Physics question - help needed

[Nakhui]

Originally posted by Otto
Hortland, it's the same everywhere.  Think of the SOL as a type of boundry between the 'present' and the 'past'.  One reason matter(you)  can't go faster than the SOL is because if you did it would take you into the past (a big No-no).  You are a three dimensional being that is moving at the SOL though Time.  If you could out run that movement you wouldn't go into the future (it dosen't exist yet) but back to into the past.

   My little theory and a dime will get you a ride downtown on the bus so take it at face value:p

I've actually be able to prove this theory....

by traveling very very very fast... turning around so my butt faces forward and then farting... the combined velocity causes my farts to go into the past....

and next thing you know everything is backazzward  

[ra]

Originally posted by Hortlund
Is the speed of light different in vaccum, water or air? Or is it the same irregardless of in what medium?

Do a lookup on Cherenkov Radiation.  Light can slow down, and particles can travel faster than light.

ra

[Otto]

Nakhui,

I sure STEPHEN HAWKING will be in touch and you'll be ask to lecture at Cambridge, with the understanding that no open flames will be allowed

[mietla]

Originally posted by Hortlund
I'm sure you all remember this from high-school physics, but if you sit in a car that travels at 25 m/s and fires a gun forward, and the speed of the bullet is 300 m/s, then the speed of the bullet will be 325 m/s. And if you turn around and fire it backwards, the speed will be 275 m/s. The same is not true of the speed of light, because the speed of light is constant irregardless of the relative movement of the observing or moving body. That is what I mean when I say that the speed of light is a constant.

Take the sun as an example, it revolves around the center of our galaxy at a modest 217 000 m/s. A photon, or ray of light if you will, that leaves the "front of the sun" (i e in the direction of movement) will have the speed 299 792 458 m/s, and not (as one might expect from the car example) 299 792 458 + 217 000. Meanwhile a photon leaving the back of the sun will ALSO have a speed of 299 792 458 m/s and not 299 792 458 - 217 000.

I dunno if there are any physics nerds here who can tell me if we have found an explanation to this, because me being a law-nerd really have no idea, and back when I was in school, no one had the answer to that question.

The correct formula for adding velocities is not

     V = u + w

... but ...

   V = (u + w) / (1 + u*w/(c^2))

This is true for fast photons as well as for slow cars and bullets. It is just that when u and/or w are small, the denominator is very close to a 1, and the formula "simplifies" to  

V = u + w

Since most of the velocities we dealt with until XIX century were very small in comparison with c, no one has noticed that V = u + w is not correct. The approximation is very close.

If one of the velocities you are trying to add is a c (u = c), the formula reduces to

 V = (c + w) / (1 + c*w/(c^2)) = (c + w)/(1+ c*w/c^2)) = (c + w)/(1+w/c) = (c+w)*c/(c+w) = c

regardless of what w is.

Speed of light

Think about it this way. There is an absolute speed limit and it is exactly the same in all (not accelerating) frames of reference . Since all frames of reference are equivalent (a principle of special relativity), it follows that the max achievable speed should be the same in all of them. If it weren't you would be able to tell the difference between them and single out certain "special" frames of reference, which would violate the principle of the theory.

This speed limit is denoted as c.

Now, it just happens that photon in a vaccuum travel with the maximum achivable speed (c). As an unfortunate result physicists "equated"  the two. This resulted in a very popular (but incorrect) statement:

     "Speed of light is the maximum speed possible."

The statement above is false. What is true, is:

      "The light travels (under certain conditions) at the maximum achievable speed c."

[MrCoffee]

Its been years since I've looked into Physics but my own interpretation was that as matter reaches the speed of light, its mass will increase. There is a limit for the mass of matter in our universe (sorry for bad wording). Beyond the speed of light, matter converts into energy. Thats if you can get anything to go beyond the speed of light. Im no expert on the matter. This is just my own understanding of it.

[MrCoffee]

Here you go.

http://www.physlink.com/Education/AskExperts/ae388.cfm

[Hortlund]

Originally posted by mietla

     "Speed of light is the maximum speed possible."

The statement above is false. What is true, is:

      "The light travels (under certain conditions) at the maximum achievable speed c."

Thanks for the reply mietla. I understand everything (hah.. right!) up to this point.

The way I understand that last sentence is:
"light travels at the speed of light" ...which really looks like a tautology in my book.

