147,143 reputation
13250412
bio website ratsauce.co.uk
location Chester, United Kingdom
age 54
visits member for 4 years, 7 months
seen 10 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.


Aug
18
comment Is there a proof that space expanding produces observers at all points that see what we see?
@Timaeus: your answer is quite correct. The metric is independant of $x$, $y$ and $z$, so it implies homogeneity. My point is that homogeneity was an assumption made when deriving the FLRW metric in the first place, so of course it implies homogeneity.
Aug
18
comment Impossibility of time travel due to energy conservation?
@pela: any even remotely sensible approach to time travel requires following a closed timelike trajectory. This is just a path through spacetime, so at any point you would be able to see where you were going and make sure you didn't miss your destination. When you talk about missing Earth I'd guess you're thinking of time travel as some form of discontinuous jump, but no time travel mechanism we know of works like that.
Aug
18
comment What is the wavelength of a hot metal when its temperature 400 C?
Actually I agreed with Daniel's comment and added the first line in response to it. I just didn't admit it :-)
Aug
16
comment Do black holes have a puff pastry point?
Why the downvote? This seems a perfectly good answer to me.
Aug
16
comment Way of measuring thickness of a glass
@MichaeleCastle: If you just have $\theta$ you cannot measure the thickness or refractive index of the glass.
Aug
16
comment Why is any number divided by 0 is infinite?
Hi Aneek. This is a maths question and should be asked on the Mathematics SE. I've just had a quick look and I see it has already been answered on the Math SE here.
Aug
16
comment Way of measuring thickness of a glass
@MichaeleCastle: $x$ isn't unknown. You shine your laser through the glass and measure the angle $\theta$ and the displacement $x$.
Aug
15
comment Way of measuring thickness of a glass
@MichaeleCastle: the problem is that the equation for $x$ is a complicated one. It's nice to be able to transform equations so that when plotted they form a straight line, but I can't think of any easy way to do this. Curve fitting can be a complicated business, but even Microsoft Excel can do basic curve fitting using an addon called the Solver.
Aug
14
comment Is it possible that electron and protons are created after a collision of matter and antimatter?
Google will find you lots of articles on the subject. For example this is a nice review.
Aug
14
comment What is the physical fundamentals of Pascal's law
Well no fluid is incompressible, and all fluids have a finite speed of sound. Both are a function of the bulk modulus, so are you really asking about the microsocopic origin of the bulk modulus? If so, that's a rather different question.
Aug
14
comment What would be gravity in one spatial dimension?
@Blazej: GR in dimensions other that 4 may or may not be physically irrelevant, but it's fun. What other reason for doing physics do we need?
Aug
14
comment What would be gravity in one spatial dimension?
GR isn't a physically relevant theory in 1+1D because the stress energy tensor must always be zero.
Aug
14
comment What would be gravity in one spatial dimension?
possible duplicate of General relativity (gravitation) in time and one spatial dimension
Aug
14
comment What is the physical fundamentals of Pascal's law
Why doesn't an ideal gas obey Pascal's principle? In an ideal gas (at equilibrium) the pressure is everywhere the same, so it seems to me that it obey's Pascal's principle. The restriction to incompressible fluids just means equilibrium is attained instantaneously because the speed of sound is infinite.
Aug
14
comment Reason for Uncertainty principle
possible duplicate of What is the physical meaning of commutators in quantum mechanics?
Aug
14
comment Is it possible that electron and protons are created after a collision of matter and antimatter?
@TamimAdDari: can you be more precise about what topic you want to know more about?
Aug
14
comment Can a Skydiver Land On a Large Slide and Survive?
@Schwern: as Chris says, it depends what you're trying to achieve. Using a circle converts vertical speed to horizontal speed with the minimum possible force on the skydiver. The skydiver can then slide along the runway (or whatever) shedding speed at whatever rate suits them. If the aim is to bring the skydiver to rest at the end of the slide then you're correct that the shape of the slide would be different. Actually that would be quite a complicated calculation.
Aug
13
comment When can we assume a body to behave like a black body?
I would have guessed that the tungsten filament is very close to a black body. However you may be losing some energy by conduction rather than radiation, and that could be why the filament isn't at as high a temperature as you expect.
Aug
13
comment Can a Skydiver Land On a Large Slide and Survive?
@MegaMark: I use Google Draw to do the diagrams. It's good for basic diagrams like this one, and it's free! :-)
Aug
13
comment Why does temperature have no uncertainity?
The temperature of a system is just a measure of its energy, so it's subject to the same uncertainty as measuring the energy.