The Last Conformist
Irresistibly Attractive
That would imply stating the answer with an unusal degree of eloquence, I guess ...
Science Quiz
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betazed
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Before I answer the question let me spend some time on why I think the question makes sense. Many of you would think (and rightly so) that the asking such a question is futile since answering this question will inevitably lead to another "why question" (which it does). However, I still think this is a valid question.
Think back to the 16th century. There were so many why questions. Why do the planets move as they do? Why does a ball fall down an incline as it does? Why does a top spin the way it does? Newton answered all of these why questions by stating his three laws of motion and his law of gravitation. But we may as well ask why are these four laws valid (which IMO is also a very good question and for which we do know the answer now)? So what he really did was reduce a whole bunch of disparate why questions to just four why questions ?
Seen from this point of view the goal of physics (and if I may be so bold, all of science) is to reduce all why questions to a single why question and show that the rest follow from that once you assume it to be true. We need to find the ultimate question. (Hmmm... Why does it sound like Douglas Adams here
)
So we may ask is there such an asnwer (or to phrase it more accurately - such a why question) to the why question we have posed.
There is. I will provide one definitive and three tentative ones in the following.
But before I proceed further I must apologize for some amount of jargon that I would have to necessarily throw around and which will not make sense to some in this forum (sorry DP for all this gibberish! ) This has to be so because I know of no other way to state these thoughts (which also means according to Feynmann we do not understand these all that well).
First answer: This is the straightforward answer that I would give to any physics graduate. Start with the QED Lagrangian and calculate the potential betweem two charges assuming that electromagnetism is propagated by photons. The potentials come out with the correct sign for the force. (A very simple such calculation is done in Anthony Zee's book where he assumes that the photon is a massive vector boson and sets the mass to zero at the end). This is the primary reason why I thought that Col's and Gothmog's original answer of potentials and energies is not the true answer, because these potentials and energies can be derived from the QED Lagrangian. What we have done is essentially replaced the current questions and all of quantum electrodynamics to one question. Why is the QED Lagrangian valid?
However, this answer is hardly satisfactory. While it has the surity of straightforward calculation it lacks elegance and insight.
The following three do not. However, I cannot prove any of them since I have not seen such a proof anywhere and I lack the knowledge to prove any of them. But they seem to be tantalizingly close to the truth and I wish I could find an explanation for them.
The Second Answer:
The result of the sign of the forces is a result of the U(1) gauge group of the photon.
If this were true (and maybe it is but I have not read so anywhere) then it would be a truly satisfactory and insightful answer. For if we assume that the laws of physics are invariant under the Poincare group then as Wigner showed the photon must have the U(1) gauge group. From this we can derive the inhomogenous Maxwell's equations and the QED Lagrangian barring a simple sign. I find it maddenning that we can explain so much but get stuck on such a little sign.
The Third Answer:
A question of scale?
The sign of electromagnetism is because nature does not allow two similar forces to work on the same scale.
Both Electromagnetism and Gravity are long range forces that work on the same distance scales. So if this were true then we know electromagnetism cannot be a simply attractive force for there is one, gravity. It could not be a simple repulsive force for there possibly is one (dark energy?). So the only remaining alternative is a force that is both attactive and repulsive.
This answer is necessarily tied to the earlier answer because forces arise out of symmetry breaking and all we are saying is that we cannot have similar symmetry breaking more than once at the same lenght and energy scale. Who knows maybe this is true.
The Fourth Answer:
CPT Invariance?
The sign of electromagnetism is because CPT invariance demands it to be so.
If this were true then also it will be a very satisfactory answer. Not only will it explain this sign it also explains the sign of statistics of particles. Loosely speaking we know that we can switch the sign of parity and time so we must be able to switch the sign of C too and hence electromagnetism must be both an attractive and repulsive force. This is once again related to the earlier two answers.
I am sure there will be lot of objections to these explanations. Please let them roll.
Hope I did not dissappoint you too much.
Think back to the 16th century. There were so many why questions. Why do the planets move as they do? Why does a ball fall down an incline as it does? Why does a top spin the way it does? Newton answered all of these why questions by stating his three laws of motion and his law of gravitation. But we may as well ask why are these four laws valid (which IMO is also a very good question and for which we do know the answer now)? So what he really did was reduce a whole bunch of disparate why questions to just four why questions ?
Seen from this point of view the goal of physics (and if I may be so bold, all of science) is to reduce all why questions to a single why question and show that the rest follow from that once you assume it to be true. We need to find the ultimate question. (Hmmm... Why does it sound like Douglas Adams here
)So we may ask is there such an asnwer (or to phrase it more accurately - such a why question) to the why question we have posed.
There is. I will provide one definitive and three tentative ones in the following.
But before I proceed further I must apologize for some amount of jargon that I would have to necessarily throw around and which will not make sense to some in this forum (sorry DP for all this gibberish!
) This has to be so because I know of no other way to state these thoughts (which also means according to Feynmann we do not understand these all that well).First answer: This is the straightforward answer that I would give to any physics graduate. Start with the QED Lagrangian and calculate the potential betweem two charges assuming that electromagnetism is propagated by photons. The potentials come out with the correct sign for the force. (A very simple such calculation is done in Anthony Zee's book where he assumes that the photon is a massive vector boson and sets the mass to zero at the end). This is the primary reason why I thought that Col's and Gothmog's original answer of potentials and energies is not the true answer, because these potentials and energies can be derived from the QED Lagrangian. What we have done is essentially replaced the current questions and all of quantum electrodynamics to one question. Why is the QED Lagrangian valid?
However, this answer is hardly satisfactory. While it has the surity of straightforward calculation it lacks elegance and insight.
