

Carrock
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Everything posted by Carrock
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Why would you need to cross an infinite amount of time? (Actually photons can cross infinite time according to very robust theory; are they irrelevant?) You seem to be saying that because we can't in any way reach the infinite past or future they cannot exist and duration must be finite. This is a philosophical belief; i.e. it's not science. When matter (or a person) crosses a black hole's event horizon it can never again reach the rest of the universe. Does that mean the rest of the universe no longer exists? Does the rest of the universe still exist for other matter?
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Time travellers only attended Stephen Hawking's party because they knew they could trust him to keep quiet and not destroy the delusion of causality.
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I have a dell with a 'mainly use on mains power' option in the bios where the battery presumably recharges more slowly in a life prolonging way. Worth having a look.
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Where can I buy a 20 Teraflop iphone?
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Maxwell's demon and the second law of thermodynamics
Carrock replied to Moreno's topic in Classical Physics
I agree with that as far as it goes. Conservation of energy and increasing entropy to heat death however are not always applicable in general relativity and quantum mechanics. --------------------------------------------------------- Statistically, very small regions undergo spontaneous reductions in entropy and there are also quantum fluctuations. Inflation posits that suitable very small low (classical) entropy fluctuations inflate into very large (> observable universe) low entropy volumes. Some versions of eternal inflation posit that this continues for finite but unlimited time. Other equally (im)plausible theories are available; a few have been falsified. -
Maxwell's demon and the second law of thermodynamics
Carrock replied to Moreno's topic in Classical Physics
The energy doesn't scale up. A football is a reasonable approximation to a giant gas molecule. It doesn't get moved around by random variations in air molecules' K.E. like a grain of pollen as observed in Brownian motion. There's lots of apparently plausible perpetual motion machines around; this is as far as I'm going with this one. -
Power from random walk of molecules in graphene sheets.
Carrock replied to DrP's topic in Science News
You could get even more power out with a heat engine running between ambient temp and the graphene which has been cooled by converting heat to work. I still haven't seen anything to suggest this isn't a second order perpetual motion machine. The original reference https://thibado.uark.edu/wp-content/uploads/sites/316/2017/06/PhysRevLett.117.126801.pdf is a little unclear but seems simply to claim that externally stressed graphene can produce useful power output. -
Maxwell's demon and the second law of thermodynamics
Carrock replied to Moreno's topic in Classical Physics
Only a rhetorical question. Consciousness as we know it depends on brains which inter alia are sophisticated heat engines producing a net increase of entropy. Actions by such creatures would also increase entropy at least as much as the reduction of entropy by their actions. If they are not limited like that, you may may as well say they run on magic or call them 'Maxwell's demons.' Such demons are an interesting concept, and if they existed could be used in a second order perpetual motion machine. You may find https://en.wikipedia.org/wiki/Maxwell's_demon interesting. -
Maxwell's demon and the second law of thermodynamics
Carrock replied to Moreno's topic in Classical Physics
What would these creatures live on? i.e. they presumably have to violate the second law themselves. -
Power from random walk of molecules in graphene sheets.
Carrock replied to DrP's topic in Science News
http://www.iflscience.com/technology/graphene-loophole-could-provide-clean-and-limitless-energy-in-the-future/ This appears to be a second order perpetual motion machine. Going from a promising design to a working model is always the problem. -
If the manufacturer got it right, overclocking is a sacrifice of reliability for speed. Getting higher spec components that provide the required speed is sometimes more cost effective. High reliability website hosts often underclock their processors and emphasize that in their advertising,
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The problem with added sugars is that they are consumed from a very young age and, like a (therapeutic) addictive drug, people, if unrestrained, get used to them and tend to take enough to damage health. A simpler answer might be to have a government health warning on products with added sugar. I'm not aware of any benefit from added sugar, except for morbidly underweight people or people exercising very hard. I stopped taking sugar in tea and coffee some years ago, and until I adjusted, was surprised at how many products I'd thought to be unsweetened tasted sweet due to added sugar. (xposted with Moreno) I stopped taking sugar
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No one on this thread has suggested 200µW of microwave radiation will do any harm (unless the authorities track down the jammer). One straw man. Actually an appeal to idiocy. In the example I gave, that would allow about 200µW through. A pretty basic narrowband receiver needs about 1pW input. And what is a Bd? Costs about 20 or 30 cents/square foot and is apparently about 11mm thick. I doubt from its attenuation graph that it's just a sheet of thin kitchen foil in a fancy wrapping so not like for like. I notice the advert has "approximately," without error limits or a guaranteed minimum. An experiment using less than a millionth of the required power at the rx, with an entirely predictable result. You might as well wave a wrist watch in front of your face to prove relativity wrong. So only one straw man.
