101,161 reputation
4146259
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 7 months
seen 9 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.


Apr
6
reviewed Close What prevents an orbiting object from getting a speed which is greater than $c$?
Apr
6
reviewed Approve suggested edit on Why does a cup with 100 g water float when placed on another cup with 50 g of water?
Apr
6
reviewed Approve suggested edit on Why does a cup with 100 g water float when placed on another cup with 50 g of water?
Apr
6
comment Where does the phase difference come from in a Josephson Junction?
@Anupam: why is it dimensionally incorrect? The dimensions seem fine to me. $\sin\theta$ is dimensionless and the dimensions of $I$ and $I_0$ obviously match.
Apr
6
revised Where does the phase difference come from in a Josephson Junction?
Typo
Apr
6
answered Speed cannot be greater than speed of light. How about acceleration? Does it have limit?
Apr
6
comment Order of magnitude
@GaurangTandon: you say we have to be precise, but the whole point is that with an order of magnitude estimate we aren't being precise. We're saying our estimate could be ten times too big or ten times too small. It seems odd to be quibbling about the difference between $3.16$ and $3.17$ when the real value could be as low as $0.31$ or as high as $31$.
Apr
6
answered Orbital motion with varying radius
Apr
6
answered Order of magnitude
Apr
6
comment Can we think of gravity as space itself moving?
@user43783: be cautious about thinking of spacetime as some kind of rubber foam that we can compress or stretch then have it spring back. Spacetime isn't a physical object, it's a manifold equipped with a metric, both of which are mathematical structures. It's really only our coordinate system that's flowing. Having said this, for a white hole the Gullstrand-Painleve radial coordinate would be flowing outwards, so this may well be the case for an evaporating BH. I'd have to sit down and think about it.
Apr
6
comment How does negative energy from Hawking Radiation cause a Black Hole to shrink?
Both virtual particles and antiparticles may have a negative energy or a positive energy. Any negative energy object absorbed by the black hole will cause it to shrink because it decreases the total energy, and therefore mass, of the black hole.
Apr
5
comment Matter vs. Antimatter shortly after Big Bang
One has to admire the extraordinary amount of effort you put into to writing your answers.
Apr
5
comment Dark energy and conservation of energy
@Christoph: I note the question you've linked contains contrary opinions from Phil Gibbs and Luboš Motl. They are both vastly better physicists than I will ever be, so how am I to judge who is right? The impression I get is that whether energy is conserved or not depends on exactly what you count as energy. You would have to concede there is no time shift symmetry, so we cannot simply shout Noether's theorem and wave our arms.
Apr
5
comment Dark energy and conservation of energy
This article by John Baez might be of interest as background reading.
Apr
5
comment How does negative energy from Hawking Radiation cause a Black Hole to shrink?
In GR all matter is treated as energy via Einstein's famous equation $e = mc^2$. GR makes no distinction between matter and energy - both create a gravitational field. Both matter and anti-matter have the same (positive) energy simply given by their mass. A negative energy particle is one that, in effect, has a negative mass, and of course adding a negative mass to a black hole will reduce its total mass. This is a gruesome oversimplification, but if you insist on using the particle-antip[article explanation of Hawking radiation this is basically what happens.
Apr
5
answered Electric impluses inside nerve cells
Apr
5
comment Dark energy and conservation of energy
See the link I've suggested. The FLRW metric that (we think) describes our universe is time dependant and this means energy is not conserved.
Apr
5
comment Dark energy and conservation of energy
possible duplicate of Conservation law of energy and Big Bang?
Apr
5
answered Matter vs. Antimatter shortly after Big Bang
Apr
5
reviewed No Action Needed Equilibrium that is not stable