94,670 reputation
3128234
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 6 months
seen 39 mins 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.


2d
comment Jumping sewer lid - WHY?
Having lifted a manhole cover I'd be surprised if anything short of a hurricane could budge it. They must weigh 50kg.
2d
comment Which interaction violates T symmetry?
Have you checked the Wikipedia article on CP violation? There's a paper on experimental measurement of T violation here.
2d
comment Jumping sewer lid - WHY?
It happens in at least one other place. Correction: two other places. What would we do without YouTube?
2d
comment Minimum separation problem
@user34304: in the centre of mass frame the line joining the two particles always passes through the centre of mass - obviously, because the centre of mass is halfway between the two particles. That means for both particles the force they feel always points towards the centre of mass. So it is as if they are moving in a central field centred on the centre of mass.
2d
comment Minimum separation problem
@user34304: the equation for the trajectory is surprisingly fiddly to calculate. For an attractive force (unlike charges) it's the same equation as for gravity, and Googling will find lots of articles on calculating orbits. Be prepared for some hard work though!
Jul
22
comment How does it seem to be that space/time always equals c?
@Danu: damn, I always get that spelling wrong. Thanks :-)
Jul
22
comment How does it seem to be that space/time always equals c?
@MBN: is the four velocity of light well defined? I've had the impression it isn't because you can't differentiate wrt the proper time.
Jul
22
comment In terms of physics, does the phrase “time slows down” mean the same thing as “things happen more slowly?”
Can you clarify what you are asking? For example are you thinking about the time dilation that happens for objects travelling near the speed of light?
Jul
22
comment How does it seem to be that space/time always equals c?
@JoeBlow: I haven't read Andrew Thomas' third book but in his second book (about gravity) he comprehensively misunderstands the Big Bang, which doesn't bode well.
Jul
22
comment How would an X-ray scanner identify a mirror?
@JoeBlow: ah, yes. Weren't those the ones that could allegedly photograph you naked? With that sort of scanner the (hypothetical) X-ray mirror would appear to be glowing.
Jul
21
comment Frame dragging — is there a “non-tiny” example?
@JoeBlow: if you're interested I've shared a Google spreadsheet with the frame dragging calculations in.
Jul
21
comment Frame dragging — is there a “non-tiny” example?
@JoeBlow: re the bucket, if you put a stationary bucket inside a rotating spherical shell then the frame dragging will start to rotate the water in the bucket and make the surface curve. But your question says: if you have a bucket of water big enough, and spin it, it WILL NOT form the concave shape and that's what I don't understand.
Jul
21
comment Frame dragging — is there a “non-tiny” example?
@JoeBlow: as it happens I did a quick calculation of the frame dragging at the surface of the Sun and also at the surface of Jupiter. Both are about 100 times greater than the Earth, though note this is still only 100 times a ridiculously small number. The average density of a galaxy is so low that any frame dragging effect is effectively zero. To get a significant frame dragging you want a high density i.e. a combination of high mass and small radius.
Jul
21
comment Momentum acceleration in space?
If I understand your question correctly it's similar to Can relativistic momentum (photons) be used as propulsion for 'free' after the initial generation? except that you have a baseball bouncing to and fro instead of a light beam. Is this a fair comparison?
Jul
21
comment How does weight add up to press on things?
@Avva: yes, the compression of the block is related to the applied force by the bulk modulus.
Jul
21
comment My basis set isn't orthonormal?
I did a lot of HF-SCF calculations back in the late 70s, and it was routine to use non-orthonormal bases. As Emilio says it made the calculations slightly more demanding but then that's why God invented computers :-)
Jul
21
comment Could space itself be made out of particles?
I've suggested a question that I think goes some way to duplicating your question. As it stands your question is too broad to be usefully answered here. You might want to Google emergent spacetime or something similar to see what sorts of approaches have been suggested, though this is a speculative area with no well established theories. However I think it's safe to say that there are no (plausible) suggestions that spacetime is made out of particles in any literal sense.
Jul
21
comment Could space itself be made out of particles?
Also related: How does classical GR concept of space-time emerge from string theory?
Jul
21
comment Could space itself be made out of particles?
possible duplicate of Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?
Jul
21
comment How would an X-ray scanner identify a mirror?
@placeholder: in airport luggage scanners?