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Straw man arguments.
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"Overlapping the joints + crimping them would work fine." As you don't mention it I assume you accept that 50dB attenuation figure I gave for commercial aluminum RF shielding foil which makes the above moot. "It may be instructive to wrap your mobile phone in foil carefully, then try to call it." A 20 mW or so signal from a low gain aerial on a tower attenuated to (far less than) 200nw (because of the distance) for an inefficient mobile phone aerial isn't equivalent to e.g. a 200µw signal near a radar dish trying to distinguish between that signal and a reflected signal from an ICBM 200 miles away. "then I think I emmit more than 200 µw of microwave radiation." Yes; broadband radiation. I thought it was clear I was talking about narrow band radiation, like with a mobile phone. If we compare like with like, the 200µW leakage from the 20W tx might have a bandwidth of 1KHz. If you emit 200 µw of radiation over the range 300 MHz to 300 GHz that would on average be around 10exp-17W in each 1KHz band.
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Note: Do not try this at home. Or at work. Or in a lab. Or in the ISS. Or... Defeat the safety interlock on your microwave oven and open the door. Hold a large sheet of cooking foil between your microwave oven and your eyes and switch on the oven. The eyes are not very sensitive to microwaves and respond very slowly. However after a few repeats your eyes will respond by developing cataracts. As it's not easy, if possible, to weld cooking foil, I assumed you meant wrap the source in cooking foil, which would leave gaps and enough leakage to detect the source at significant distance. Even without gaps, this was the best commercial shielding foil I could readily find: http://store.emfsolutions.ca/rf-shielding-foil/ You'd get a healthy 200microwatt signal from a 20watt shielded tx. As the OP appears to want a short range illegal jammer, with a 3m near field for 3cm waves no less, enough leakage for his jammer to be detected by Homeland Security or whatever would not be acceptable.
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These would shield in the sense of reducing microwave radiation to a (probably) safe level. Reducing the radiation to a level where it wouldn't be detectable by a nearby receiver would be a much bigger challenge. Based on experience, if you attenuate a 20W transmitter by a factor of 1000 down to 20mW omnidirectional (not trivial), it can cause interference with a dipole receiver system 20 miles away. Much further with a directional receiver aerial. Exactly.
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There was a quark bomb years ago in a TV serial called "Whoops, Apocalypse." I don't think it had a happy ending.
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Not so great for discarding a lit match...
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Barns are something I can finally congratulate Wikipedia on.
Carrock replied to studiot's topic in The Lounge
Lovely reference. Anther measure I always liked was for acoustic absorption: square feet of open window. -
No. If you want to know why I gave you a -1 rep read the thread.
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With the basic bolded errors I'm not going to bother with anything that might require a few seconds thought.
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It's mainly to avoid ambiguity or counting (fractional) numbers twice, since 1.000... = 0.999... etc I suppose 0.999... is generally used since unlike 1.000... it's clearer that writing 1 instead would not be useful in some contexts.
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Estimate the size of our universe
Carrock replied to Dream-Runner's topic in Astronomy and Cosmology
There is a simple problem with these assumptions. If information can travel faster than electromagnetic waves (photons), then time travel or acausality is possible. You're assuming gravitational waves take a 'shortcut' and arrive before any electromagnetic waves can possibly arrive i.e. they travel faster than light. Information is associated with gravitational waves.... -
How the Anonymity of the internet turns us into.... Well...
Carrock replied to DanTrentfield's topic in The Lounge
There are forums which 'force' members not to be anonymous. The only one I'm familiar with is the English Chess Forum which is much livelier than most chess forums. Addresses aren't published and I am not aware of any attempt to rob anyone. The lack of anonymity perhaps encouraged threats of legal action against the site owner by the English Chess Federation, but they seem to have given up in recent years.