109,681 reputation
5167295
bio website ratsauce.co.uk
location Chester, United Kingdom
age 53
visits member for 3 years, 9 months
seen 8 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.


May
7
comment How to do calculation in relativity of simultaneity
@Graviton: I've edited my answer to show how you calculate the length of the train
May
7
comment Can I measure a journey time < 100 years on a 100 light year voyage?
Re your last comment: maybe this should be a new question ...
May
7
comment Can I measure a journey time < 100 years on a 100 light year voyage?
Aha! The question I was thinking of is Would a fast inter-stellar spaceship benefit from an aerodynamic shape?. This doesn't actually calculate heating, but it does show the effect is small up to 0.999c.
May
7
comment Can I measure a journey time < 100 years on a 100 light year voyage?
If you're on the rocket then from your perspective you're stationary and it's the rest of the universe that's moving towards you. You would indeed see the rest of the universe Lorentz contracted, and that's the point I make in the last section of my answer where the distance to the star decreases because of the Lorentz contraction. I'm sure there's a question on the site about the effect of interstellar dust at high speed - I'll have a search ...
May
7
comment Can I measure a journey time < 100 years on a 100 light year voyage?
Hi Ben. Because we get so many questions like this I wrote the Q/A I've linked to try and produce the definitive article on the subject. Have a look at the linked article and if there are any points still unclear please come back to use with a new question or edit this one.
May
6
comment Special relativity paradox and gravitation/acceleration equivalence
If you want to post this as a question I can demonstrate (using the Minkowski metric) why acceleration doesn't affect the clock rate.
May
6
comment Special relativity paradox and gravitation/acceleration equivalence
In SR inertial frames are defined as having a constant velocity relative to each other i.e. their acceleration is zero. That's why there are no preferred (or to use your term absolute) inertial frames in SR. If you consider accelerating frames then there is a preferred frame i.e. the frame in which the acceleration is zero. Acceleration can be handled perfectly well in SR, but you need to be careful about the calculation.
May
6
comment Special relativity paradox and gravitation/acceleration equivalence
Velocity is not absolute in SR, but acceleration is absolute in SR.
May
6
comment If I had a 1cm iron sphere that I could vibrate at an rate, how fast would it have to be vibrating before it could not perceived by sense of touch?
No. Your finger is prevented from passing through the iron sphere by the exchange force, and vibrating the sphere does not affect this force.
May
6
comment Special relativity paradox and gravitation/acceleration equivalence
Acceleration is absolute in SR, and it is always unambiguous who is accelerating and who is not - the person accelerating is the one who feels a force. That means the assumption in your first paragraph isn't justified.
May
6
comment $D$-brane and 5th dimensions
Have you tried the obvious Google searches? If so, can you be more specific about what you're asking?
May
6
comment does space-time expansion affect on fundamental particle?
possible duplicate of Why does space expansion not expand matter?
May
6
comment Chasing a photon
Should 9.999999999c be 0.9999999999c? You can't travel faster than light. The equation used for the calculation is the relativistic addition formula.
May
6
comment Do you feel more impact force when falling straight down or tipping over?
@LarryHarson: it's one of the classic problems you give students because their initial guess at the answer is always wrong :-)
May
6
comment Can a person at a photon sphere of a black hole decide where the black hole is?
@Anixx: intuition is a dangerous way to approach GR. Have a read through the relevant chapter of the Schutz book (that's the clearest analysis of the problem I've seen) then come back to us with any points arising from it.
May
6
comment Is it possible to achieve the speed of light within frames of references?
Hi LearnIT. I have linked a question that is basically the same as yours. As you near light speed velocities don't simply add together as they (approximately) do at lower speeds. So you can't exceed the speed of light by adding velocities as you've suggested.
May
6
comment How close does light have to be, to orbit a perfect sphere the size and mass of Earth?
If you are a physics nerd (and why else would you be reading this :-) the reasons why your suggestion isn't the case are absolutely fascinating. It's because the radial coordinate $r$ that we use to measure distance from the centre and the time coordinate $t$ change as you approach the event horizon. Sadly you can't really appreciate what goes on without a lot of effort to learn the basics of GR, but believe me it's worth the effort!
May
6
comment How close does light have to be, to orbit a perfect sphere the size and mass of Earth?
@auxsvr: if the Earth was spherically symmetric (obviously it is only approximately so) the gravitational field outside it would be described by the same Schwarzschild metric that describes the exterior field of any sphere of the same mass. The tidal forces at the Moon would not be affected if a spherical Earth were to collapse to a black hole.
May
5
comment Can a person at a photon sphere of a black hole decide where the black hole is?
@Anixx: for an introductory book see chapter 11 in A first course in general relativity by Schutz or chapter 4 in Exploring Black Holes by Taylor and Wheeler. If you're feeling brave the general relativity bible discusses the orbits in section 2.5.
May
5
comment What exactly is an anti-neutrino?
@Yashbhatt: see Identification of particles and anti-particles. It is possible that neitrionos are Majorana particles though I get the impression this idea is going out of fashion.