# The science threads - Physics



## chevy (Nov 8, 2003)

Who has extra brain cells to share ????

This is for heavy Café addicts: Physics ! Any body wants to discuss that ?

Scientific American: The Future of String Theory -- A Conversation with Brian Greene The physicist and best-selling author demystifies the ultimate theories of space and time, the nature of genius, multiple universes, and more


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## Arden (Nov 9, 2003)

I haven't done much with this in recent years, but I have a buried fascination with quantum physics.  I actually gave a speech on it my freshman year of high school, much to the boredom of just about everybody.


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## chevy (Nov 9, 2003)

Quantum phyiscs is far from boring... if you explain it correctly... look at Feynman's lectures ! Fantastic.


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## Trip (Nov 9, 2003)

What, exactly, is the string theory?


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## chevy (Nov 9, 2003)

The second word of your question makes it difficult to answer it 

You may look at http://superstringtheory.com/ for a very good description at several levels.


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## Trip (Nov 9, 2003)

Wow.
I really like the idea of having an escape velocity FASTER than the speed of light. *The idea of black holes.

But that doesn't make sense to me, if a black hole had a escape velocity that large then how does it exist? Wouldn't it pull its self into its self? Wow...negative space is the result I guess.

Strange. I never really understood any of this before.

Meh, I'll read more whenever I get the time.


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## chevy (Nov 9, 2003)

Why would an esacpe velocity faster than the speed of light be a problem ? It just means that nothing can reach this escape velocity, so nothing escaped from the black hole. 
The escape velocity does not really "exists", it's a definition, like the equator...  it's perfectly defined but does not include any energy, material or information. So it can be as fast as one wants.


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## chemistry_geek (Nov 9, 2003)

This past week on PBS I saw two of the three part series detailing String Theory.  It was hosted by Brian Greene.  Interesting stuff, but so far a lot of what these physicists are working on has not been able to be observed or tested in the laboratory.  With that fundamental problem of a lack of real world testing, many of these physicists admit that this indeed is not science YET, but rather philosophy.  I read the article in Scientific American at the local library yesterday, and I tried to check-out the book but someone else had it.  It sounds interesting, but I don't think that most people are going to understand it without the mathematical background that the physicists are using to work through these theories.  I recall from the conversation in Scientific American that the coordinates that they are using to describe the position of a particle in space are not the same cartesian coordinates that we all used to working with, i.e. x, y, z.  Rather, they are using these coordinates in a matrix with probablilites, and the problem with matricies is that multiplication is not commutative, A*B does NOT equal B*A UNLESS the matrix is diagonal.  While I know this from taking one semester of Linear Algebra, I do not know why this is so; there is probably some deep mathematical theories or proofs that explain that.  The math these guys use is intense and trying to explain Super String Theory to the general public without it may be a tough sell.  I also recall that the model uses 11 dimensions and that the physicists posit that an currently unobserved but supposedly existent particle, the graviton, leaves the surface of our dimension and goes to another dimension.  The physicists say that this is purhaps why the universe will continue to expand indefinitely since gravity in our universe will get weaker with time.

This theory may appear to explain a lot, but until we can observe some facts that correlate with the theory, or rather hypothesis, I think this will remain a very elaborate mathematical description that possibly explains the universe.  If something can't be observed or measured, then it doesn't exist, scientifically speaking.


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## chevy (Nov 9, 2003)

I don't agree with you. Theories are never observed or emasured. They are verified by experimentation and when possible by predictions.

The string theory is in its infancy and has still a long path to go before being as verified as the relativity or the quantum theories are. Nevertheless is seems very promizing. And the work of Brian Greene is also to make it easier to understand like Einstein work was also to explain the relativity theory so that others can understand it and test it.


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## RacerX (Nov 9, 2003)

Most of my studies in physics tend towards the study of fields rather than particles/strings. I enjoyed General Relativity and the large scale structure of the universe quite a lot (I was never one for calculating out solutions or individual paths, I always wanted to see the large global views of things), and also spend some time looking into things like Quantum Field Theory and Gauge Theory. I had a professor who did some work in String Theory, but I never took much time to look very closely at it.

In Gauge Theory you have something very much like extra dimensions but they are not physical in nature. What I mean by that is that they do not act in the same way that the three physical dimensions work, these are degrees of freedom that take on group structure (Lie Groups actually). There is a full range of 6 additional degrees of freedom associated with every point in space-time. Looking at all these extra degrees of freedom as fibers you can studies them over given paths producing fiber bundles... which starts getting into the type of mathematics I was doing.

