OT:Tempted to get this book

[AMF]

If you're looking for a book that deals with "science as a whole, in a new way" I would try A New Kind of Science
by Stephen Wolfram. Well respected, intriguing, cool.

See:

http://www.amazon.com/exec/obidos/tg...00720?v=glance

[deccan]

aiken said:
Actually t'= t*sqrt(1-v^2/c^2). There's nothing about acceleration here. Accelerating frames are matter of special relativity. Also twin paradox can be solved in special relativity only (edit: sorry not special, but general relativity in both cases).

Ah yes, you are right. I was thinking about the wrong thing. Let me try again: the author's contention that the relativity of motion (which is true) makes time dilation logically suspect is wrong because of the symmetry of time dilation while the twin paradox effect is actually an example of non-symmetry.

[Captain Kwok]

douglas said:
His analogies using people in place of various objects are flawed in that a person is a very complex and inefficient organism and is constantly expending energy in ways not strictly necessary to do work.

Actually, our bodies are incredibly efficient, especially when compared to any machine we've built.

[Kamog]

The author says, "As we all know, perpetual motion machines are impossible,..." and gives the example that if you drop an object dropped into a tunnel through the Earth it would oscillate back and forth endlessly, saying that this result violates the laws of physics.

It does not. Perpetual motion machines are, in fact, possible if all friction is eliminated. Dropping an object into a tunnel through the earth will oscillate endlessly if there were no air inside the tunnel to create friction. If there is some air in the tunnel, the object's energy would be gradually lost as heat and the oscillation would decay and eventually stop, as expected.

It does not require the expenditure of energy to hold an object still in one place! You don't need a constant energy source to keep a fridge magnet stuck to the fridge or have a heavy object resting on a table. The object doesn't move because all the forces on the object are in balance and cancel each other out.

A light beam shining through glass will slow down and it does speed up again once it exits the glass. Why does it speed up again when it exits the glass? That's a good question, and I don't know why. I'm very curious as to what the reason is. But I think the reason a block of glass will heat up when light is shined though it is because the glass is imperfect and not completely transparent. Part of the light is absorbed and turned to heat. So not all the light emerges from the other side.

Regarding the Twin Paradox Thought Experiment: Hmm, I never thought of that paradox! I would very much like to know how to resolve this paradox.

[Fyron]

Kamog said:
A light beam shining through glass will slow down and it does speed up again once it exits the glass. Why does it speed up again when it exits the glass? That's a good question, and I don't know why. I'm very curious as to what the reason is. But I think the reason a block of glass will heat up when light is shined though it is because the glass is imperfect and not completely transparent. Part of the light is absorbed and turned to heat. So not all the light emerges from the other side.

It doesn't actually slow down, it just refracts within the glass and appears distored...

[Renegade 13]

Imperator Fyron said:

It doesn't actually slow down, it just refracts within the glass and appears distored...

Light does slow down through different mediums. If I recall correctly, light travels quite a bit slower through water than it does through a vacuum. Or it might be faster, I'm not sure. (If I'm totally wrong on this point, please correct me, but it seems to be what I remember from physics Last year). Therefore, the only thing that can exceed the speed of light, is light itself (depending on the medium)

[deccan]

Renegade 13 said:
Light does slow down through different mediums. If I recall correctly, light travels quite a bit slower through water than it does through a vacuum.

Yep, light can even be "stopped".

Scientists Bring Light to Full Stop, Hold It, Then Send It on Its Way

[Aiken]

Slowed light is virtual phenomenon. Once photon from light ray collides with atoms of medium it transfers its energy to atom and disappears, but atom goes to hugher energy state. After some time atom re-emits photon with similar wavelenght in the same (if medium has no lens ability) or different direction and then atom goes back to initial energy state. This effect will occur many times until photon leaves meduim. Since cycle of "absorbtion-reemission" is not instant, it gives effect of "slowed light".

edit: note, that it's a very primitive explanation which assumes that photon bahaves itself as a particle. But in real world it also behave itself as a wave. And things become slightly more complicated. But the principle remains the same.

[narf poit chez BOOM]

Excuse me, but if I push on a block of wood and you push on a block of wood and we both have equal strength, given your arguement, neither of us would be expending energy. However, I think in half an hour you would say otherwise, no mater how balanced the forces are.

[Fyron]

narf poit chez BOOM said:
Excuse me, but if I push on a block of wood and you push on a block of wood and we both have equal strength, given your arguement, neither of us would be expending energy. However, I think in half an hour you would say otherwise, no mater how balanced the forces are.

Erm... the difference is that the refridgerator expends 0 energy to hold the magnet in place. The point was that not _all_ stationary objects require energy to remain stationary. Certainly, you can waste energy on an object that doesn't move in the end, but that is not the same thing. When pushing a block that isn't moving, you are not transfering any energy to it. The force you apply is not enough to overcome the counterforces involved, so no work is done on the block. As a result, its energy does not change. You have used energy, but that is for an entirely different reason. It requires a constant source of energy to keep your muscles contracted.