Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Pseudoscience-is-malarkey on 13/12/2020 15:44:40
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Our universe is full of limitations. There's a limit to how fast something can get, how much gravity a non-black hole object can have, etc.
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Nothing can get colder than 0K - or indeed even approach absolute zero indefinitely.
If all the mass of the universe were invested in the energy of one electron it would have the highest achievable temperature.
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Nothing can get colder than 0K - or indeed even approach absolute zero indefinitely.
If all the mass of the universe were invested in the energy of one electron
...then there would be nothing to compare the election to. You wouldn't know it was moving. It would have zero energy from it's point of view, and there would be no other point of view.
If you took all the energy from the universe - apart from a few particles- then... you would have cooled those particles to absolute zero- which is impossible.
Temperature isn't a well defined concept if you don't have an ensemble of particles to consider.
If you got round all that- somehow- then you would still do better by giving all the energy available to a few neutrinos.
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At the point where there were just two electrons left, each would have a definable kinetic energy. Now dematerialise one of them and impart all its energy to the other. It will experience acceleration and will therefore know it is the lastest and fastest!
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At the point where there were just two electrons left, each would have a definable kinetic energy. Now dematerialise one of them and impart all its energy to the other. It will experience acceleration and will therefore know it is the lastest and fastest!
Or it may realised that the magnitude of the acceleration could have been the same if it had slowed down to a stop.
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Nothing can get colder than 0K - or indeed even approach absolute zero indefinitely.
What is absolute zero is it just a concept of vibration over time?
Surely the upper limit is light, no mass except relative mass, no way of higher speed, if light has a speed given that it is not entirely understood.
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What is absolute zero is it just a concept of vibration over time?
It's a temperature.
Specifically, it's -273.15C
On the other hand, "just a concept of vibration over time" is meaningless gibberish.
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Carnot showed that the maximum efficiency of a theoretical heat engine (i.e. one that extracts heat from a hot source and delivers it to a cold source to produce mechanical work) is
η = 1 - Thot/Tcold
so for any finite temperatures, η ≤ 1 and there can only be one temperature Tcold for which η = 1, which defines absolute zero.
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That you can't get to zero kelvin is explained by the Heisenberg Uncertainty Principle. It just states that there always will be a uncertainty to the momentum which means that you can't get anything absolutely 'still', no matter how cold you try to make it. When it comes to how hot something can become I don't know any definition of it?
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That you can't get to zero kelvin is explained by the Heisenberg Uncertainty Principle. It just states that there always will be a uncertainty to the momentum which means that you can't get anything absolutely 'still', no matter how cold you try to make it. When it comes to how hot something can become I don't know any definition of it?
Not quite. The impossibility of reaching absolute zero can be established by purely classical thermodynamics.
The added complication from QM is this: even if a system were to be at absolute zero, it still has some non-zero amount of kinetic energy, the so-called "zero point energy." This is the minimum amount of internal energy the system can attain, so there is zero extractable energy, just not zero energy.
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If the "thing" still has to be recognizable as the "same thing" it started as, this will be highly thing-dependent. (ie there is a limit to how hot an ice sculpture can get, while still being an ice sculpture, and that is very different from the temperature at which protons cease being protons...
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Well, depends on definitions I think? HUP states that there is a uncertainty. It doesn't state that we have a way to measure it.
" Practically, the work needed to remove heat from a gas increases the colder you get, and an infinite amount of work would be needed to cool something to absolute zero. In quantum terms, you can blame Heisenberg’s uncertainty principle, which says the more precisely we know a particle’s speed, the less we know about its position, and vice versa. If you know your atoms are inside your experiment, there must be some uncertainty in their momentum keeping them above absolute zero – unless your experiment is the size of the whole universe. "
It's funny, in some ways it connects to light, doesn't it? The way we say that you will need a 'infinite energy' to reach 'c' for any matter related concept, and here the definition becomes that you need a 'infinite amount of work' to reach 0 K.
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You could argue that you don't need HUP but I wouldn't agree. Zero point energy is best exemplified by the Casimir effect
theorized 1948 but HUP, presented 1927, should be what it builds on, as a guess. I could look it up but I'm too tired for the moment.