Things like the path of an electron threw a magnetic field (which is usually done via probabilities in Quantum Mechanics) can be thought of as connections over these fiber bundles (the bundles take on a manifold structure). These connections are very much like the connection defined by Levi-Civita to help study General Relativity. The first Gauge Theory (though it wasn't originally thought of as such) was Maxwell's Equations. Gauge Theory was "out of fashion" until Yang-Mills Fields was introduced in the mid 50's.

As for the idea of proving theories, the time honored tradition has always been to create a theory that models what we know about nature, then when the model predicts what we know is there point it to something which we didn't know and see if the model holds up. Repeat until the model breaks then fix it. It really shouldn't be that hard to get String Theory to predict something that is within observation that other theories fail to produce.

The problem with physics is that it is very expensive and has some major egos, both of those put together mean it is slow to recognize when the wrong path has been taken or to try out a number of different paths instead of just a few.


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## Cat (Nov 9, 2003)

> With that fundamental problem of a lack of real world testing, many of these physicists admit that this indeed is not science YET, but rather philosophy.


 Init.flamewar: are you implying that philosophy would not be science ... ?


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## chevy (Nov 9, 2003)

chemistry... said:
			
		

> With that fundamental problem of a lack of real world testing, many of these physicists admit that this indeed is not science YET, but rather philosophy.





			
				Cat said:
			
		

> Init.flamewar: are you implying that philosophy would not be science ... ?



Philosophy can be scientific, it does not have to. What chemistry is proposing is that this theory cannot be accepted as science as it is not yet demonstrated. It does not imply that philosophy cannot be made with a scientific approach.


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## chevy (Nov 9, 2003)

If philosophy can lead to physics, physic can also lead to philosophy, mostly when it changes our view of the world.



			
				http://superstringtheory.com/blackh/blackh4.html said:
			
		

> "perhaps spacetime geometry is not something fundamental in string theory, but something that emerges in the theory at large distance scales or weak coupling. This is an idea with enormous philosophical implications"


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## RacerX (Nov 9, 2003)

chevy said:
			
		

> What chemistry is proposing is that this theory cannot be accepted as science as it is not yet demonstrated.



I hope not, because it throws out a ton of real science. 

Newtonian physics (which is the heart of our space program) has been shown not to work as a realistic model of gravitation, and yet we still rely on it for a great deal of science today (because for most things the results of Newtonian physics aren't different enough from General Relativity to make using the harder calculations a requirement).

Many things have been disproven or replaced with better models that are still in use as tools in science today. And just because some things prove to be a dead end (like the Steady State Theory) doesn't mean that they have been removed from science or wasn't science before a better model was proposed.

In the area of String Theory we have a model of nature. This is a mathematical model based mainly on our current physical understanding of nature. It is science. It is the most pure form of science. It is science in the process. 

Real science is dealing with unknowns. Real science is the process, not the end results. Asking questions about what you don't know, not resting on what you do know. Theory is the heart of science. 

Any one who is preaching _theory cannot be accepted as science_ is teaching science in a junior high school.



On the other hand, what I was doing was philosophy. My main area of study was mathematics and I didn't care if any of what I did was ever applied to anything. It wasn't the point. My work on tight immersions and embeddings of both polyhedral and smooth manifolds had no application to any science I know of. The technique I developed for studying regular homotopy of orientable manifolds (using contour diagrams) is about as philosophical in nature as you can get.

Philosophy can be safe and clean. Science is often dangerous and dirty. 

I never got _into science_ enough to get dirty, I just enjoyed playing with the mathematical models. I surely wouldn't have the guts to stake my career on any of the "physics" I was ever doing. And I would never have tried to publish any results I came up with in anything other than mathematics journals.

I have great respect for those who base their careers on the cutting edge of science, because that is where the real science is.


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## Arden (Nov 11, 2003)

Chevy, I knew you liked physics the first time I saw one of your posts from your title. 

Which raises another interesting issue.  The way they describe the issue with Schrodinger's cat, etc., it makes it sound like the result hasn't happened until you look at it, at which point it is determined if the particle is here or there, or the cat is dead or not, etc.  But to me it seems like it has happened for sure, and you don't know it until looking at it... it's all very confusing.

I also haven't researched anything in this issue for about 4 years... I will be taking a course in physics at some point during my 2 years at junior college, and I might read about it before then just to satisfy my curiosity.

Anybody read Greggory Benford's Cosm?  Not exactly feasible in practice, but a good read nonetheless.


