Some Thought Experiments (simple ones)

[Frame Dragger]

OK, we've got your number now.

Yah, and I take back the "no one has reported [him]" thing. Sometimes I hate being right about people from first impressions... it makes me more likely to be harsh in an innapropriate situation. The old, "Remember the hits, forget the misses, fallacy.

@Deepak: Thanks for lowering the tone *insert deeply insulting curse*.


Oh look, he ran away. Oooh, I can TASTE the line through his name

 

[DaveC426913]

EDIT: Hey now Dave... I thought he was out of his gourd waaay before #30.

I amended my post.

 

[Frame Dragger]

Ah, my bad... I get... heated in these situations. I don't like seeing intellectual capital (you and kev) wasted this way. This is the kind of thing that turns helpful and outgoing people like you two, into angry pricks like me.

 

[yuiop]

But I have a feeling that even shadow will be considerd a 'thing', say 500 years from now.

You are free to squirm at this!

Certainly a shadow is thing, but a difficult thing to catagorise. It depends on you definition of "thing". If we define "thing" as something with rest mass then a shadow is not a thing and by that definition a photon is not thing either, but normally the word "thing" is not so narrowly defined.

So what is shadow? Is it a thing with zero rest mass and zero energy? Hmmmm... not sure (See later definition by Dave). It can be used to transmit information, but it can not be used to transmit useful information at greater than c.

You seem to be under then impression that nothing with energy can travel at the speed of light. This is not correct. In fact light is a form of energy and can only travel at c in a vacuum. The restriction for relative velocities is that nothing with mass can travel at c. Photons do not have mass. Here is a simple demonstration:
E = \frac{mc^2}{\sqrt{1-v^2/c^2}}

m = \frac{E\sqrt{1-v^2/c^2}}{c^2}

where m is mass. For a photon, v=c and the mass must be zero.

<Edited to remove the qualification "rest" applied to mass, as that implies there are other kinds of mass.>

 

[DaveC426913]

So what is shadow? It is a thing with zero rest mass and zero energy.

This definition may get you into trouble in unforseen ways.

It is probably better to remain cognizant of what a shadow is: an area where photons are blocked. Those photons still obey the laws of physics.

 

[yuiop]

Ah, my bad... I get... heated in these situations. I don't like seeing intellectual capital (you and kev) wasted this way. This is the kind of thing that turns helpful and outgoing people like you two, into angry pricks like me.

Just chill

lol.. please do not use my name in the same sentence as intellectual capital.. its makes me a target and its kinda embarrassing.. I am just learning like most other folks around here...

 

[yuiop]

This definition may get you into trouble in unforseen ways.

It is probably better to remain cognizant of what a shadow is: an area where photons are blocked. Those photons still obey the laws of physics.

I did foresee that there are some problems with my definition. I think I was hoping no one would notice I have edited #34 to be less definite.

 

[Fredrik]

1. A clock is placed on a light beam.

Will the clock stop?

If yes, why doesn't the beam stop altogether?

It's not possible to answer a question that supposes something that makes the theory we're supposed to use to answer the question logically inconsistent.

Light moves as described by null geodesics (i.e. at speed c in inertial frames). Clocks moves as described by timelike geodesics (i.e. at speeds <c in inertial frames). Therefore, you can't put a clock on a light beam.

2. A ruler is placed on a light beam.

Same answer. I actually answered these questions in the thread where you made your first few posts the other day. I recommend that you go back and read that answer again. One of them includes a link to a post that discusses the "photon's point of view" in detail.

3. A massless particle is placed on the beam.

What would happen?

Nothing. (If you mean what I think I mean. You could have been more specific).

4. An electron is placed on the beam.

What would happen?

Electrons are massive, so see my answers to 1 and 2, and my answers in that other thread.

I am nobody to talk of Einstein, but when he did his thought experiments, they were indeed impossible in principle. It's only afterwards that a conceptual framework in which they became possible was devised.

It's not surprising that a person who at the time didn't actually know SR would consider thought experiments that SR say are impossible in principle.

1. Light is at least 'something' if not matter. How could anything move with the speed of light?

2. Photons of light have been proved to possesses particle nature, How can these 'particles' travel with the speed of light.

Unfortunately the answer is very mathematical. There's no way you can understand it without studying for years. You will either have to do that, or just accept the fact that particles with m>0 move at speeds <c in inertial frames, and particles with m=0 move at speed c in inertial frames.

3. The photons of light must be involed in some vibration, oscillation, etc. When time stops at the speed of light, how are such processes possible in the case of photons.

There's no such thing as "at the speed of light". See my earlier comments about the photon's point of view in this thread and the other one.

You mean to say that light is energy. Does it mean that energy (being at least something) is able to move with the speed of light.

Massless particles can (only) move at the speed of light, and they carry energy.

So, what about mass energy equivalence. Mass can be taken to be as a concentrated (unqualified term, I suppose) form of enegy.

Every particle (massless or not) satisifes E^2=\vec p^2c^2+m^2c^4, where m is the mass, p is the momentum and E is the energy.

 

[DaveC426913]

Deepak has revealed him/herself as a crank, promoting a personal agenda. Probably best to not feed the trolls and let this thread die.

 

[ZapperZ]

Since this thread appears to be going nowhere, it is done now.

Zz.