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Locrian

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Posts posted by Locrian

  1. the light doesn't actually travel faster than c, what happens is that the leading edge of the wave gets turned into a peak, so the detector on the other side picks up the peak alot sooner than it should of.

     

    What you wrote there says: "The light doesn't travel faster than c, it just gets detected as if it were moving faster than c." I'd be interested in hearing you justify the two statements. I assume you're discussing the group velocity, but I know of nothing about group velocity that makes your statement make sense.

     

    --------

     

    Keneshin,

     

    The article you linked to is from 2000. There has been a lot of research in the area of negative index (NI) materials since then. It is a fascinating subject. The phase velocity is faster than c, but interestingly, the group velocity travels the wrong direction, opposite to the direction of the energy. The doppler shift is also reversed. The diffraction limit is no longer a limit. Truly, some amazing things happen.

     

    There has always been a great deal of hand-waving concerning how light operates in materials as people try to reconcile the strange behavior with the simple rules the public has been fed for decades. The fact that NI materials cannot be described by those cute one-liners (e.g., light is slowed because it is being absorbed and emitted, or is taking a longer path, etc.) suggests they probably were poor descriptions to begin with.

     

    Evidence of what I'm saying here can be found in the publications of scientists who believed NI materials wouldn't result in negative refraction, wouldn't result in phase velocity greater than c, and wouldn't result in sub-diffraction limit imaging. I can send you to a paper that argues all of those things, and does so via causation. All of those things have been experimentally shown to occur.

     

    Probably the most correct answer to your question - although undoubtedly the least fun - is that claiming a "speed of light" in a material whose index of refraction is wavelength dependent simply doesn't have any meaning. The assumption is still that light travels at c, but somehow some really complicated things are going on that obscure determining this simply. This is one of those assumptions that makes everyone feel better, and is nice to say to people outside science, but has no measurable evidence that I'm aware of. When actually working with the materials, the subject is just more complicated than that.

     

    So the short answer is that some very funny and very weird things are going on here, but that there is no reason to think they violate causation or relativity.

  2. A working prototype of a quantum computer? Not that I've heard of, and not unless your definition of "computer" is pretty lenient. I've never heard of anyone stringing together more than a few qubits at a time, and those only operate under pretty severe restrictions, including being electromagnetically and thermally sealed.

     

    There are still people who think a large-scale quantum computer isn't even possible due to issues with decoherence.

     

    Maybe you've heard something new we haven't 5614?

     

    PS: And thanks for another good link Martin

  3. Well I'm not talking about GR. Acceleration due to gravity isn't mass dependant; acceleration due to friction is, inversley. That heavier objects fall faster than lighter ones that are the same shape and volume is a fact well known to every skydiver.

     

    Can't get more classical or common sense than that.

  4. Just for fun, let me put a different spin on things.

     

    I've been reading a great deal about negative index (NI) materials. People are used to the idea that light travels slower in most materials. The idea that it could travel faster (the phase velocity, at least) in a NI material was not well accepted until 2002 - or later.

     

    Anyways, in 2001 Valanju et. al. published a paper in physics review letters (Phys Rev Lett, 88 187401) entitled “Wave Refraction in Negative Index Media: Always positive and Very Inhomogenous.” They wrote:

     

    In conclusion, we have shown that causality and finite signal speed preclude negative refraction for any waves incident on any material, including NIM. The NIM dispersion implies positive group refraction even when phase refraction is negative, and causes large angles upg between phase and signal fronts and creates inhomogeneous waves that rapidly decay, during and after passage through NIM. The strong distortion of the signal puts severe bounds on the bandwidth of the information that can be transmitted through NIM devices. Negative refraction ray diagrams in all earlier literature do not represent the correct positive wave (i.e., signal) refraction by NIM.

     

    Note their reasoning: causality. Light traveling at a different speed to them suggested a serious problem with how we view the world.

     

    They were wrong. They were writing up that paper the same time negative refraction was being experimentally demonstrated, and that paper was published within a similar time frame. Hows that for a bad day, coming to work to find out your paper that just got printed is already wrong?

     

    So in conclusion, it is easy to be fooled when you see that the speed of light might change into thinking all of physics suddenly crashes at our feet. It doesn't, as Valanju et. al. can tell you.

