77,426 reputation
178166
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 3 months
seen 22 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.


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
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
comment How does negative energy from Hawking Radiation cause a Black Hole to shrink?
possible duplicate of Black holes and positive/negative-energy particles
Apr
5
comment Earth as a conductor and emf produced?
Although the Sun's magnetic field is about 100 times stronger than the Earth's, dipole fields fall off as distance cubed so the Sun's magnetic field is negligable at the Earth. It doesn't make sense to consider that gravitational field of sun as magnetic field by a magnet as the gravitational and magnetic fields are completely different in nature, strength and multipole expansion.
Apr
5
comment Electrostatic and gravitational forces?
You just calculate the electrostatic and gravitational forces separately then add them together.
Apr
5
comment Will my hard-drive wear/damage when I tilt my laptop?
This question appears to be off-topic because it belongs on superuser.com
Apr
4
comment Merger happening tangentially, but dark matter at both sides?
The paper is from 2011. Didn't the dark matter distribution in the link you posted come from the more recent Hubble weak lensing study?
Apr
4
comment Which big bang theory has more assumptions?
...to which it has been subjected. To call it unproven is certainly true, in the sense that experiment could still find a flaw in it, however it is widely accepted as a good description of the universe at least until we get down to quantum scales.
Apr
4
comment Which big bang theory has more assumptions?
@rowanman28: The link between conservation of energy and time shift symmetry is provided by Noether's theorems, but this is hard maths. There is a gentler introduction written by John Baez, but even this is probably out of reach for non-physicists. I can see that it will seem unsatisfactory to you to be told you just have to accept it, but then isn't that true of most of modern physics? GR has so far passed every experimental test ...
Apr
4
comment Heat transfer and temperature difference of 2 liquids
@nemu: see the Wikipedia article for details, though all they do is use a constant called the heat transfer coefficient that needs to be determined experimentally. For a rigorous treatment you'd need to solve the heat equation.
Apr
4
comment How can water evaporate at room temperature?
This is basically the answer I would give. Christoph, would you consider fleshing this out a bit? At the moment it's so brief only people who already know the answer will be able to see what you're getting at.
Apr
4
comment Recoil from a shotgun
@Luke: once the shot has left the gun it has no further effect on you, so facing a wall would make no difference (unless the shot ricochets off the wall and hits you!).
Apr
4
comment Why is superdeterminism generally regarded as a joke?
Luboš Motl is someone I have enormous respect for (just look at his answers on this forum!) but he has a rather sharp tongue and I suspect many physicists would take a more moderate tone. Experimental tests of Bell's inequalities have convinced most of us that hidden variable theories are unlikely, however that hasn't stopped people looking for loopholes. And good luck to them. It's a relatively small part of the science budget to pay some theorists to have a go at it and I don't begrudge them the opportunity.
Apr
4
comment Recoil from a shotgun
@User58220: true, though I have no way of knowing what fraction of the momentum is carried by the gases. In any case, I think this is one of those approximate calculations in which understanding the method is more important than the final result.
Apr
4
comment Pendulum (highschool)
@kecer: I would measure $g$ using a range of different values for $\alpha$, i.e. use different initial displacements. You should see the calculated value of $g$ increase with angle, with the zero angle limit matching the simple formula.
Apr
4
comment Speed of light originating from a star with gravitational pull close to black-hole strength?
@user6972: in GR the speed of light is only locally constant.