John Rennie

44,258 reputation

12471

bio	website	ratsauce.co.uk
	location	Chester, United Kingdom
	age	52
visits	member for	2 years, 4 months
	seen	2 hours ago
stats	profile views	3,115

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.

	44,258 reputation	bio	website	ratsauce.co.uk	visits	member for	2 years, 4 months
12471 badges		location	Chester, United Kingdom		seen	2 hours ago

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May 6	answered	How much water is destroyed in photosynthesis, relative to the world's supply?
May 6	answered	Apparent non-aberration of gravity waves
May 5	revised	Does the current acceleration of universe imply that our universe is open? added 436 characters in body
May 4	answered	Geocentric Model in General Relativity
May 4	comment	What exactly is the microgravity field in orbit? Yes, isn't that the orbit the ISS moves in? My point is that assuming the ISS is normal to the vector joining it to the centre of the Earth then the distance from the ISS CM to the centre of the earth is smaller (by a few cm) than the distance from the front (i.e. leading edge) of the ISS to the centre of the Earth.
May 4	answered	Matter - Antimatter Reactory Practicality
May 4	comment	What exactly is the microgravity field in orbit? The ISS is a straight line not an arc of a great circle, so an object at the front (initially moving at the same speed as the ISS) is in a slightly higher orbit and therefore in a slightly elliptical orbit. Feed this into the vis-viva equation and you'll find it will start slowing down wrt the CM of the ISS. It will indeed move up (i.e. outwards) but also towards the back of the ISS. At least I think so; you have me wondering now.
May 4	comment	What exactly is the microgravity field in orbit? Assuming the ISS is straight, an obeject at the front will be slightly further away from the Earth than an object in the middle, so it will be moving more slowly and will tend to move from the front to the rear (as well as up and down). Does this count as acceleration parallel to the orbit?
May 4	comment	Effect of gravity at near-lightspeeds Incidentally, +1 for a very interesting question. I had to sit down and think about this for a while to get it clear in my own head.
May 4	answered	Effect of gravity at near-lightspeeds
May 4	answered	Proportion of energy compared to mass in universe
May 4	revised	Will a stone thrown in space move forever? added 237 characters in body
May 4	answered	Will a stone thrown in space move forever?
May 4	comment	How do you weigh a box on a scale whose limit is too low? @MartinBeckett: when I saw your comment I agreed and wasn't going to answer. Then it occurred to me that the centre of gravity of the package isn't known - it may not be uniform along it's length. Using a plank avoids this or at least reduces the error.
May 3	answered	How do you weigh a box on a scale whose limit is too low?
May 3	revised	Does the current acceleration of universe imply that our universe is open? edited body
May 3	comment	Does the current acceleration of universe imply that our universe is open? Oops, that should be $\Omega > 1$ of course
May 3	comment	what gives the vermiculite it's insultative properties Yes, if you buy vermiculite to use for insulation it will already have been exfoliated.
May 2	comment	Why do you get electric field of a light wave? @Manishearth: maybe we have different interpretations of what the OP is asking. His equation is a solution to the wave equation and in that solution $A$ is an arbitrary constant. I don't understand why we'd be worried about what value $A$ has.
May 2	comment	Does the current acceleration of universe imply that our universe is open? Hi Luboš, can you clarify that for me; maybe post an answer. I didn't think the FLRW metric with $\Omega < 1$ could have an accelerating phase because if $\Omega < 1$ the mass will always dominate over the cosmological constant. If the universe isn't FLRW then obviously all bets are off and it could do anything.