94,275 reputation
3125233
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 6 months
seen 1 hour 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.


Jul
18
comment how to measure the age of light?
See How is distance measured to far away stars and galaxies?
Jul
18
comment Another layman blackhole question, pulling one end of a string out from behind the event horizon
@AlfredCentauri: everyday experience suggests it's possible to dangle weights on ropes in a Schwarzschild metric (well outside $r_s$). If there is a limit beyond which my treatment fails it would be interesting to know more. I'll read the paper you link, thanks :-)
Jul
18
comment How are the distances to the most distant $\gamma$-ray bursts measured?
@M.Herzkamp: yes, exactly.
Jul
18
comment When you measure position of an electron in a energy pure state, what happens to the energy?
I've attempted to expand my comment to a proper answer, but I'm at the edge of my comfort zone here and site members who know more about this area may wish to criticise.
Jul
18
comment matrix elements of the electronic molecular Hamiltonian between a hartree product and a Slater determinant
Is that Szabo and Ostlund's book Modern Quantum Mechanics? If so, what exercise are you referring to i.e. what number?
Jul
18
comment What determines whether a pool ball will bouce backwards after colliding with another pool ball?
It is just the spin. To make the cue ball follow the ball it strikes use top spin, and to make the cue ball move backwards us bottom spin.
Jul
18
comment What determines whether a pool ball will bouce backwards after colliding with another pool ball?
Related: physics.stackexchange.com/q/113923
Jul
18
comment Could Dark Matter particles that don't couple to quarks or leptons have been produced?
@BrandonEnright: any quantum gravity theory is likely to be a unified theory so it would include all particles. For example String Theory includes not only gravitons but all the other known (any many unknown) particles as well.
Jul
18
comment Could Dark Matter particles that don't couple to quarks or leptons have been produced?
@New_new_newbie: yes, it's generally accepted that the Standard Model must be replaced by some more general theory at high energies. The only question is what replaces it, and that isn't currently known.
Jul
18
comment Could Dark Matter particles that don't couple to quarks or leptons have been produced?
@BrandonEnright: For sterile neutrinos I believe there are interactions in SO(10) that can create them so you don't need gravity. I way out of my depth though, so don't take this as gospel. String theory predicts all sorts of particles of this type. They are generically known as hidden sectors.
Jul
18
comment How to find the force to cause certain trajectory?
This question appears to be off-topic because it is thoroughly described in the Hyperphysics section on trajectories
Jul
18
comment How to find the force to cause certain trajectory?
The Hyperphysics section on trajectories has an excellent description of how to do the calculations you describe. This is quite a large page (well, set of pages) but I think you'd find it interesting. You're quite correct that 45° is a special case and gives the maximum range.
Jul
18
comment How many atoms does one need to get reliable crystal information with X ray or electron diffraction?
@YungHummmma: yes, quite true, but you would still (in principle) measure a diffraction pattern from your two atoms. In fact for amorphous systems you do get a diffraction peak corresponding to the nearest neighbour distance i.e. basically diffraction from pairs of atoms.
Jul
18
comment GPS Satellite - Special Relativity
Making up some numbers to illustrate, suppose $1/\gamma_e = 0.8$ for the Earth's surface and $1/\gamma_s = 0.6$ for the satellite. That means when 100 seconds pass for the stationary observer 80 seconds pass on Earth and 60 seconds pass on the satellite. So as seen from Earth 60 seconds pass on the satellite for 80 seconds on Earth, and the time dilation is therefore 60/80, which is simply $\gamma_e/\gamma_s$.
Jul
18
comment When you measure position of an electron in a energy pure state, what happens to the energy?
Yes, energy is exchanged between the electron and the measuring system, so the energy of each changes. The total energy of both the electron and the measuring system is still conserved.
Jul
17
comment Another layman blackhole question, pulling one end of a string out from behind the event horizon
The downvote is surprising. This isn't the clearest answer I've ever seen but everything M. Herzkamp says is true.
Jul
17
comment Does time move slower at the equator?
@michael: yes, but both the observer at the North Pole and at the equator are moving round the Sun/round the Milky way/along with the Milky Way at the same speed, so these motions do not contribute to their relative time dilation.
Jul
17
comment Another layman blackhole question, pulling one end of a string out from behind the event horizon
As long as you stay above the event horizon you can hover above a black hole using a rocket. You don't have to orbit. In fact there is no stable orbit for matter within 3 times the horizon distance.
Jul
17
comment How many atoms does one need to get reliable crystal information with X ray or electron diffraction?
Are you sure the insets were X-ray diffraction and not electron diffraction? Since TEMs can routinely do diffraction measurements it seems more like they were electron diffraction.
Jul
17
comment Queries regarding the peer review process and examples of where it has not worked out
This question appears to be off-topic because it is not about Physics, it's about fraudulent physicists.