1

New Theories / Re: what is temperature?

« on: Today at 00:18:15 »

 As it happens I don't think there is a good theoretical model for porridge.  As such Goldilocks probably can't determine the temperature of her porridge on the modern (post 2019) kelvin scale.   That temperature is simply "unknown" or "undetermined" at this time.

Things aren't quite that bad. She may not find it easy to calculate, but it's very easy to measure with a thermometer calibrated in K.

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New Theories / Re: An essay in futility, too long to read :)

« on: Today at 00:03:14 »

I don't know. The over population today, if we set a limit of one billion people as a sustainable goal, means that out of eight people existing today only one can remain, let's say 2050. But then we have projections as " World population projected to reach 9.8 billion in 2050, and 11.2 billion in 2100 "

But if we stop making babies tomorrow, the human population will decline to zero by 2122. So we have a choice, including the option to reduce the population to an indefinitely sustainable level, by doing nothing.

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New Theories / Re: An essay in futility, too long to read :)

« on: Yesterday at 23:58:09 »

Well, Alan, you didn't answer my question.Do green house emissions matter?

Greenhouse gases certainly matter. Water is the principal variable that determines the temperature of the earth's surface (even IPCC says so!). Carbon dioxide has some effect but above 200 ppm its absorption spectrum is almost certainly saturated. They are closely coupled, as the historical record shows: an increase in temperature generates an increase in atmospheric CO2 (see the Keeling curve seasonal fluctuations), which is counter to the rate of anthropogenic emission (we burn less fuel in summer).

Most important: climate change is beyond human control, so it is imperative that we mitigate its impact on human society.

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: Yesterday at 23:49:23 »

If the thermopile is heating up, then it is doing so by gaining energy from the fly or whatever.
And that means the fly is cooling down.
So you are not measuring the fly, you are cooling it.
If the thermopile is cooling then you are warming the fly.

You are beginning to see the picture.
Now what do you deduce if dV/dt = 0?

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: Yesterday at 16:21:55 »

You look at the thermopile voltage and rate of change.

V α T_thermopile

dV/dt α ΔT (thermopile - fly)

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Just Chat! / Re: Initials grammar...

« on: Yesterday at 16:11:37 »

Passionate? Poignant? Debate?  Every major publication has a style manual. Most scientific publications use a version of the Library of Congress indexing standard, and the UK civil service (including Hansard) generally refers to The Times as a working standard.

You might however like to twist your own knickers over your own "W C Fields' "  or "W C Fields's".

Many classic 12-bar blues were written by W C Handy. Always a fallback to warm up a new band, my old bandleader used to say "When the band's playing like sh1t,  it's good to have a WC handy."

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: Yesterday at 16:05:25 »

Nowadays, yes. The question was put to undergraduates in 1963. And it still doesn't answer HY's problem of not extracting energy from the object.

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New Theories / Re: An essay in futility, too long to read :)

« on: Yesterday at 16:02:52 »

You can build a lot of logic on a false premise. Problems arise when your action plan fails to deliver because your premise was irrelevant to or insufficient for the problem. Have another look at #33429 above.

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New Theories / Re: An essay in futility, too long to read :)

« on: Yesterday at 15:40:08 »

A simple definition would be that if we get rid of this overpopulation, everything will turn back to normal.

Obviously not, because there is no normal. The European climate of the 1960s was desirable but Bihar and Biafra suffered famines.

A smaller human population could tolerate a less favorable climate, and even enjoy the present climate more. That's Plan A - resilience.

Plan B must involve the orderly elimination of fossil fuels, obviously because of their finite supply (i.e. sustainablity), but more urgently because they make democracies dependent on dictatorships.

Even if the climate were to play nicely, we can't sustain a desirable standard of living for the present population without fossil fuels, so we need to implement both plans.

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New Theories / Re: An essay in futility, too long to read :)

« on: Yesterday at 15:37:54 »

What have I denied? The facts are undisputed, but the consensus mechanism behind them doesn't make sense. So I'm skeptical about the consensus.

That's how science progresses. Nobody ever denied that the sun rises every morning, but the skeptics suggested that maybe the earth rotated, not the consensus sun. Who was right? 

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: Yesterday at 15:23:25 »

How do you detect it if energy is not leaving the system?

When you don't detect it coming or going, it isn't transferring. Therefore the subject and the reference must be at the same temperature.

A clever way to do this (at least in principle)  is to put your sample and a small thermopile at the foci of two spherical mirrors facing one another. You heat the thermopile by passing a current through it, and measure its temperature by measuring the voltage across it when you switch off the heating current. If the sample and the thermopile are at the same temperature its voltage won't change with time immediately after switchoff.  But as I remarked elsewhere, practical heat experiments are very difficult to do!  The experiment was originally devised in response to an interview question:how would you measure the temperature of a fly?