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The indeterminacy principle ("uncertainty" is a serious misunderstanding) does not predict or calculate absolute zero. It is an entirely classical thermodynamic concept.
What QM does predict is that helium, uniquely, would remain liquid at 0K and atmospheric pressure.
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In quantum terms, you can blame Heisenberg’s uncertainty principle,
Not really.
If ( its a big "if") you cooled a crystal to absolute zero there wouldn't be a problem with the uncertainty principle because, even at 0K the atoms would still be vibrating. If memory serves, the energy is half h f
Motion doesn't necessarily stop at 0K
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That you can't get to zero kelvin is explained by the Heisenberg Uncertainty Principle. It just states that there always will be a uncertainty to the momentum which means that you can't get anything absolutely 'still', no matter how cold you try to make it. When it comes to how hot something can become I don't know any definition of it?
As stated earlier surely temperature is a measurement of particle movement over time, as such to achieve zero K, the said matter would have to have no energy ever in the existence of time, thus would have to have avoided the big bang. Idon't believe temperature is descrete and if it was you would need something of zero K to draw energy from other matter. If anything ever was zero K would it exist?
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Whilst Heisenberg is often represented as the impossibility of knowing both position and momentum with absolute precision, that's a derivation from billiard-ball mechanics applied to bouncing a photon off a moving electron, which clearly cannot represent reality.
Consider a hydrogen atom. If the electron really is a moving particle it must be moving in some sort of orbit, because the atom has a finite size considerably larger than a proton. But an orbiting electron emits energy so it will spiral into the nucleus and disappear. Therefore the electron is not actually a moving particle and the classical model is false, even though it gives the right value for h.
Hence my preference for "indeterminacy" rather than uncertainty. Matter behaves as though Δp.Δx ≥ h.
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BC that one you have to link. The way I understand it you can't reach 0 K. Are you suggesting there exist a possibility of it? Whether you want to call indeterminacy or uncertainty seems more of a personal taste to me Alan, I grew up calling it uncertainty and I will probably stay there :)
I don't know Petro, If we go by BC you seem to be able to, at least theoretically, describe a state in where you can reach 0 K but where you still can't define the momentum, or lack of. What that implies would then be a state where you have to look for something complex, as in a imaginary number combined with a real, describing it. As it seems to me. That's why I want that link. Intuitively I would say that something should break down and change if you can reach zero Kelvin. But I don't know.
http://www.quantumphysicslady.org/glossary/heisenberg-uncertainty-principle-hup/
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It depends on how you define heat possibly, and what you consider to be matter. Matter as waves or as something tangible that you can touch. If everything would be waves (matterwaves) then what HUP states should be that those waves aren't there, until we 'touch' them. And heat can be described through waves too. The absence of a wave jiggling / propagating would then be a state of absolute zero as I use to think of it, but if BC is correct, which he probably is :) you either can have a state of no jiggling / propagation still not able to prove it to be still, or you might be able to imagine that it becomes a doorway to another state.
Take a look at Jim Al-Khalili description in the link to see what I mean by HUP 'stating' that you need to 'touch' it. HUP becomes a very general application on almost everything it seems. Even waves doesn't come close enough, does it? Alan wants to call it indeterminacy and that seems correct in this case. A uncertainty of something implies that it exist, we just can't 'pinpoint' it until we touch it, where indeterminacy could be read as implying that it doesn't even need to be there at all. Which, to me then, connects to the idea of decoherence.
and what I mean by that is that you might be able to see the existence of something, once we 'pinpointed' it, as a result of a whole universe interacting. Or if you like the laws and properties existing defining it in your 'touch'. See why I find 'New Theories' a comfortable place?
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As stated earlier surely temperature is a measurement of particle movement over time, as such to achieve zero K, the said matter would have to have no energy ever in the existence of time,
Only to the same extent that an ice cube always had to be below 0C since the start of time.
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Are you suggesting there exist a possibility of it?
No
I'm pointing out that, even at very low temperatures the vibrational motion does not stop.
You can cool things down to temperatures like that- where you would expect few, if any molecules to be vibrating. And they don't stop. Low temperature heat capacities are another demonstration of the quantisation of energy.
