94,280 reputation
3126233
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 6 months
seen 11 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.


Feb
21
answered Composition of kinetic energy
Feb
21
answered Is it possible to have a negative attraction to gravity just like how magnets with same pole does?
Feb
21
comment How can stars make up 0.5% of whole universe?
@LoganM: good point, thanks :-)
Feb
21
revised How can stars make up 0.5% of whole universe?
Matter is not just baryonic
Feb
21
comment Density of a proton
@UncleAl: true in general but quarks are something of a special case because of confinment.
Feb
21
comment Can space be torn?
@user40752: There are speculative, and I emphasise speculative, theories based on eternal inflation. In these theories spacetime is still continuous, but you get universes of normal spacetime embedded in an inflating spacetime. It is possible for these universes to overlap. Nothing in this theory requires spacetime to be torn. Actually it's quite an interesting area and there are several questions about it on this site.
Feb
21
comment Identifying an optics equation in a code refactoring project
@SteveMoss: oops, yes, well spotted!
Feb
21
revised Identifying an optics equation in a code refactoring project
Correct typo
Feb
20
comment Identifying an optics equation in a code refactoring project
For my next trick I will guess your birthday and inside leg measurement :-)
Feb
20
answered Identifying an optics equation in a code refactoring project
Feb
20
comment What does the $\Delta$ notation mean? E.g. for potential energy: $\Delta U$ vs just $U$? What is the difference?
Potential energy has a global gauge symmetry in that you can arbitrarily define the point at which is is zero. So $U$ is actually always $\Delta U$ because it's the difference from the point where you've set the zero. Given that $U$ is always $\Delta U$ there's no real confusion in dropping the $\Delta$. Just make sure you're using the same zero when you're comparing different potential energies.
Feb
20
comment Can Flow of time become still?
For the avoidance of doubt: as long as the spaceship and the Earth have a constant relative speed the Earth sees the spaceships clock running slow and the spaceship sees the Earth's clock running slow. The situation is completely symmetrical, as of course it must be because all speeds are relative.
Feb
20
awarded  Enlightened
Feb
20
awarded  Nice Answer
Feb
20
comment Why do electrons and protons attract each other?
possible duplicate of Why do same/opposite electric charges repel/attract each other, respectively?
Feb
20
comment How does time dilate in a gravitational field having a relative velocity of v with the field?
@DeepakNath: I've updated my answer to show what happens near the Earth. Re your comment above, we haven't directly observed any black holes yet so we haven't seen the effects on the speed of light. It will be a long, long time before our telescopes are that good. For the time being this is a purely theoretical calculation.
Feb
20
revised How does time dilate in a gravitational field having a relative velocity of v with the field?
Respond to comment
Feb
20
reviewed Approve suggested edit on Wavefunction Problem wrong in solutions manual?
Feb
20
comment Can Flow of time become still?
@mbeckish: yes indeed! For example if you're on the spaceship then in your frame you are stationary and it's the Earth that's moving. In that case you would see clocks on Earth running slowly compared to your clock on the rocket. This is the origin of the infamous twin paradox.
Feb
20
revised What Does it Mean for an Extra Dimension to Have Size?
Incorrect use of the term *geodesic*