The following three do not. However, I cannot prove any of them since I have not seen such a proof anywhere and I lack the knowledge to prove any of them. But they seem to be tantalizingly close to the truth and I wish I could find an explanation for them.
The Second Answer:
The result of the sign of the forces is a result of the U(1) gauge group of the photon.
If this were true (and maybe it is but I have not read so anywhere) then it would be a truly satisfactory and insightful answer. For if we assume that the laws of physics are invariant under the Poincare group then as Wigner showed the photon must have the U(1) gauge group. From this we can derive the inhomogenous Maxwell's equations and the QED Lagrangian barring a simple sign. I find it maddenning that we can explain so much but get stuck on such a little sign.
The Third Answer:
A question of scale?
The sign of electromagnetism is because nature does not allow two similar forces to work on the same scale.
Both Electromagnetism and Gravity are long range forces that work on the same distance scales. So if this were true then we know electromagnetism cannot be a simply attractive force for there is one, gravity. It could not be a simple repulsive force for there possibly is one (dark energy?). So the only remaining alternative is a force that is both attactive and repulsive.
This answer is necessarily tied to the earlier answer because forces arise out of symmetry breaking and all we are saying is that we cannot have similar symmetry breaking more than once at the same lenght and energy scale. Who knows maybe this is true.
The Fourth Answer:
CPT Invariance?
The sign of electromagnetism is because CPT invariance demands it to be so.
If this were true then also it will be a very satisfactory answer. Not only will it explain this sign it also explains the sign of statistics of particles. Loosely speaking we know that we can switch the sign of parity and time so we must be able to switch the sign of C too and hence electromagnetism must be both an attractive and repulsive force. This is once again related to the earlier two answers.
I am sure there will be lot of objections to these explanations. Please let them roll.
Hope I did not dissappoint you too much.
The Last Conformist
Irresistibly Attractive
Seems a bit short for a novel competition ... 
I can't rip you answer to shreds because I do not have the prerquisite grounding in physics. Wait half a year and I'll know that QED Lagrangian!
Can't comment you second answer at all, since I haven't the faintest what a U(1) group is. Can't say anything about the third one either, actually.
The fourth seems weird to me. If like charges attracted and opposite repelled, you'd still get both attractive and repulsive EM forces.
I can't rip you answer to shreds because I do not have the prerquisite grounding in physics. Wait half a year and I'll know that QED Lagrangian!
Can't comment you second answer at all, since I haven't the faintest what a U(1) group is. Can't say anything about the third one either, actually.
The fourth seems weird to me. If like charges attracted and opposite repelled, you'd still get both attractive and repulsive EM forces.
betazed
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Ok. But would you agree with my initial premise that a "why" question like this makes sense?
Took me that much to express my thoughts.
I look forward to discussing it with you.
The fourth one is a bit weird (and it took me quite some time to get my head around it and I am not sure I have got it yet). Hence I used the term "loosely speaking" to describe it.
Took me that much to express my thoughts.
I look forward to discussing it with you.
The fourth one is a bit weird (and it took me quite some time to get my head around it and I am not sure I have got it yet). Hence I used the term "loosely speaking" to describe it.
The Last Conformist
Irresistibly Attractive
It is, I feel, quite another species of explanation than, say, the ones to the Oklo and slippery ice question, but a kind of explanation nonetheless. It's the first question on this quiz that has caused me to think some tolerably profound thoughts, so I guess it was a good question.
(Someone said that the measure of a good theory isn't that it answers alot of old questions, but that it raises many new ones no-one could have imagined before.)
Who's to ask the next question?
(Someone said that the measure of a good theory isn't that it answers alot of old questions, but that it raises many new ones no-one could have imagined before.)
Who's to ask the next question?
Kinniken
Riding with William
A question it is not possible to Google? Hummmm.... This one might be sufficiently hard to google.
Name an animal capable of detecting other animals* by sensing their bodies' electricity.
*not necessarily any other animals; a particular specie or type of animal is enough
Name an animal capable of detecting other animals* by sensing their bodies' electricity.
*not necessarily any other animals; a particular specie or type of animal is enough
Kinniken
Riding with William
Are they??? Ooops... It's not the answer I want.
Rephrased question: Name a mammal capable of detecting other animals by sensing their bodies' electricity.
Rephrased question: Name a mammal capable of detecting other animals by sensing their bodies' electricity.
Perfection
The Great Head.
WHales?
Maj
Emperor
I'll say dolphins.
Perfection
The Great Head.
Bah! whales a WAY better than dolphins!
Go Whales!
Edit: Platypus?! But those aren't awesome!
Go Whales!
Edit: Platypus?! But those aren't awesome!
Kinniken
Riding with William
Actually, they are... Consider:
- one of only two mammal families to lay eggs
- only mammal with venom
- only mammal with a real beak
and...
- only mammal capable of detecting the bodily electricity of its preys (underwater)
They may look somewhat stupid, and are not as impressive as a Whale, but they still have a trick or two to teach bigger and more "evolved" species!
So betazed wins!
Perfection
The Great Head.
Damn Monotremes, they think they're so special because they lay eggs and stuff!
Well they ain't the boss of me!
Well they ain't the boss of me!
Achinz
Hermit of Huangshan
Yep, every Aussie kid knows the cute platypus!
Achinz
Hermit of Huangshan
OK. Probably a simple one (ie Googlable ). What are the two radionuclides monitored for short term and long term radiation hazards from nuclear fallout (one for each) and why?
). What are the two radionuclides monitored for short term and long term radiation hazards from nuclear fallout (one for each) and why?
The Last Conformist
Irresistibly Attractive
I'd been assuming as a matter of course that one was not supposed to use google or the like.
And sans google, I don't know what radionuclids are monitored for that.
And sans google, I don't know what radionuclids are monitored for that.
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