961

Technology / Re: Negate the expansion of freezing water using small, compressible balls

« on: 12/11/2015 22:31:52 »

We do this to absorb the thermal expansion of oil in x-ray tube assemblies. The "absorber" is a small rubber bellows or ball filled with nitrogen that compresses as the oil expands.

This might work in principle with freezing water but you might need several balls as the water will freeze from the top downwards and thus trap a floating ball.

Alternatively put the water in a flexible bag inside a metal or glass bottle.

962

Physiology & Medicine / Re: What makes us human?

« on: 12/11/2015 13:50:03 »

We are very little different from any other mammal. There is a presumption of limited interfertility, which partly defines a species (though some politicians are alleged to have tried mating with suidae, presumably to improve the manners and intellect of the political class) but the more obvious characteristic is the desire to record things that are too trivial to remember: in this, we seem to be unique. 

963

Physics, Astronomy & Cosmology / Re: Is the Copenhagen Interpretation correct interpretation of quantum mechanics?

« on: 12/11/2015 09:40:42 »

Try full screen and freeze frame. You will see that the particle never touches the divider. Indeed it can't, because it is being carried by the wave, not the other way around, and if the wave amplitude was zero between the particle and the divider, the particle would fall into the "soup".

It's very pretty, but it's just mesoscopic fluid dynamics and nothing to do with quantum physics.

964

Physics, Astronomy & Cosmology / Re: Is the Copenhagen Interpretation correct interpretation of quantum mechanics?

« on: 08/11/2015 18:30:12 »

The following image shows the interference pattern build up over time for electons.

The key here is "build up over time". A single electron can't provide an interference pattern because, unlike a wave, it is indivisible. What we actually detect, whether electrons or photons, is individual particles hitting the detector with a spatial distribution that looks like wave interference. 

965

Physics, Astronomy & Cosmology / Re: Why don't an atom's electrons fall into the nucleus and stick to the protons?

« on: 08/11/2015 13:41:09 »

A neat reference- particularly as it supports my preferred use of "indeterminacy" for Heisenberg's principle.

I still think it better to start from the observation that atoms have a finite diameter, therefore you can't assume that classical electrostatics will model it.

966

Physics, Astronomy & Cosmology / Re: Is the Copenhagen Interpretation correct interpretation of quantum mechanics?

« on: 07/11/2015 01:00:29 »

According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured,

No. That is a misleading formulation. It is true that we don't know anything about a particle until it interacts with another particle. The fact that I don't know whether you are wearing a hat until I see you, has nothing to do with whether you are or are not wearng a hat: I can't draw an accurate picture of you until we have met, but that meeting doesn't determine your appearance because you must have put the hat on before we met.

and quantum mechanics can only predict the probabilities that measurements will produce certain results.

Yes

The act of measurement affects the system,

Yes

causing the set of probabilities to reduce to only one of the possible values immediately after the measurement. This feature is known as wavefunction collapse.

No. What happened is what you measured. Waveform collapse is a mathematical model of what happens.

967

Physics, Astronomy & Cosmology / Re: What is the largest possible rest mass of the photon?

« on: 07/11/2015 00:55:26 »

Science is the recursive application of the algorithm "observe, hypothesise, test". Philosophy is something else. It usually involves an incomplete observation, a wholly irrelevant hypothesis, and an excuse to do something bizarre or evil. Testing and recursive refinement are beneath the lofty intellect of a philosopher, which is why they tend to flock with those other arrogant purveyors of ignornace, priests and politicians. If you allow philosophy to infect science, you end up with such perversions as Nazi science, Lysenkoism, Maoism, ruin and starvation. Evolution is a scientific observation, creationism is a philosophy. There is no scientific justification for beheading infidels, but a powerful philosophy can sanctify it. 

The overweening arrogance of philosophers is apparent from Evan's posting. As is the fatuous nature of philosophy

Photon, Elementary particle, Particle physics, Physics, Natural science, Science, Knowledge, Awareness, Consciousness, Quality (philosophy), Philosophy.

It all makes sense until you get to "consciousness", a term which is never defined by its users: everything thereafter appears to derive its place in the thread, from a meaningless word. Philosophically, a photon must be a wave or a particle, so the properties of electromagnetic radiation depend on some notion of duality and observer-dependence...what utter rubbish! We scientists use the term photon to denote the cause of a number of linked phenomena: it doesn't "have to be" anything other than itself, and we admit that we don't have a unique mathematical description of all its properties. That is a far more mature, and far less arrogant and athropocentric way of looking at the universe.   

968

General Science / Re: Does UVC light sterilize only the surface?

« on: 06/11/2015 08:44:24 »

UVC is primarily a surface sterilant, though it can be used to sterilise thin layers of circulating water.

We use heavy cotton overalls for protection against UV therapy sources: penetration through a lab coat or jeans is almost negligible.  Since any pathogens in a pillow will be distributed throughout the filling (where it's warm and moist) you really need steam, bleach, gas or gamma radiation, to have any useful effect.

Any sterilant (including UVC) will be extremely dangerous if it is effective - you are made of the same stuff as bacteria, but they are a lot tougher. Don't try any of this at home!

969

Physics, Astronomy & Cosmology / Re: Can a photon be length contracted?

« on: 04/11/2015 22:31:04 »

If an object has no existence at rest, it cannot contract from its rest length.

970

Chemistry / Re: Does burning candles improve air quality?

« on: 30/10/2015 16:18:56 »

No. High quality air contains only oxygen and nitrogen with a hint of water and CO2. Burning anything increases  CO2, decreases O2, and adds soot and volatile materials to the mix, none of which is good for you.