Similarly, there's nothing in the uncertainty principle to stop you cooling a single molecule in a test tube down (The physicists' beloved ' particle in a box' model) to "zero".
The molecule would stop moving, but you wouldn't know where it was.
Translational energy doesn't have a "zero point energy" in the way that a vibration does.
Much as I love the Hitchhiker's guide to the galaxy, I'm not generally going to follow Alan's lead of using it as a source of scientific terminology.
" It is said, by the Guide, that such generators were often used to break the ice at parties by making all the molecules in the hostess's undergarments leap simultaneously one foot to the left, in accordance with the theory of indeterminacy."
https://hitchhikers.fandom.com/wiki/Infinite_Improbability_Drive
I will stick to calling things by the names that will ensure that they are recognised.
I agree the idea is badly understood but I'm not sure the name is the big sticking point.
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It was Heisenberg's word.
The problem as I see it is that the principle is usually taught via the classical photon/electron model, which leads to the absurd collapsing atom. I think the world has now grown up enough that we could teach physics from quantum mechanics and relativity, pointing out that as we scale up from atoms and down from near-c velocities, we can make classical approximations, using continuum mathematics and invariant masses for most (but by no means all) engineering purposes.
The result would be a much clearer view of the current state of knowledge. But it requires, inter alia, abandoning the anthropic "uncertainty" business (and all the crap that goes with conscious observers...) and accepting that there is an inherent indeterminacy at the root of the universe.
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It was Heisenberg's word.
Really?
That's odd. I thought his work was in German.
http://www.psiquadrat.de/downloads/heisenberg1925.pdf
I think the world has now grown up enough that we could teach physics from quantum mechanics and relativity, pointing out that as we scale up from atoms and down from near-c velocities, we can make classical approximations, using continuum mathematics and invariant masses for most (but by no means all) engineering purposes.
You propose that we teach physics by starting from something we don't understand or experience and working towards something we do.
I invite you to discuss that ordering with any teachers you know.
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I propose to start with something we have known for 100 years, and show how it explains what we see every day. It would need some revision of adjoining subjects, so that the good bits of applied maths (vectors, calculus...) and the classical physics experiments become engineering.
One of my sons is a physics teacher. Unfortunately he is constrained by a curriculum, apparently written by people who consider x-rays "modern". As an Oxford alumnus, you will know that "modern" means "post-Roman" to the cognoscenti. I prefer to call early 20th century physics "knowledge".
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I propose to start with something we have known for 100 years
You and I probably have known if for a hundred yeas or so (between us), but we aren't schoolkids.
But trying to teach physics staring with Einstein (F might equal MA) and working back to Newton (F=MA) is just going to confuse the students.
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It's much easier to paint on a blank canvas.
I'd start with Einstein's discussions about passing trains. How do we know we are moving? We don't!
Then I'd talk about thunderstorms or fireworks: we see the flash long before we hear the bang, and the further away, the bigger the difference, so information travels at different speeds depending on the medium of transmission.
So what do we know about events a long way away? Let's think about history. Time was that information couldn't travel faster than a horse or a ship (how do you organise the Battle of Hastings? One army is loading ships 50 miles away, the other is fighting at Stamford - how do they get to meet?) but even with radio waves (how fast do they travel?) we only know what happened in New Zealand about 0.15 seconds ago.
....and so on. Pretty soon we'll be asking about time dilation.
Then some bright kid will point out that you know when the train starts moving because you can feel the shove and old ladies start falling over, and away we go again....
As soon as you introduce atomic theory you can talk about electrostatics and ask the question (that turns up depressingly often in these boards) why the electron doesn't just stick to the proton like the balloon sticks to the ceiling. You can muck about with cars and stopwatches and investigate the experimental limits of Δv and Δx then skip to Heisenberg's hypothesis that there is a fundamental limit , and away you go with a discussion of indeterminacy that doesn't involve experimental error but does predict the diameter of an atom.
Now here's a question from an obnoxious schoolkid. How do we know that c is a limit? I can derive Maxwell's equations by a bit of handwaving with a magnet, but why isn't there anything faster, Sir?
