Neutrino apparently moving faster than light
- Thread starter argor
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Not sure if I'm being helpful here but this helped me a lot when trying to understand the speed of light:
Don't get hung up on the speed of light. There's nothing terribly special about light as such. C is the speed of electromagnetic waves or radiation. Light is the range of these that human eyes can see. Electricity is another. The speed of gravity another.
The speed of light can be a bit misleading, but I suppose it's used because it's easier for the bigtabs' of the world to grasp than "The speed of electromagnetic radiation".
Don't get hung up on the speed of light. There's nothing terribly special about light as such. C is the speed of electromagnetic waves or radiation. Light is the range of these that human eyes can see. Electricity is another. The speed of gravity another.
The speed of light can be a bit misleading, but I suppose it's used because it's easier for the bigtabs' of the world to grasp than "The speed of electromagnetic radiation".
The expansion of universe refers to stretching of space time itself, hence is not comparable to speed of light, which refers to speed to energy transport.
By that, I meant that an inertial reference frame moving at the speed of light is unphysical.
Magnetism/gravity are irrelevant to it.
I have a question or 2 similar to arwins
imagine 2 spaceships traveling in opposite directions at 100mph they are moving away from each other at 200mph - everyone agrees with me so far.
so if they both accelerate to .45 c they would be traveling apart at 0.9 c - everyone still agree ?
0.5 c - they would be traveling apart at c -everyone still agree? speed moving apart = sum of the 2 speeds
now if 1 ship goes 1mph faster its now longer sum of the 2 speeds why what changes with the 1 extra mph ?
q2: if i shine a torch in front of me imagine a phonton thats travelling out of the torch at c if I start walking backwards does the photon slow down to compensate ? and how does it know im walking backwards ?
q3: If iI sneak up behing arwin and shine a torch in the opposite direction he is facing, does that mean he will never be able to walk forward
imagine 2 spaceships traveling in opposite directions at 100mph they are moving away from each other at 200mph - everyone agrees with me so far.
so if they both accelerate to .45 c they would be traveling apart at 0.9 c - everyone still agree ?
0.5 c - they would be traveling apart at c -everyone still agree? speed moving apart = sum of the 2 speeds
now if 1 ship goes 1mph faster its now longer sum of the 2 speeds why what changes with the 1 extra mph ?
q2: if i shine a torch in front of me imagine a phonton thats travelling out of the torch at c if I start walking backwards does the photon slow down to compensate ? and how does it know im walking backwards ?
q3: If iI sneak up behing arwin and shine a torch in the opposite direction he is facing, does that mean he will never be able to walk forward
Yup, almost right.
Nope. They would be travelling at 0.748c
Now they would be traveling at a speed of 0.8 c.
It doesn't slow down. It doesn't know that you are walking.
Since you know that you are walking relative to ground, then you are not in your own frame. You are in the ground's frame. And hence, it doesn't matter whether you are walking or not. And there is no need for photon to slow down.
Look at it this way, if you were moving in a space ship at c/2 and arwin was in another spaceship which was stationary, even then both of you will see the SAME photon traveling at c.
It is completely clear to me that light or indeed most waves travel at a constant speed not related to the speed that emitted them. Movement of the emitter only influences their starting point, and you can focus light into a laser, but once 'released' it just goes as it always does. But the other bit about the speed between the two spaceships I can't see yet.
There is a rather easy way to make "c + c = c", 0, or c - c. I'm not sure if it is correct, or if it helps, but if you inverse the meaning of speed to something in the line of "how much slower than max" (max - act) instead of "how max faster than min" (act - 0) then you can make all kinds of counter-intuitive calculations.
A famous old example of this is the turtle-race (from some greek guy), when you always run to the position the turtle was you can not surpass the turtles position. In that tale the turtle's position is "max" and you are framed in the range [0,max]. And even in that turtle-scenario you slow down (just like time does in the case of speed) all the way to an almost halt. You'll mathematically actually never reach the turtles position, and I guess it's the same with c.
I find it nice as a metaphor to remove the conflict in ones thinking, seeing how can something obvious "wrong" have a very normal explanation.
A famous old example of this is the turtle-race (from some greek guy), when you always run to the position the turtle was you can not surpass the turtles position. In that tale the turtle's position is "max" and you are framed in the range [0,max]. And even in that turtle-scenario you slow down (just like time does in the case of speed) all the way to an almost halt. You'll mathematically actually never reach the turtles position, and I guess it's the same with c.
I find it nice as a metaphor to remove the conflict in ones thinking, seeing how can something obvious "wrong" have a very normal explanation.
That does not work.
https://secure.wikimedia.org/wikipedia/en/wiki/Velocity-addition_formula
That's the best way to understand it.
https://secure.wikimedia.org/wikipedia/en/wiki/Velocity-addition_formula
That's the best way to understand it.
OK I have a visual example that I'd like to offer with a question to follow.
1. Lets say you have a gun that is traveling at the speed of light in the negative direction from + to - on an X axis.
2. At the instant the gun passes the origin "0" it fires a bullet at the speed of light in the positive direction from 0 to + on the X axis.
3. If the bullet were to represent a ray of light, what would an observer standing at point +5 on the X axis see? Would the observer see the gun moving away or standing still? Assume the observer has no frame of reference relative to the gun eg no background or floors etc.
4. What would the observer see if they were moving at the speed of light in the positive direction from +5 to +infinity?
:smile:
1. Lets say you have a gun that is traveling at the speed of light in the negative direction from + to - on an X axis.
2. At the instant the gun passes the origin "0" it fires a bullet at the speed of light in the positive direction from 0 to + on the X axis.
3. If the bullet were to represent a ray of light, what would an observer standing at point +5 on the X axis see? Would the observer see the gun moving away or standing still? Assume the observer has no frame of reference relative to the gun eg no background or floors etc.
4. What would the observer see if they were moving at the speed of light in the positive direction from +5 to +infinity?
:smile:
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I know my maths is pretty bad (but windows calc agrees with me at least)
but why does 0.45 + 0.45 = 0.748 and not 0.90 ?
Dunno whether you're being sarcy or not, but rpg.314 has already posted a link that explains it. Read it.
Because it is a mathematical construct, apparently. The only way to make light a constant was by making everything else relative to it. I personally think that's cheating, but hey.
EDIT: is the speed of light defined as a mathematical 'limit'? Fwiw, if v is the velocity of an object travelling in one direction, and a second object is travelling at the same velocity in the opposite direction, then the velocity at which one object moves itself away from the other is 2v. Any discussion of this happening in terms of light-speed is far too theoretical for me to care about whether or not we need to bend reality to suit calculations in relation to light-speed for it. Which I'm thinking rpg.314 is saying also.
Well when you approach the speed of light It goes like this:
= (0.45c + 0.45c) / (1 + (0.45c)(0.45c)/c^2)
= 0.748c
Because it is a mathematical construct, apparently. The only way to make light a constant was by making everything else relative to it. I personally think that's cheating, but hey.
Fwiw, if v is the velocity of an object travelling in one direction, and a second object is travelling at the same velocity in the opposite direction, then the velocity at which one object moves itself away from the other is 2v. Any discussion of this happening in terms of light-speed is far too theoretical for me to care about whether or not we need to bend reality to suit calculations in relation to light-speed for it. Which I'm thinking rpg.314 is saying also.
Sorry Arwin, but this is utter bunkum. STR is not some kind of "cheat" - it's been experimentally proven. You seem to be saying that because it's counter-intuitive it must somehow be a mathematical trick.