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## chevy (Nov 11, 2003)

arden said:
			
		

> Chevy, I knew you liked physics the first time I saw one of your posts from your title.
> 
> Which raises another interesting issue.  The way they describe the issue with Schrodinger's cat, etc., it makes it sound like the result hasn't happened until you look at it, at which point it is determined if the particle is here or there, or the cat is dead or not, etc.  But to me it seems like it has happened for sure, and you don't know it until looking at it... it's all very confusing.



Indeed it is confusing. This is a mental experiment. If you take the theory to its ultimate meaning it means that "it happens in the past at the moment you open the box". Which of course is nonsense.

The current theory is more complex and has a lot to do with all interaction between degrees of freedom that reduce the probability of one or the other event making that thing "happens" really, and not only potentialy at macroscopic level.


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## chemistry_geek (Nov 12, 2003)

In the PBS television special, the physicists themselves said that unless there is "real world testing of this theory, it is philosophy, not science, YET".  Please note, I'm not making that statement, but someone else in the television special did.


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## chevy (Nov 12, 2003)

If the TV said so... sometimes I may disagree with the TV.


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## chevy (Nov 12, 2003)

Back to the theme of the thread. I was not so much discussing philosophy against science, but more about the implications and significations of the string theory.


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## chevy (Nov 15, 2003)

Am I asking for something impossible ?


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## RacerX (Nov 15, 2003)

chemistry_geek said:
			
		

> In the PBS television special, the physicists themselves said that unless there is "real world testing of this theory, it is philosophy, not science, YET".  Please note, I'm not making that statement, but someone else in the television special did.



That is exactly why TV is the wrong medium to teach this in. Any dictionary can tell you that they were wrong for saying that. A theory is as much valid science as is experimentation. 

When you put people, their ideas and their egos on TV your going to get mostly ego. And actually this is the problem with Physics today. A few people have made a name for themselves and are now finding it so important to defend what got them there that they don't care about the alternatives to their ideas.

A great example is the way they all (and now all of them do it) explain extra dimensions in space-time. The _roll-into-a-tube-which-looks-like-a-line-from-a-distance_ party line is sad. Totally doesn't actually tell people what is going on and now some physicist actually think that is the way it is because they don't have the mathematics background to truly understand what is going on.

The most important part of science is being lost because if you don't have a name your ideas are not important. If someone like Hawking says something, question it. Your a scientist, that is what you are supposed to do... question it! Is it right? is it complete? What is the whole story? Ask the questions and then find out for yourself.



			
				chevy  said:
			
		

> Back to the theme of the thread. I was not so much discussing philosophy against science, but more about the implications and significations of the string theory.



As with most theories, there is a modeling period. That is to say you rework the theory over and over again to match nature as you know it. There are a number of theories right now that cover most of the same things as strings. As I said, I like Gauge Theory the best of those which provides for everything via a 10 dimensional space-time (6 of those being group-like degrees of freedom and not space-like dimensions as we are use to).

It is hard to talk about these things at these types of levels. I know from my personal experience in my research that once you pass a certain level of understanding which most of the people around you have you become isolated from them. I was very fond of many of my professors and loved sharing my research with them, but after a point certain point in time it became very hard to convey everything that I was so excited about. They saw that I was excited and listened all the same, but I soon realized that they weren't following me.

That was with people who had the levels of experience to maybe understand what I was doing. With other people it was even harder to talk about stuff.

Most of what is significant of string theories has direct effects on other theories in ways that are hard to understand. And (as with most physics today) there is going to be egos and posturing involved. Watching the PBS show on it I was reminded of why I got out of physics to begin with... the egos are incredible.

That is not to say that they aren't there in mathematics. I ran straight into someone's ego back in 1994 when I reframed a discovery of his in a way that made the discovery less of a break threw in the field and more of a break down in the definitions being used.


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## chevy (Nov 15, 2003)

RacerX said:
			
		

> It is hard to talk about these things at these types of levels. I know from my personal experience in my research that once you pass a certain level of understanding which most of the people around you have you become isolated from them. I was very fond of many of my professors and loved sharing my research with them, but after a point certain point in time it became very hard to convey everything that I was so excited about. They saw that I was excited and listened all the same, but I soon realized that they weren't following me.



I think that the effect of science can be explained when we understand it correctly.

It's just difficult to always understand it correctly.


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## Cat (Nov 17, 2003)

I'm sorry chevy, for partailly hijacking the thread, but I really disliked that quote. I don't know enough about string theory to partecipate. However, maybe I can humbly suggest that you somewhat change the nature of this thread. Science is not synonymous with physics, and string theory may be a bit far-fetched for a forum discussion. I think that allowing for more breadth would be good, because it would elicit more partecipation.