12

Just Chat! / Re: A Short puzzle with dogs.

« on: Yesterday at 09:40:34 »

I've always wondered whether "proper" mathematicians allowed the use of obvious symmetry and reflection as tools in a formal proof. I was so inspired in my youth by Kasner and Newman's "Mathematics and the Imagination" that I married the only girl I ever met who shared that enthusiasm (both, it turned out, recommended by our electrical engineer fathers). Like a good novel, it began with a surprise - the use of obvious symmetry to simplify a classic proof.

The dog and river problem actually has a practical application in navigation. If you are sailing or flying to a visible destination with an unknown cross wind or tide, simply aiming directly at the target will take you on a spiral pursuit curve, arriving pointing directly into wind. The trick is to maintain your original compass heading for half the distance, then turn through four times the difference between that and the new bearing. It's oddly counterintuitive but definitely optimal.

13

New Theories / Re: An essay in futility, too long to read :)

« on: Yesterday at 09:21:38 »

that deniers and skeptics will use to once again 'prove' that we have nothing to worry about.

As a skeptic, I can demonstrate that we have plenty to worry about - assuming that the collapse of human civilisation is worth worrying about - and tinkering with carbon dioxide emissions isn't going to solve the problem or even have a significant impact on it. Indeed in the short term it may even increase inequality and political tension.

All living things destroy their environment. It's the essence of life processes. The trick is to find another living thing that can repair the damage, and to adjust the populations of both to achieve a sustainable equilibrium. Humans are uniquely able to  do this prospectively, and still too stupid to do it.

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: Yesterday at 09:11:00 »

Depends on what constitutes temperature? Is it on atomic level or subatomic level, is the temperature considered to be on the substance in question or the measuring device. For example how could you ever measure temperature without the substance in question loosing some energy.

Temperature is the mean internal kinetic energy of a mesoscopic body. It has no meaning for an individual particle.

You can in principle measure temperature without net heat loss by detecting the heat flow between the subject body at T_S and a reference at T_R. when there is no flow, T_S = T_R.

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Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 14/05/2022 16:14:02 »

But temperature is not defined for an individual particle, only for a bounded ensemble.

If you want to be picky (and I'm sure some of our correspondents do) you could say that a flowing liquid or gas doesn't have a defined temperature because there will be a velocity gradient therefore a significant variance in local internal kinetic energy. Hence my preference for "stuff" rather than "thing" if the ensemble isn't bounded.

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Physics, Astronomy & Cosmology / Re: Is there a net heat exchange between water and ice at 0 degree C?

« on: 14/05/2022 16:12:07 »

Convection will make temperature of the bath more uniform around 0C.

No. Convection requires a temperature gradient.

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Physics, Astronomy & Cosmology / Re: Is there a net heat exchange between water and ice at 0 degree C?

« on: 14/05/2022 16:11:15 »

I'm beginning to think you enjoy the feeling of being confused.  You now seem to not even know what a definition is.  I don't get you at all.

The object of philosophy is to tell people that they don't (or even can't) understand the obvious. I think HY is an undercover philosopher.

18

Just Chat! / Re: A Short puzzle with dogs.

« on: 14/05/2022 00:14:55 »

Each dog starts running towards the dog immediately anti-clockwise to it.

Apologies for not addressing the problem mathematically, but the experimental scientist knows that whilst small children follow a pursuit curve, dogs are actually better hunters and tend to run in a straight line towards a predicted intercept. Eventually, some children learn the trick and turn into good cricketers or footballers. David Beckham's exceptional ability as a midfielder was being able to make long passes to an intercept so that wingers and strikers could run on to the ball at full speed in a straight line.

Late edit: it's also the art of a fighter controller!

19

New Theories / Re: what is temperature?

« on: 13/05/2022 23:58:56 »

 Also "mesoscopic"?  Did you really mean middle-sized? 

somewhere between microscopic (where quantum effects add significant noise to your measurement) and astronomical (where simultaneity cannot be assumed). Usually refers to manageable things like bricks and cows. 

 

  Temperature is telling you about the average kinetic energy of a particle among a myriad of otherwise identical particles

They don't need to be identical. Porridge is inhomogeneous, but Goldilocks was able to measure its temperature. Temperature is the mean kinetic energy of all the particles in a sample.

20

Physics, Astronomy & Cosmology / Re: Is there a limit to how hot things can get?

« on: 13/05/2022 23:48:02 »

Strictly speaking, if you increase the temperature of a "thing" sufficiently, it ceases to be a thing and turns into a liquid (having no defined shape it's a "stuff" rather than a "thing") then a gas, then atoms and finally plasma. The limiting temperature of plasma is the point at which all the energy of the universe, minus the mass of the thing, is invested in the ex-thing plasma.