117,172 reputation
5183312
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 11 months
seen 5 hours ago

Semi retired old time computer nerd who started programming on a Commodore Pet.

Since I'm also active in the Physics forum I should add that I started as a theoretical chemist, moved into solid state photochemistry and finally worked in industry as a colloid scientist. I only became a full time computer nerd in 1997.


Dec
11
comment Is there a field for which neutral particle and antiparticle, can be considered as positive and negative charge?
Sofia, neutrons are bound states of three quarks and they have no net electrical charge because the quark charges balance out. It's like asking if hydrogen atoms could be the source of some field because they have no net charge either.
Dec
11
comment Do the fields exist without electric charges?
@Sofia: the $\pi_0$ is not an elementary particle. It consists of a pair of charged quarks - either $u\bar{u}$ or $d\bar{d}$. It decays to photons because the charged quarks annihilate each other. I suspect you will find in all apparently neutral particles that decay to photons charged particles will be involved somewhere.
Dec
11
comment Length contraction, front middle or back
Note that acceleration of a rigid raises all sorts of interesting issues. See this paper on the Arxiv a discussion. If you're only interested in steady speeds that simplifies things. If so can you adjust your question accordingly.
Dec
11
comment Question on open organ pipe
@DanielSank: yes, and that's the point. As the air expands away from the high pressure zone just outside the tube it's momentum carries it away from the end and leaves a (temporary) zone of below atmospheric pressure. This low pressure is lower than the low pressure in the tube. As this air then rushes back it's momentum raises the pressure to above atmospheric and above the highest pressures in the tube.
Dec
11
comment Why did the big bang explode if there is no oxygen in space?
See Did the Big Bang happen at a point? for what the Big Bang was and therefore why oxygen wasn't needed.
Dec
11
comment Universe from nothing
See Total energy of the Universe. This is essentially a duplicate of your question. The video is pointless because you can't describe the universe without general relativity.
Dec
11
comment Do the fields exist without electric charges?
It's a nice idea, but I can't think of a particle-antiparticle annihilation producing photons that doesn't involve charge somewhere in the process.
Dec
11
comment Does a body curve spacetime at higher velocities?
See also Does a moving object curve space-time as its velocity increases? though the answers to this don't much more than say the curvature is an invariant, as you've already pointed out.
Dec
11
comment Does a body curve spacetime at higher velocities?
possible duplicate of reletivistic mass as seen by different observers
Dec
10
comment Classical Mechanics - Potential Energy Function
It's a long time since I had to sketch a function, but IIRC the steps were: (a) differentiate to find the extrema (b) differentiate again to establish if they are maxima or minima (c) find the zeros (d) find the beaviour at infinity. Once you've got this it's easy to draw a rough sketch of the graph.
Dec
10
comment Wave-Particle Duality in the Confinement of an Electron in a Box
I agree with you. The wavelength of the $n = 3$ state is going to be of order $\tfrac{2}{3}$ times the size of the box. So I don't see how the answer can possible be 0.515nm. I wonder if there's a misprint and the box side should be 0.9nm. In that case you'd expect the answer to be about 0.6nm, which is in the right ball park.
Dec
10
comment Does Zero Point energy imply acceleration?
Dirk, I'm not sure your question as sense, as I suspect you are still thinking about the oscillator as if it was a classical particle. If you express a SHO in momentum space then the ground state is something like $\Phi(p,t) = A \exp(-p^2/2\hbar m \omega - i\omega t/2)$ so it's not a momentum eigenstate, but the momentum isn't changing in any oscilliatory way as it would in a pendulum.
Dec
10
comment Does Zero Point energy imply acceleration?
Re the close as duplicate vote, Dirk's question is clearly broader than just Zitterbewegung, so the question Is Zitterbewegung an artefact of single-particle theory? is not a duplicate.
Dec
10
comment What is the cause for the validity of Newton's third law?
@user36790: When we get down to the quantum regime it starts getting tricky to define what you mean by a force, so classical Newtonian mechanics doesn't apply, or at least not in any simple sense. Apart from such special cases the third law always applies. The question Does Newton's third law apply to momentum or to forces? has more on this.
Dec
10
comment Does Zero Point energy imply acceleration?
See Is Zitterbewegung an artefact of single-particle theory?. Zitterbewegung is not to be taken literally as the particle vibrating to and fro.
Dec
10
comment Why we take product of two such quantities which are proportional to a common quantity when formulating?
This is really a maths question, though to my untrained eye it looks a rather vague maths question ...
Dec
10
comment Why do we use the Coulomb potential for the hydrogen atom?
At the time the nature of the Coulomb force wasn't understood. Maxwell had given a description of it, but not a fundamental mechanism. There was no reason to suppose it wasn't universal.
Dec
9
comment Einstein's space-time theory
The question is allegedly what would happen if you chased a beam of light. I say allegedly because posterity has a tendancy to tidy up the messy business that constitutes research.
Dec
9
comment Why superconductors aren't used in space?
@LouisYang: even on Pluto it's too hot to use superconductors. Possibly deep in interstellar space it might be cold enough, but that isn't much use if you want your spacecraft to start near a star and end near a star.
Dec
8
comment How can black holes have electric charge and spin?
@MurtuzaVadharia: understanding the Kerr metric is one of the more challenging tasks for aspiring general relativists. You aren't going to really understand its structure without a lot of hard work. I'm afraid there is no quick and easy route.