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## chevy (Nov 17, 2003)

That's a good point, let me think about something else.


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## Captain Code (Nov 20, 2003)

I'm a little bit late to the game here, but I thought I'd throw in a comment, which I don't believe has a lot to do with string theory, but is in response to a previous post.

There is actually an escape velocity faster than light according to Stephen Hawking.  He has proven that there is some radiation emitted from black holes.  So this either proves that what is coming from the black hole has no mass so it's not drawn into the gravity of the black hole or that the velocity is high enough as to escape the pull.


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## RacerX (Nov 20, 2003)

Captain Code said:
			
		

> There is actually an escape velocity faster than light according to Stephen Hawking.  He has proven that there is some radiation emitted from black holes.  So this either proves that what is coming from the black hole has no mass so it's not drawn into the gravity of the black hole or that the velocity is high enough as to escape the pull.



Hawking's theory (known as Hawking Radiation) does not require anything to go faster than the speed of light.

The theory works like this:

Every where in the universe virtual particles are popping into and out of existence. These are done in pairs, in which one particle is matter and the other is antimatter. Hawking theorized that on the edge of an event horizon (the boundary between a black hole and the rest of the universe found at _R=2M_, where _M_ is the mass of the black hole) if these particles popped into existence, one might fall into the black hole while the other escapes as radiation. In keeping with the fact that something can't come from nothing, Hawking said that gravitation from the black hole provided the energy to keep the virtual particles from disappearing. In a sense, the black hole is bleeding away it's mass-energy in the form of gravitational tidal forces. Given that, Hawking theorized that black holes would eventually evaporate unless fed by some other source.

Note: by definition a black hole is any large body whose radius _r_ is less than _R_ where _R=2M_ and _M_ is the mass of the body. As I recall Hawking came up with this theory around 1974-76.


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## Cat (Nov 21, 2003)

Didn't very recently some laboratory publish something on going actuallly faster than the speed of light? ... I'll go find a link now ...

Edit: found some:

http://news.bbc.co.uk/1/hi/sci/tech/841690.stm

http://physicsweb.org/article/news/4/7/8/1

http://www.nec.co.jp/press/en/0007/1901.html


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## chevy (Nov 21, 2003)

Still, no mass and no information travel faster than light !


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## Arden (Nov 21, 2003)

That's a good topic... what are we going to do about space travel if we can never go faster than the speed of light?  We may hypothetically be able to get within kilometers of it (which, according to the Google calculator, is 299,792,458 m / s), but we can't pass it.

At that rate, it will take a space vessel at least 5 years to just get to the nearest star to our system, much less a system with an inhabitable planet.  Will we choose to suffer the wait, possibly freezing our bodies to preserve our nature or inhabiting a colony ship until it arrives at its destination?  Will we consign to stay put on Earth, or at least colonize our local friendly neighboring planets and moons?  Will we discover a way to break the laws of physics?  Who knows?

The answer, no matter how you argue it, is nobody right now.  But we'll see.


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## Captain Code (Nov 21, 2003)

RacerX:  now that you explained it, I remember how it worked, and it was what you said, and not exactly what I thought.  But, Cat is right about going faster than the speed of light.  Those scientists in the articles he listed have proved it.  It may  just so happen that when you go faster than light you go back in time as well.

I think someone will discover how to fold space-time and we will not really go faster than light, but only have to travel a short distance, as we pull 2 parts of space very close together and go from one point to another that is "physically" hundreds or thousands of light years away in a matter of seconds.


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## Arden (Nov 21, 2003)

I think the problem lies in trying to imagine it now.  It would be like going back 300 years and asking someone, one of the colonists perhaps, what they think a good design for a computer would be.  You'd have a hard time even explaining the basics of computing without a working model because that's so out of their league, just as space travel beyond the conventional means is out of our league.

I say this because I was thinking about how we'd accomplish what the cap'n described, folding space and time.  Then I realized that we can never accomplish it until we understand the problem, and what's a better way to understand a problem than to compare it to something you already understand?  Some say it's as if space and time were a piece of paper, and you simply fold the paper to connect A to B.  It may be, but until we can understand the concept of extending this to the 3rd or 4th dimension, we can never really know.


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## Cat (Nov 22, 2003)

IIRC som etime ago scientists succeeded in encoding information in a beam of light. The let it pass through a gas or crystal (can't remember) and the beam would store information about this (will look for links). 
BTW. can't you store information in a beam of light through polarization? IT would be enough to encode 1 & 0 so technically enough for anything...

EDIT: link for the crystal

EDIT2: link one and two for polarization.