"Cooks' candles" absorb strong odours but you are just substituting one chemical  pong for another.

971

Physics, Astronomy & Cosmology / Re: What is the largest possible rest mass of the photon?

« on: 30/10/2015 09:53:09 »

The lowest possible frequency is any number greater than zero. However as Evan says, the lowest detectable frequency depends on the length of your antenna and your patience. As the earth's magnetic field drifts and reverses every billion years or so, there's at least one known photon out there with a lower frequency than sunspots, but you'd have a tough job to find it.

972

Physics, Astronomy & Cosmology / Re: Is there one fundamental energy?

« on: 27/10/2015 08:21:21 »

No.

Energy is a scalar quantity that we have invented, and we observe to be conserved.

973

Physics, Astronomy & Cosmology / Re: Could you become a God by traveling at the speed of light?

« on: 26/10/2015 21:32:47 »

 Could you become a God by traveling at the speed of light?

No. Or possibly Yes. But since you can't travel at the speed of light, don't waste too much time on the subject.

974

Geology, Palaeontology & Archaeology / Re: When during human evolution did the first scientist appear?

« on: 25/10/2015 20:52:58 »

No. Evolution is about what the cell did next, not how it came into existence in the first place.

975

Geology, Palaeontology & Archaeology / Re: When during human evolution did the first scientist appear?

« on: 22/10/2015 23:59:10 »

In 1983 I watched a gorilla at Chessington Zoo discover the principle of universal gravitation. He had two apples, one considerably larger than the other, one in each hand. He dropped them and noticed that they hit the ground at the same time.  He repeated the test, twice, then changed hands and did it again. Perfect null experimental technique: observe, repeat, change one parameter.

On the presumption that gorillas don't read books or have much of an oral tradition of scientific knowledge, this chap discovered, by the application of best scientific practice and in the space of five minutes, what took humans several million years and and a fair bit of bloodshed. Indeed there is no historical evidence that Galileo actually did his  "leaning tower" experiment, and if you read some of the bizarre submissions to this forum, it's quite clear that very few humans appreciate even the simplest principles of scientific investigation. Of course the gorilla didn't have to shake off centuries of superstition and the threat of excommunication, which gave him a huge advantage over Bruno et al.

Having seen birds, rats and chimpanzees deduce causal relationships from observation, and having marvelled at the gullibility of humans (including verbatim acceptance of garbage like Genesis) for many years, I fear that scientific thought in homo sapiens is something of a rarity compared with other species. Worse: when it appears, the herd generally tries to stamp it out, always preferring consensus and superstition to the demonstrable truth - unlike blue tits.

 

976

Chemistry / Re: Could a solar powered cooling system be used to collect water from the air?

« on: 16/10/2015 17:41:30 »

Assume a coefficient of performance of about 2. Your 150W refrigerator can therefore shift about 300W of heat. Condensing 1 gram of water requires about 2300 joules of heat to be extracted, so you can condense 300/2300 =  0.13 gram per second. If the water content of air is about 5% you need to pass 20 x 0.13 = 2.6 gram of air per second over your condenser - about 2 liters/second. You can probably achieve this with a 2W fan, which won't impose a significant load on your power supply.

977

Physiology & Medicine / Re: Urinating on the moon.

« on: 15/10/2015 22:58:10 »

A pee tube is built into any pressure suit intended for long-term wear. Short-term you use a nappy (diaper).

Glider pilots suffer from cold: a flight of more than 3 hours becomes a test of bladder control and moral fibre as much as airmanship. So some gliders have a venturi waste tube attached to a rubber cup (known in less PC days as the "Polish microphone" - well, it was invented in Poland) but a fighter test pilot, accustomed to having proper personal plumbing in his office suit, attached himself to a glider venturi with a transparent polythene bag. The other thing glider pilots suffer is sunburn. The experiment was well publicised in the 1970s and I don't think has been repeated.

978

New Theories / Re: Newton's 3rd Law + Logic = Genesis?

« on: 15/10/2015 00:51:47 »

The universe contains stuff, which we observe behaves in certain ways, called physical laws.

Now consider that there may have been a time when the stuff did not exist. There being no stuff to behave, there were no observables that could be set down as physical laws. The laws are a summary of the existence and behaviour of stuff: they are descriptive, not prescriptive, which is why it is no big deal if classical mechanics doesn't describe what goes on inside an atom or a black hole, or at very high relative speeds.

So if the laws of physics applied before stuff, to what did they apply? You will have to postulate protostuff which, having the same physical properties as stuff, must therefore be stuff.

Thus the postulate that the laws of physics applied before the creation of the universe is inconsistent with the notion of a point of creation.

979

General Science / Re: How would you operationalize Authority?

« on: 12/10/2015 16:09:37 »

"Command authority" is the authority leaders have over soldiers by virtue of rank or assignment

which, though easy to assess, I suspect isn't really what you mean. However we do use the term as a variable attribute when assessing civilians for roles of leadership or responsibility.  You could usefully talk to personnel officers in large companies, examiners for mariners or aviators (especially traffic controllers in those media) or police instructors.   

980

Marine Science / Is space or sea exploration the better use of our resources?

« on: 20/08/2015 22:35:14 »

Considering how much tax revenue is wasted on wars (on drugs, terror, cancer, or just rearranging the rubble in Afghanistan) banks, and friends of politicians, any such discussion simply diverts critical attention from high level corruption. Whilst the peasants argue over the distribution of crumbs, those we elect to take our money feast on the real meat.