather than matter-transporting waves severs the connection to vortex rings. There might be nonzero coupling to vertical frequency, especially in warped disks, but we've gone pretty far on this tangent already.
Jan
9
comment Do the arms of a spiral galaxy spin around like a candy bar in long spirals?
The OP just edited, and I think (though it's rather unclear) the question is about whether the arms are rolling around their long axis (independent of their traveling around the galaxy).
Jan
9
comment If we forget which slit the photon goes through, does it interfere again?
I'm very confused why there are 4 votes to close a quantum eraser question as non-mainstream.
Jan
7
comment Black hole corona and bipolar outflows
@annav I do believe the chosen answer is off the mainstream. The cited paper is not quite wrong, but it uses language from 50 years ago that is misleading when put in a modern context. The only way you get a speed of light that is not $c$ is if you measure distance and time in different reference frames, and there's never a good reason to do that.
Jan
6
comment Is an x-ray maser possible?
Possible duplicate of Gamma Ray LASER Theory and Technology
Jan
6
comment Physics after a Theory of Everything
Something to ponder: what exactly do you think most physicists do with their careers? I assure you, the vast majority of professional physicists are not working on anything remotely like a theory of everything, despite the publicity such people might get. Most physicists study complex phenomena where we already know all the "fundamental" ingredients we need, but there are still plenty of problems to be solved. Having the fundamental theory in hand won't change their lives in the slightest.
Jan
5
comment How long ago, and how far away, could “A long time ago in a galaxy far, far away” have been?
The Pop III stuff is good, though a biologist might quibble that it took a few billion years for complex life to evolve once Earth formed. In any event, just to be pedantic, distances are somewhat tricky in cosmology. A galaxy at redshift 6 will appear to us as it looked 1 billion years after the Big Bang. When that light was emitted it would only have been 4 billion light years away. Its present position can be extrapolated to be 28 billion light years away, which is outside our event horizon (present-day light from that galaxy will never reach us).
Jan
5
comment How many frames can human eye see?
"Are new 144hz monitors just a marketing trick?" Yes, just like the absurd numbers of pixels you see today, far smaller than the angular resolution of most people's poor eyesight.
Jan
4
comment Can we consider light from the Sun during sunrise and nightfall as polarised?
Nothing to really worry about. Some users have voted to close this question as not conforming to our homework policy; others have voted to leave the question open. If is is closed, we can deal with how to improve the question.
Jan
2
comment Is causality a total order?
I kind of get what you're asking, but I'm curious as to the source of the first sentence. Spacetime is partially ordered, with timelike separated events being comparable and spacelike separated events not being comparable.
Jan
2
comment Light cone argument for speed of light
@GyroGearloose That could be turned into an answer.
Dec
30
comment Can we consider light from the Sun during sunrise and nightfall as polarised?
I'm very confused as to how this is being voted closed as homework. There's really nothing here except a pure concept.
Dec
29
comment What exactly is the 'lift' of a sailboat as explained by Bernoulli principle
The Bernoulli principle applies here as much as to airplane wings (that is to say, not at all). But this is orthogonal to the question of sailing against the wind, which has nothing to do with "lift" (which can be said to be there, though horizontally) and everything to do with the keel.
Dec
29
comment What is the possibility of a railgun assisted orbital launch?
-1: Blasting your way through the atmosphere at orbital velocity is feasible for exactly one thing: obliterating the spacecraft. Also, the pessimism about reusable rockets has proven unwarranted now.
Dec
29
comment What is the underlying physics that makes Li-Fi “100 times faster” than Wi-Fi?
This is all well and good, though I think the OP is getting hung up on the more fundamental concept of the difference between latency and bandwidth.
Dec
29
comment What is the underlying physics that makes Li-Fi “100 times faster” than Wi-Fi?
@Klik Yes, flag for moderator attention and request that. I'll note though that I for one don't see this as off topic here.
Dec
29
comment Why can't gravitational force have repulsive counter part?
@igael Standard inflation is like dark energy: you can draw analogies with a fluid with negative pressure, but still the density is strictly positive. This violates some energy conditions but not the most important ones.
Dec
29
comment Self Teaching QFT
It is impossible to learn QFT, or any advanced topic, starting with nothing. Why do you think we physicists spend years studying introductory topics in school before tackling something like QFT? We aren't idling away the primes of our lives studying centuries-old stuff just to waste time before getting to real research. There's a bit of hubris in thinking you can learn a subject while avoiding all the years of prep work and many textbooks every professional in the world has found to be necessary.
Dec
28
comment From master equation to Fokker-Planck equation
I see that you've made all your answers community wiki. Is there some particular reason? Usually this is reserved for truly collaborative efforts among multiple people (take for example this post), and it deprives you of all the reputation you deserve.
Dec
27
comment Is there a general procedure for covariantizing equations?
As a relativistic fluid dynamics person who works almost exclusively with non-relativists, I think this is a great question. Unfortunately I've never written down an algorithm for how I go about this sort of thing. I'll have to think about it, but perhaps there is something to be said for going into the fluid rest frame...