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## Captain Code (Nov 22, 2003)

If I understand you correctly, fiber optics stores information in light in a sense.


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## chevy (Nov 22, 2003)

Cat said:
			
		

> IIRC som etime ago scientists succeeded in encoding information in a beam of light. The let it pass through a gas or crystal (can't remember) and the beam would store information about this (will look for links).
> BTW. can't you store information in a beam of light through polarization? IT would be enough to encode 1 & 0 so technically enough for anything...
> 
> EDIT: link for the crystal
> ...



Of course information can be encoded in a light beam.


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## Cat (Nov 22, 2003)

chevy said:
			
		

> Still, no mass and no information travel faster than light !


 This was why I posted about it ...


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## chevy (Nov 22, 2003)

I'm not sure I understand you.

No information, no mass, no information travels faster than light for a long time/distance.

Phase can be faster than light.
And we know that quantum states can be "unlocal". As of today, it is still impossible to tranfer any information from point A to point B in a time shorter than the distance between A and B divided by c (the speed of light constant).

Can we fold space to travel faster ? We may be able to localy fold space, but doing that on a large scale to accelerate interstellar travel will probably require more energy than what we can ever produce.


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## Cat (Nov 22, 2003)

Ok, we are probably both nit picking here: if you can make light go faster than light in vacuum, then you can transmit information faster than light in vacuum speed. However, there's a whole bunch of encoding and decoding which probably cannot take place at the speed of light, so if I want to send you the message "no worries?" through a telegraph operating with the super-light speed light, the pulses would obviously travel faster than light in vacuum. However, I need to tap the telegraph and you need to decode the lines and dots, etc. So what do you consider as "time to transmit information"? All from encoding to decoding? Or just the time the message spends in the channel? I cinsidered the second option and if indeed light can go faster than light in vacuum then the time the message spends in the channel will be shorter than the distance between A and B divided by c. Maybe it depends also on what exactly you call information, but things get rather fuzzy there.

I wholehartedly agree on your amended statement "... for a long time/distance".


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## Darkshadow (Nov 23, 2003)

Yeah, I can't see how a vacuum would be stretched over a long distance.

Well, not _easily_, anyway.


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## chevy (Nov 23, 2003)

Cat said:
			
		

> Ok, we are probably both nit picking here: if you can make light go faster than light in vacuum, then you can transmit information faster than light in vacuum speed. However, there's a whole bunch of encoding and decoding which probably cannot take place at the speed of light, so if I want to send you the message "no worries?" through a telegraph operating with the super-light speed light, the pulses would obviously travel faster than light in vacuum. However, I need to tap the telegraph and you need to decode the lines and dots, etc. So what do you consider as "time to transmit information"? All from encoding to decoding? Or just the time the message spends in the channel? I cinsidered the second option and if indeed light can go faster than light in vacuum then the time the message spends in the channel will be shorter than the distance between A and B divided by c. Maybe it depends also on what exactly you call information, but things get rather fuzzy there.
> 
> I wholehartedly agree on your amended statement "... for a long time/distance".



Here we must differentiate the speed of light as being the speed of any part of light (a photon or a group of photons) and the physical constant "c" that is equal to the speed of light in vacuum. No physical entity can go faster than "c" over a long distance (I use long distance because over short distances other phenomena can happen like tunneling that obey other, non strictly causal, rules... the "long distance" limit is normally microscopic but may be quite large in places of extreme gravitation). Phase of a phenomena can be faster than "c". This does not mean that the phenomena is faster than "c".


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## Cat (Nov 23, 2003)

Well, I would ask you to define "phenomenon" then, because that concept is probably just as fuzzy as "information".
If the phase can travel faster than c and I can consider the phase as information, then information can travel faster than c. 

chevy - I am no physicist, so if I am right out wrong, please tell me so. I may have misunderstood some concepts or treating them as meaning something different. I still suspect that we probably both agree, but are having linguistic issues of how some concepts are defined.


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## chevy (Nov 23, 2003)

Hi Cat,

You cannot considere phase as information in this case, because if you change it at time to at place xo, it will not carry the modification at place x1 and time t1 if (x1,t1) canot be reached from (xo,to) with a speed smaller or equal to "c".

So basically it's like a wave: If you look at a wave on the lake, the small ripple on the top of the wave can go faster than wave itself... but it doesn't go as far as the wave goes as it is continuously replaced by a new ripple that starts at the end of the wave, overtakes it and dies at the front of the wave. The energy-mass-information is in the wave, not in the ripple.


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## Cat (Nov 23, 2003)

Thank you chevy, now I know where my reasoning was flawed.


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