141,032 reputation
9242395
bio website ratsauce.co.uk
location Chester, United Kingdom
age 54
visits member for 4 years, 5 months
seen 7 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.


Jan
4
comment How did we come to know that electrons actually 'move' in an atom?
@Sofia: yes, that's exactly what I meant. You describe it very well :-)
Jan
4
comment When does a monochromatic beam of light on a reflective surface get completely transmitted?
user13007, as it stands this is a poor question and likely to attract downvotes. You need to be more precise about what your book says. Maybe edit your question and quote from the book. Or tell us which book and what chapter/section so we can check what the book says.
Jan
4
comment If gravitation is due to space-time curvature, how can a body free-fall in a straight line?
@HughAllen: we've observed light being deflected by the Sun, and because the light isn't travelling in a straight line this would necessarily mean the angles of some notional triangle with that light ray as one side wouldn't add up to $\pi$. However I don't know of any direct measurement of an angular deficit. Given that even the Sun produces only a small deviation in a light beam I suspect the effect is far too small to measure on or around the Earth.
Jan
4
comment Non-reciprocal time dilation
@jdlugosz: have you looked at the calculation in the two questions I link? The acceleration does not enter into the calculation. The time dilation is based purely on a calculation of the length of the trajectory i.e. the proper time.
Jan
4
comment How did we come to know that electrons actually 'move' in an atom?
Swami, the idea of the electrons moving is based on the idea they orbit the nucleus like little planets. This is profoundly incorrect. The electrons are delocalised within an atom. They do not have a well defined position and they do not move in the naive sense of the word.
Jan
4
comment How did we come to know that electrons actually 'move' in an atom?
That's like asking why the planets move round the Sun. Couldn't the planets stay still and the Sun move around the Solar System?
Jan
3
comment Does time invariance conclude conservation of energy?
It's not clear what you're asking. Are you asking how conservation of energy follows from time translation invariance (NB time translation invariance not time invariance)? If so I don't know of an intuitive explanation. You need to go through the maths.
Jan
3
comment Expansion of the Universe: is new space(time?) being created or does it just get stretched?
I've lost track of the conversation. I thought we were talking about the objective reality of GR, my point being that it is a mathematical model and I can't comment on how it is related to objective reality (whatever that is). Hence my point that spacetime is a mathematical structure. But your last comment seems to be asking how to calculate a trajectory, in which case you just use the geodesic equation.
Jan
3
comment Strong sustained magnetic field causes fires in Sicilian town. How can anyone generate this?
The question is too vaguely formulated to be answerable using the laws of physics.
Jan
3
comment What's going on along the “sides” of an Alcubierre warp bubble?
I don't see how this answers the question.
Jan
3
comment Protoplanetary disks, angular momentum and prograde orbits
Asher, I've attempted to clarify your question with a couple of diagrams. If you don't like what I've done please shout and I'll back out the changes. To potential downvoters - please don't downvote if you don't like my edit because that's unfair on Asher. Just shout at me instead :-)
Jan
3
comment Expansion of the Universe: is new space(time?) being created or does it just get stretched?
@brightmagus: I don't know. I can tell you how to calculate their trajectory using the geodesic equation, but to find out why they move you'll need to ask a philosopher.
Jan
3
comment What polarizes a rainbow?
When light is reflected (at any angle other than 90º) from an air-water surface the coefficient of reflection (and therefore transmission as well) is different for light polarised parallel and perpendicular to the surface. That's why polarised sunglasses can remove some of the reflections from lakes or the sea. exactly how it happens for rainbows I don't know, but since a rainbow is formed when light is scattered by water droplets it seems reasonable that some polatisation will result.
Jan
3
comment Expansion of the Universe: is new space(time?) being created or does it just get stretched?
@brightmagus: no. I'm saying that mathematics describes how things move.
Jan
2
comment Expansion of the Universe: is new space(time?) being created or does it just get stretched?
Your second question is a duplicate of Why does space expansion not expand matter?
Jan
2
comment Electromagnetic Waves Speed
This is really a duplicate of several existing questions e.g. Relation between density and refractive index of medium and Why does the light travel slower in denser medium?, but I don't think any of the duplicates have a nice clean answer.
Jan
2
comment If space warps distort moving objects' trajectories, does it mean that static objects are immune to gravity?
@PeterHorvath: yes, I voted to close then changed my mind and decided something could be made of it but forgot to retract my vote. Now it's too late!
Jan
2
comment Can the Alcubierre Drive be explained by Gravitoelectromagnetism?
@user22207: the Alcubierre metric is a straightforward piece of mathematics and is uncontroversial. It requires a stress-energy tensor that contains exotic matter. Sonny White and co have hypothesised that if the universe contains extra dimensions then the curvature caused by a suitably chosen electric field could look like exotic matter in our 4D slice of the higher dimensional spacetime. Their calculations are described in this paper. Most of us would regard their ideas as highly speculative.
Jan
2
comment Can the Alcubierre Drive be explained by Gravitoelectromagnetism?
@user22207: no, the Alcubierre drive is already easy to understand - as metrics go it's a pretty simple one - and I know of no way to simplify it farther. The problem is understanding even simple metrics requires a conceptual leap that requires a lot of work. If you're looking for a simple way in then I'm afraid there isn't one. The good news is that the effort is worth it when the light finally dawns.
Jan
2
comment Bond Angle in a water molecule
The 3' is three minutes of arc i.e. $3/60$ or 0.05 of a degree. Why Feynmann's value differs from modern estimates I don't know.