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Mr. Bill has suggested the forum members point out errors, if any, in the "correct" scientific material posted on his website. I have read just three entries: (1) "CORRECTED: NO, INFRARED LIGHT IS NOT A KIND OF HEAT", (2) "LASER LIGHT IS "IN PHASE" LIGHT? WRONG" and (3) "CORRECTED: LASERS EMIT COHERENT LIGHT, BUT NOT BECAUSE THE ATOMS EMIT IN-PHASE LIGHT WAVES" today. I see many factual errors. A few samples below (cut and paste from the website):
1."The infrared light from an electric heater feels hot because the light is EXTREMELY BRIGHT LIGHT". Wrong. It is because most materials (including human body) absorb IR radiation better than visible radiation. The light may be extremely bright, but that is a secondary aspect.
2."If the atoms' emissions weren't in phase, the result would NOT be light that's out of phase. Instead the atoms would absorb light rather than amplifying it". If this is true then (a) spontaneous emission should not happen at all, and (b) all light we see around should have been coherent. Obviously, this is not the case.
3."in-phase photons are nothing unique, and they don't really explain coherence". Then what explains coherence?
4."Even fairly advanced textbooks fail to give the real reason why laser light is spatially coherent". Please read "Lasers" by A.E. Siegman.
5. "in-phase emission only creates amplification of the traveling waves, it does not create spatially coherent light". Wrong. In-phase emission is inherently coherent, spatially and temporally.
6."Lasers create coherent light because of their mirrors". Wrong. Coherence comes from in-phase emission, while mirrors assist amplification.
7. "Laser light is spatially coherent because, among other things, the bouncing light has traveled millions of miles between mirrors". Not true for all lasers. Take for instance, a Q-switched, pulsed Nd:YAG laser. The Q-switch ON time is typically in nanoseconds (ns). Take it to be 100 ns. In one ns light travels one foot. ie, laser action has already happened by the time photons traveled 100 feet between the mirrors - not millions of
miles.
8. "The pure color (monochrome) laser light is ALSO created by the mirrors. Huh? Yes, but the reason for this is not totally straightforward (and it's quite a bit beyond the K-6 level of these webpages!)". [Wow. I'm too tired by now]. The reason for the monochromaticity is totally straightforward, but this requires some knowledge of photons, resonators, cavity modes, gain media and emission linewidths. To Siegman again (there are other good text books too).
In the entire discussion on Lasers, the author hasn't used the term "stimulated emission" even once. It is so vital; Stimulated emission is what distinguishes a laser from ordinary incoherent light sources: photons emitted in a stimulated emission process are mutually coherent. Why no mention of this at all? The discussion on the formation of a coherent wave in a laser system under the heading "LASERS EMIT COHERENT LIGHT, BUT NOT
BECAUSE THE ATOMS EMIT IN-PHASE LIGHT WAVES" contains some genuine nonsense (as I read it in his website today - 7th August 2011). I pity the students (and teachers) who happen to read such material. Enough number of standard advanced textbooks in Physics are available, if the elementary books in the US are not good enough!
I believe while a certain level of solid academic knowledge is sufficient to teach many disciplines satisfactorily, "correcting the wrongs" of those went ahead of us is no mean task. It needs years of study, deep knowledge and wisdom. For instance, QM and GTR weren't born just out of the blue on a fine morning.
Thanks,
Reji
1."The infrared light from an electric heater feels hot because the light is EXTREMELY BRIGHT LIGHT". Wrong. It is because most materials (including human body) absorb IR radiation better than visible radiation. The light may be extremely bright, but that is a secondary aspect.
2."If the atoms' emissions weren't in phase, the result would NOT be light that's out of phase. Instead the atoms would absorb light rather than amplifying it". If this is true then (a) spontaneous emission should not happen at all, and (b) all light we see around should have been coherent. Obviously, this is not the case.
3."in-phase photons are nothing unique, and they don't really explain coherence". Then what explains coherence?
4."Even fairly advanced textbooks fail to give the real reason why laser light is spatially coherent". Please read "Lasers" by A.E. Siegman.
5. "in-phase emission only creates amplification of the traveling waves, it does not create spatially coherent light". Wrong. In-phase emission is inherently coherent, spatially and temporally.
6."Lasers create coherent light because of their mirrors". Wrong. Coherence comes from in-phase emission, while mirrors assist amplification.