Sir Lawrence Bragg (my hero) used to say that you can't claim to understand anything unless you can explain it to a 7-year-old. Any takers for this one?
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Then some bright kid will point out that you know when the train starts moving because youi cann feel the shove
And that's when Newtonian physics comes in ...
But trying to teach physics staring with Einstein (F might equal MA) and working back to Newton (F=MA) is just going to confuse the students.
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It's much easier to paint on a blank canvas.
Exactly; you need the canvas first.
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Then some bright kid will point out that you know when the train starts moving because youi cann feel the shove
And that's when Newtonian physics comes in ...
Big problem. Newtonian physics ends up with the remarkable finding that gravitational mass = inertial mass, but doesn't explain why.
All you need to move on with the relativity discussion is to note that we can detect acceleration but not constant velocity, which is what the kid has just told you. That finding can take you in both directions but whilst the Einsteinian formalism degenerates to Newtonian if v<<c, the reverse is not the case, which is why relativity had such a hard time getting accepted until proven by experiment.
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All you need to move on with the relativity discussion is to note that we can detect acceleration but not constant velocity,
What we actually "detect" is a force. If the car accelerates forwards, I get "pushed" back into my seat and (per Newton) I feel the seat push back on me.
At constant velocity A = 0 and thus F=0
So, Newtonian physics explains that just fine.
But you can't explain how we "detect" acceleration without using Newtonian physics.
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Newtonian physics doesn't explain F = ma, but states it either as a definition of F, an observed fact, or a consequence of F = d(mv)/dt, all of which is true for small v but by no means explained.
All we need to get the relativistic discussion going is the observation that old people fall over when the bus starts or stops, but seem quite capable of standing up when it's cruising at 50 mph. Today's bright kids might wonder why they lock the toilet doors when a plane enters the approach pattern: again Newton calculates the pee arc, but doesn't explain it, or extend it to explain how GPS works.
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Newton calculates the pee arc, but doesn't explain it, or extend it to explain how GPS works.
That would be relevant if, and only if, I was saying that we shouldn't teach relativity.
You seem to be planning to start with why the GPS clocks are set to tick at the wrong rate (here on Earth) and go on from that to explain how a go-cart rolls down a hill.
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I have no idea why a go-cart rolls down a hill. Nobody knows why gravity only sucks, or why minertia = mgravitation, even though we can calculate how fast it would go on Mars.
Our ancestors knew the sun would rise in the same place every 365.25 days and the spring tide came with a new or full moon, but had no idea why. The observation and empirical calculation made farming and sailing a lot easier, and Newtonian physics doesn't take us much further.
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Nobody knows why gravity only sucks, or why minertia = mgravitation,
Nor do I. Nor did Newton, Nor did Einstein.
Newtonian physics ends up with the remarkable finding that gravitational mass = inertial mass, but doesn't explain why.
So... it's the same as relativistic physics.
Since they are the same (except one is more complicated) why not teach the simpler one first?
If you were building a house, would you try to put the roof on first?
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Not a house, but I often erect a small marquee for jazz concerts and always start with the roof.
The problem is that if you teach, say, the Bohr atom, you then have to spend hours explaining why it isn't a good model when people make entirely logical but clearly wrong deductions from it. We don't teach humors and miasms, creationism, divination from chicken entrails, or compression waves in the aether (which still turned up in radio engineering texts in the 1930s) so why not proper physics?
If you were brought up on miasms, you might find virology hard to comprehend, but it's part of the A level syllabus because it's what we (except politicians) know to be true.
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We don't teach humors and miasms, creationism, divination from chicken entrails, or compression waves in the aether
False equivalent
None of those is a simplification of the real world which applies in the low velocity (or any analogous) situation, is it?
Why did you bring it up?
but I often erect a small marquee for jazz concerts and always start with the roof.
And then, presumably, you go hunting and foraging for something to hold it up.
Or are there pre arranged poles?
Because, if there are, you don't raise the roof until you have the poles.
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They are all previously accepted models of reality that don't stand up to rigorous analysis.
Since the real world seems to behave according to relativity and quantum mechanics, with as much rigor as we can apply, surely they should be the foundation on which we base our models?