  5. An impressive bit of modeling, to be sure. I remember reading in a paper once that below a certain size, gold molecules turn purple. I guess it's as they say: "The rules change in the reaches."

     

    I'm somewhat interested in the expeirmental verifications - they used diamond anvil cells I presume? I don't see any information in those links and am too lazy to look on a sunday evening. If you run into anything would you make a quick post of it?

  6. Two things:

     

    1) Scientists have been dealing with light moving at different speeds in a practical matter for as long as relativity has existed

     

    2) Relativity does not actually depend on light's speed never varying; just that all observers see it as moving at the same speed, regardless of their relative velocities

     

    So you can relax! There is reason for plenty of drama if Murphy is right, but not the kind you have in your post.

  7. Once I had to explain how objects fall at the same speed regardless of mass to an older student who at the time had already done a really excellent paper on gravity and orbits.

    Allthough he was able to describe these phenomenons mathematically' date=' he was unable to "translate" the mathematics into a common sense understanding of how it works in everyday life. [/quote']

     

    Well, in everyday life things with different masses don't fall at the same speeds, even if they have the same geometry. Maybe it's not so common sense after all?

  8. Is it possible for an object to achieve the required escape velocity around a planet but not leaving the planet?

     

    Sure. A spacecraft could achieve escape velocity and then turn around and fly back.

     

    Somehow that doesn't seem to be the answer you are looking for. Maybe you could elaborate on the question?

  9. Isn't there funding (large quantities) for projects by "interested" parties and companies?

     

    Sure, just not so much for very high energy physics. And you are right about physics leading the way in many technologies. This has continued to be true regardless of decades where little to nothing has come from hep because physics is more than high energy physics.

  10. Alas, God, as reflected in the known laws of physics, hasn't gotten any smarter since the 1970's.

     

    Hmm. This does not seem the least bit true to me. Of course, the "laws of physics" is a terrible, outdated phrase that has little meaning, so I suppose it depends on your definition, but I would consider the quantum and fractional quantum hall effects laws under any reasonable definition, and they were discovered in the 80's.

     

    I suppose it's easy to understand, when there have been no huge leaps and bounds since the 70's, and with the comparitively low wages offered by academic careers, there's also the issue of demand. .

     

    This of course is very true of high energy physics. I'll point out - as I'm sure you already know - that there have been huge leaps in almost every other area of physics, even theoretical ones, in the past 25 years. It's only at the extreme of one spectrum that we seem to have lost steam.

  11. I'm not aware of any such thing, though maybe when it comes to quasars I'm not aware of much.

     

    Quasars have been a topic of interest because some feel they've been identified as being in galaxies that are younger than they should be, suggesting some of our understanding of quasars isn't good. In some cases it turned out these were optical illusions. Other cases are more difficult to dismis.

  12. Actually, broad areas of theoretical physics end up useful very quickly. Think quantum optics, transistor, GMR, etc. String theory, on the other hand, doesn't have a problem with usefulness yet. It has a problem with being more than fantasy. Mathematics is a beautiful thing, but its not physics until there is experimentation.

     

    Once string theory is burned by the holy brand of phenomenology, it may twist and shape itself to something that is physics. At that time it will face the usefulness problem. To get an idea of how useful it might be, look to all the important social and scientific changes due to work in particle physics over the past twenty years.

  13. I generally agree with swansont, but with a gigantic disclaimer: while an understanding of the underlying processes is important, the degree to which it is necessary depends wildly on your system, your field and your application.

     

    When talking about elementary physical systems it is easy to think in binary when discussing whether you have some more fundamental understanding you say "we do" or "we don't." It is not so easy in other areas. I will use the area I've worked in for a while now as an example: in CVD diamond growth, the actual process of diamond growth is very poorly understood in a general sense. In some simplistic cases a reasonable model is available, but it cannot be said we have anywhere near a thorough understanding of what occurs in the growth process under the variety of conditions it is done.

     

    And what's important here, is that this hasn't prevented the field from making great progress. I believe you can argue that it might have hindered it, but research goes on. There is a vast landscape of possible experiments one can do in this area that will change the outcome of your experiment in ways that are difficult to predict. This gets no one's approval, but it is certainly not the end of the story.

     

    You will hear many, many examples such as that as you study matter in more and more complex systems.