7. "Laser light is spatially coherent because, among other things, the bouncing light has traveled millions of miles between mirrors". Not true for all lasers. Take for instance, a Q-switched, pulsed Nd:YAG laser. The Q-switch ON time is typically in nanoseconds (ns). Take it to be 100 ns. In one ns light travels one foot. ie, laser action has already happened by the time photons traveled 100 feet between the mirrors - not millions of
miles.
8. "The pure color (monochrome) laser light is ALSO created by the mirrors. Huh? Yes, but the reason for this is not totally straightforward (and it's quite a bit beyond the K-6 level of these webpages!)". [Wow. I'm too tired by now]. The reason for the monochromaticity is totally straightforward, but this requires some knowledge of photons, resonators, cavity modes, gain media and emission linewidths. To Siegman again (there are other good text books too).
In the entire discussion on Lasers, the author hasn't used the term "stimulated emission" even once. It is so vital; Stimulated emission is what distinguishes a laser from ordinary incoherent light sources: photons emitted in a stimulated emission process are mutually coherent. Why no mention of this at all? The discussion on the formation of a coherent wave in a laser system under the heading "LASERS EMIT COHERENT LIGHT, BUT NOT
BECAUSE THE ATOMS EMIT IN-PHASE LIGHT WAVES" contains some genuine nonsense (as I read it in his website today - 7th August 2011). I pity the students (and teachers) who happen to read such material. Enough number of standard advanced textbooks in Physics are available, if the elementary books in the US are not good enough!
I believe while a certain level of solid academic knowledge is sufficient to teach many disciplines satisfactorily, "correcting the wrongs" of those went ahead of us is no mean task. It needs years of study, deep knowledge and wisdom. For instance, QM and GTR weren't born just out of the blue on a fine morning.
Thanks,
Reji
Above is an unfair and fallacious tactic which I've repeatedly encountered online:
- Labeling opponents with emotionally-loaded, derogatory terms.
To sway the audience to our side, we can ignore arguments and instead just suggest that our opponents are foolish "Conspiracy Theorists."
Example: if women and minorities complain about low-paying jobs, should we say that they're really complaining about their bosses conspiring against them? Yes, but only if we want to twist their words, make them look foolish. Yet in reality, in order to suppress women and minorities, employers don't need to consipre. (To keep people down, employers don'e even need to do anything consciously.)
OK, so now suppose I point out that math modeling is being used as a sort of "medieval doctor's Latin." What's your response? To suggest that I'm not saying what I'm actually saying.
Instead I'm actually "whining."
Whining about "conspiracies."
DING! Illegal move.
How are scientific discussions different than a political ones? In politics the goal is persuasion: to sway our audience using rhetorical tactics. In science, instead our goal is to drill down to reality; to see which side might actually be correct. Scientific discussions require bend-over-backwards honesty.
Besides Feynman's excellent "Cargo Cult Science," another good paper on this is:
The Clinical Attitude Towards Arguments
Peter Suber, "The Clinical Attitude"
Cargo Cult Science, 1974 Caltech commencement lecture, RP Feynman
http://calteches.library.caltech.edu/3043/1/CargoCult.pdf
Keep focused on ideas and do not succumb to the temptation to stray into anything that could be construed as a personal attack.
Part of that honesty is responding to the point made rather than complain about word choices.
Math is required to understand much of physics (as well as much of the rest of science)- there's no way around it. Anyone can learn it if they want to, the books aren't hidden, classes are available. You can even read Feynman's "real" physics books, which require nothing beyond calculus and linear algebra.
I'm sorry, but claiming that it's an artificial barrier is indeed incorrect, a lame excuse at best.
Math is required to understand much of physics (as well as much of the rest of science)- there's no way around it. Anyone can learn it if they want to, the books aren't hidden, classes are available. You can even read Feynman's "real" physics books, which require nothing beyond calculus and linear algebra.
I'm sorry, but claiming that it's an artificial barrier is indeed incorrect, a lame excuse at best.
Peeling an onion, that’s how I see science in general. We peel back each layer to reveal something similar yet not the same, we discuss the new layer but what we really want to do is get to the next one. Thus each layer makes the sum of whole, yet we have to destroy the whole just to prove that fundamentally the onion was an onion after all. But personally that’s what I like about discussion like this; anything that gets people talking about Physics has to be a good thing. In fact anything that gets people talking full stop, is a good thing.
Just one other thing, you tend to defend because your being attacked , but attacking is often a good defense.
Just one other thing, you tend to defend because your being attacked , but attacking is often a good defense.
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