117,765 reputation
5185314
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 11 months
seen 13 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.


13h
awarded  Guru
14h
revised Is energy content of a system different dependending on the observer?
Add prefix
14h
reviewed Leave Open What is the simplest way to prove the Earth is round?
16h
answered Is energy content of a system different dependending on the observer?
16h
comment If gravitation is due to space-time curvature, how can a body free-fall in a straight line?
@HughAllen: spatially spacetime looks flat. After all, if we measure the interior angles of triangles we always find they add up to 180°. However there is a measurable curvature in time - atomic clocks run at measurably different rates if they are at different elevations.At the risk of oversimplifying, the parabolic trajectories we observe for freely falling objects is almost entirely due to the curvature in time.
17h
revised When objects fall along geodesic paths of curved space-time, why is there no force acting on them?
typo
21h
comment I was told that if the Moon had a retrograde orbit, tides would have a faster rhythm. Why is that?
@Esteis: I did mention just after the first diagram that there are two high tides in 24 hours, but I played this down because I wanted to focus on my main message.
21h
reviewed Leave Closed How much of theoretical physics research involves contemplation and reflection?
21h
reviewed No Action Needed How many times does the ISS celebrate New Year each year?
22h
comment Numerical solution for Friedmann equations
Pulsar's answer to this question may be useful. See also Did the Big Bang happen at a point? and How does the Hubble parameter change with the age of the universe?, which use Pulsar's results to calculate $a(t)$.
23h
answered When objects fall along geodesic paths of curved space-time, why is there no force acting on them?
23h
revised When objects fall along geodesic paths of curved space-time, why is there no force acting on them?
Correct link
23h
comment Problem with sound intensity equation in displacement amplitude form
@aukxn: yes, that's correct.
1d
revised If gravitation is due to space-time curvature, how can a body free-fall in a straight line?
Typo
1d
revised Problem with sound intensity equation in displacement amplitude form
Convert equations to Mathjax
1d
comment Problem with sound intensity equation in displacement amplitude form
@aukxn: the equation $I = P/A$ is always true, but the equation $A = 4\pi r^2$ is only true for a spherical wave. So your equation (2) is only true if the wave is spherical. It would not be true for a plane wave.
1d
answered If gravitation is due to space-time curvature, how can a body free-fall in a straight line?
1d
comment What are some most advanced theories explaining why same charge repel, opposite charge attract?
I've linked a Q/A that answers your question. NB don't take Feynmann diagrams too literally. A literal interpretation would suggest particles can only repel because throwing a ball between two objects makes them move apart. The Feynmann diagram is just a pictorial representation of an equation describing the interaction, and the exchange can lead to an attractive force as well.
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reviewed Close Is deuterium a boson or a fermion?
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reviewed Leave Closed How to simulate 2 AC electrodes putting into a pool in Maxwell3D (ANSOFT)?