  14. I'm not getting you Martin. I, also agree that the assumption of singularities is unacceptable. But this, to me, has very little to do with the Big Bang. The Big Bang is an unfortunate term that describes the expansion of our universe. Don't you think there are good reasons for thinking it has merit, regardless of what happened right at t=0?

     

    I humbly disapprove of your title of the thread, even if I agree with much of what you wrote.

  15. Heh I remember back in 2001 (or so?) reading Woit's article in American Scientist. I was still an undergrad at the time, but his arguments resonated deeply with me. Its been fun being the contrarian all this time, but now it looks like my skepticism may be - if not a majority - at least a bit mainstream.

     

    Will that take all the fun out of it? Only time will tell. Laughlin stirs people up better anyhow ;)

  16. http://www.pnas.org/cgi/reprint/97/1/28.pdf

     

    The emergent physical phenomena regulated by higher orga-

    n izing principles have a propert y, namely their insensitivit y to

    microscopics, that is directly relevant to the broad question of

    what is knowable in the deepest sense of the term. The low-

    energ y excit ation spectr um of a conventional superc onductor,

    for example, is completely generic and is characterized by a

    handful of parameters that may be deter mined experiment ally

    but cannot, in general, be computed f rom first principles.

     

    Now don't get me wrong, Laughlin tends to have a "I've won a nobel prize, I can act batshit crazy" attitude sometimes. But he's always felt this way, and the number of people who agree with him is growing. As an experimentalist, I couldn't care less whether emergent phenomena exist or it is simply a matter of our inability to compute problems using first principles. Either way, reducing a problem I'm facing too far, all the way to its constituents, is a monstrous waste of my time.

     

    People learning about physics should have many points of view on this issue, and they are typically only given one.

  17. It's only reductionism in the sense that there are only four forces which have any evidence for them. DAMN THAT EVIDENCE.

     

    That's so weird it's hard to respond to. First off, as I noted above, there's evidence for more than four. Secondly, it's still reductionism either way.

     

    Well, you can't predict (for example) the form my table takes if you try to work up from the atomic level, but that's more due to our limit of being able to solve the wave equation.

     

    Ineffective in what sense?

     

    Um, in the sense that you can't use it to solve most problems. For the reasons you stated above. This pair of responses of yours suggests to me that you don't understand what I'm discussing here.

     

    Just saying "science sucks and is wrong" isn't productive in the slightest.

     

    I never said anywhere that science sucks or is wrong. I'm posting this from my office in a scientific lab. I do work in materials science, and my education is in physics. These opinions I'm expressing here are based both on previously published work (including nobel winners such as Robert Laughlin) as well as my own experience.

     

    Nowhere in your post do you really respond to the meat of my argument. I think (though I could be wrong) this is because you are unfamiliar with the subject matter. If there are specific questions I can answer for you I'd be happy to do so.

  18. You have 4 types of force there.

     

    If I was to exert a force - lets say a straight punch.

    Would this fall under gravity? Could it be electromagetic?

     

    I'm stirring up trouble here' date=' but...

     

    Don't buy this kind of reductionism. Or at least don't pay for it. If you take those four fundamental forces and all the fundamental particles, you can't predict the properties of just about anything, and certainly not the properties of materials you need. Of course, you can't do [i']without[/i] them either, but my point is that merely boiling everything down to its constituents (reductionism) is ineffective.

     

    This may be because it is wrong, and there exist emergent phenomena that must be taken into account. Or it may just be that it is just not useful. Either way, keep in mind that our world is full of vast numbers of interesting phenomena, and that filing them away into a few categories is scientifically untenable.

  19. yes we do. gravity, electromagnetic, weak nuclear and strong nuclear. thats all the force there is.

     

    Pop quiz! Which one of those four is responsible for the accelerating expansion of the universe? (Hint: none of the above)

  20. Does that mean that, if we change the energy of the light or radiation striking the glass, such that, the photons can interact with the electrons of the glass, then we can make the glass look opaque ?

     

    Yes. Quartz is clear in the optical frequencies, but tends to be opaque in the ultraviolet (though people sell quartz they say transmits there as well). As for steel, metals tend to be very difficult to image through with almost any frequency of light. The problem is that by the time you find something that will penetrate the steel, you get very specific kinds of information from the other side (if anything at all), which may not be useful. Of course this can be very complicated, and there are many tools out there.

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