146,823 reputation
13250412
bio website ratsauce.co.uk
location Chester, United Kingdom
age 54
visits member for 4 years, 7 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.


Apr
12
comment Difference between speed of light and of bullet after passing through a barrier
possible duplicate of How does light speed up after coming out of a glass slab?
Apr
12
comment Lorentz contraction in continuously accelerating rod
See also Bell's spaceship paradox. Searching this site for the phrase will find some related questions.
Apr
12
comment Flat universe and accelerating expansion
This happens because the geometry is defined by the total mass/energy density, but the time evolution of the scale factor is defined by the equation of state of the stuff making up that density. Dark energy has a different equation of state to matter. Specifically the matter density scales as $1/a^3$ while the dark energy density is constant. You might be interested to read How does the Hubble parameter change with the age of the universe? and the links within it.
Apr
12
reviewed Close Maximum Extension of a Spring
Apr
12
reviewed Leave Open Tensor components change under rotation-translation
Apr
12
reviewed Close Direct interaction theory
Apr
12
reviewed Close If the cord has a breaking strength of 25.0 N, explain why the cord broke when supporting a load so much lesser than its breaking strength
Apr
12
reviewed Leave Open Why do we see light and isn't everything dark?
Apr
12
reviewed Leave Open Is it possible to derive the Doppler effect formulas for sound using relative velocity?
Apr
12
reviewed Leave Open Does dark energy work like gravity, but the opposite way?
Apr
12
reviewed Leave Open Increasing the efficiency of solar cell systems
Apr
12
reviewed Close Truck driven from a small motor that can carry a heavy load, yet can travel fast.
Apr
11
reviewed Leave Open Magnets quantum locking/levitating
Apr
11
reviewed Close Is potential energy an energy exists or potentiality of energy?
Apr
11
reviewed Close how much weight can you put on a bike tire?
Apr
11
revised Why can “slow” neutrons trigger fission?
I doubt the cycle is viscous
Apr
11
comment Does a photon emitted in a potential well due to transitions undergoe a blueshift?
@Air: a photon has an oscillating electric field so the net field integrated over time is zero and the net force integrated over time is zero. The instantaneous force is not zero, which is why a radio wave photon can make the electrons in the aerial oscillate.
Apr
11
comment Does a photon emitted in a potential well due to transitions undergoe a blueshift?
@hft: The point is that we are considering an electron in a potential well, not an isolated electron. So the gravitational potential is undefined. For example, if the potential well is caused by a proton (e.g. an electron in a hydrogen atom) then the gravitational potential of the proton exceeds the electron by a factor 2000. If it's a uranium atom the factor is another 238 times greater still. It is certainly possible to calculate the red shift due to an isolated electron (guesstimating how localised the electron is), but this isn't relevant to the question.
Apr
11
comment Does a photon emitted in a potential well due to transitions undergoe a blueshift?
Is that likely to be significant?
Apr
11
answered Does a photon emitted in a potential well due to transitions undergoe a blueshift?