[Naso]

Very interesting thread (and I understand it better as sober ).

Hortlund, re-read Mietla's answer.

"c" is not lightspeed, is the constant (apparently) "maximum speed limit" of the universe, according to this, nothing in the universe can exceed this limit (can you imagine the speed limit ticket you'll got?? ).

It happens that the photon is one of the few particles that can reach, generally, this speed limit, so in popular culture (mine, since 5 minutes and a BBS thread ago) "c" is equated to lightspeed.

The correct statement is:

Lightspeed is generally equal to universe's maximum speed "c".

[Angus]

Some  Physics experts don't belive in the absolutness of the light speed. And as a matter of fact, danish scientists managed to "slow" down light to the stunning speed of only 100 km/h if my memory serves me right.
There are many things in the universe unexplained, including the big ones as "what is gravity". REALLY!!

[Holden McGroin]

Originally posted by Hortlund
....if you sit in a car that travels at 25 m/s and fires a gun forward, and the speed of the bullet is 300 m/s, then the speed of the bullet will be 325 m/s. And if you turn around and fire it....

Einstein started to think about this and then asked the question how do you know the car is doing 25 m/s? 25 m/s in relation to the side of the road, but how fast is the road moving, how fast is the Sun orbiting, and how fast is the galaxy moving, etc...

Your perception of velocity depends upon your frame of reference.  As long as the car is at a constant velocity, all the newtonian phenomena work within the car as though the outside of the car does not exist.  

So one could, by his observances in a closed non accellerating room, validly say he was at rest and all other things are moving in relation to that room.  

These thoughts culminated in the idea that there is no universal gridwork from which all is measured.  Gridworks could be started anywhere, and all would be equally valid.

About that time, experiments were undertaken where the speed of light from distant stars was measured when the orbit of the earth was moving toward the star and again in six months, when at the opposite point of the orbit.

These experiments showed that the orbital velocity of the earth was not a factor in the speed of light emitted from these stars.

The only solution to the apparent pardox was that there was no paradox at all.  The speed of light was the absolute from which all was measured and the time and distance had to change in order to have all observers see the speed of light in vacuum as the apparent constant it is.

One cannot travel faster than light because from a ship travelling at near light speed and headlights peer out ahead and SR says the light must travel away from the ship at the speed of light in vacuum.  But on a planet the ship travels past, the headlights of the ship are also travelling at c, so the ship must be going slower than the photons from its headlights which are at v = c.

[Heater]

you guys need to smoke more dope

[Angus]

Were there so advanced measurments at the time, - . measuring light travel at different orbital positions?
I mean, from a star straight across in the same horizontal line as earths orbit,  the distance is about 1000 light seconds, or 16,6 light minutes if you prefer. Measured against just the nearest stars (4-6 light years), that is like a crowberry in hell. Please tell me more abouty this, like how and when and so, - very interesting!!!:)

[mietla]

Originally posted by Angus
Some  Physics experts don't belive in the absolutness of the light speed. And as a matter of fact, danish scientists managed to "slow" down light to the stunning speed of only 100 km/h if my memory serves me right. REALLY!!

Not some physicists, all of them. Speed of light is not constant, c is.

Speed of light (not c, but the real velocity with which light propagates) depends on a density of the medium in which it travels.

[Holden McGroin]

Looking at the same star at opposite points in the orbit should have produced a velocity difference of over 133,318 mph (213,300 kph) due to the advancing and retreating of the earth's orbital velocity through the supposed ether.  This was the biggest velocity difference anybody could think of and it probably still is a century later.

Observations showed that the velocity difference did not exist, and that caused Einstein to begin scratching his head.  

An experiment was designed by Fizeau (1819-1896) to find the speed of light. A light beam is reflected to a distant mirror, passing through the teeth of a wheel rotating at high speed. The teeth cause a strobe effect, and the speed of the teeth is adjusted until the reflected pulse of light is stopped by the next tooth.

Time and distance of the apparatus is known so the speed is calculated.

[MrCoffee]

Nobody has discovered or solved the mystery of why the max speed of light is c=299'792'458 m/s.

These thoughts culminated in the idea that there is no universal gridwork from which all is measured. Gridworks could be started anywhere, and all would be equally valid.

Speed of light and time

Followed by

Lorentz Transformations