three speeds at once.

[dstebbins]

Special relativity states that the speed of light is constant for all observers, whether they're traveling at 1 m/s or 99.9% the speed of light, light travels at c, which is approximately 300,000,000 m/s. However, in my tiny little mind, this statement makes about as much sense as "afdjaojvalfjdl;kj!"

 

Suppose for a minute that a spaceship is flying at 150,000,000 m/s relative to a planet. To the planet, the light reflecting off the ship is traveling at 300,000,000 m/s, but to the spaceship, it's traveling at 450,000,000 m/s relative to the planet.

 

So in conclusion that means that the same light, the light being observed by both parties at the same time, is traveling at two speeds at once. That doesn't make a bit of sense. How can an object have more than one speed at one time?

 

I'm sure this has been brought up before in the over a century that this theory has yet to be disproven, but I seem to have been home sick that day. What's the answer?

[YT2095]

but to the spaceship, it's traveling at 450,000,000 m/s relative to the planet.

 

there`s the problem you`re having, you`re mixing frames in one sentence.

 

speed is taken in relation to Single frame at a time, not several at once.

[dstebbins]

You seem to suggest that if you're on the ship, the person on the planet doesn't exist, so his observations don't exist, but they do. How can an observer just disappear?

[YT2095]

they don`t disappear, they just aren`t factored into it, you observe from YOUR frame and look at something (One thing), you can`t look at 2 for a relationship to each other, it just doesn`t work like that.

 

the light leaving the craft no matter what speed it goes will be light speed.

 

the most in way of effect you`ll get will be a color shift, but 300M m/s will remain the same.

[Severian]

The speed of the object isn't an intrinsic property of the object. One can only have speeds relative to something else. So the ship has a 'speed relative to observer 1' and a 'speed relative to observer 2'. These are different quantities, so they don't have to be the same. That is why it is called 'relativity'.

 

(Incidentally, the adding of velocities as you describe is not true in SR, but that is a different issue.)

[Norman Albers]

Think of matter as light which has convinced itself to be more or less at rest. You have a form of energy measuring energy propagating.

[foodchain]

So then, light can go faster then the speed of light? I mean if someone fires a cannon, and I am moving at say 10,000 fps parallel to the round, this is not going to physically change the speed of the round right? It may appear to me differently then someone standing still, but the bullet is still simply doing its speed right? So basically the confusion comes into play because the variables themselves are not changing, such as the speed of the round, its the relationship of objects, such as two different observers of the round?

[YT2095]

if you`re lucky enough to achieve C with a cannon on board and fire it at 10kfps, then to you holding the igniter cord, it will move at 10kfps.

to someone stationary outside the ship as it passed, wouldn`t even see the cannon ball move.

everything hitting the observers eye would still be at light speed.

 

so in order to see it it would be like a 300millionth of a sec shutter speed just to even capture Something, like a still shot.

 

you just wouldn`t see it

and if you did, nothing to YOU as it passed would seem to change.

[Norman Albers]

I read Einstein had a dream about cows against a fence wire. He sat at the far end of the fence while the farmer turned on the electricity to the electric fence. One by one as the voltage propagated down the wire the cows jumped away. The farmer saw them jump one after another at a rate double the SOL divided by separation of cows. What did Einstein see at the far end? No this is not directly relevant, because the characters are stationary to each other, except the cows which presumably manifest transverse motion away from the wire. Foodchain, 10kfps is low compared with the SOL. If, say, [math]\beta=\sqrt{1/2}[/math], then [math]\gamma=\sqrt 2[/math] and you are getting relativistic.

[dstebbins]

The speed of the object isn't an intrinsic property of the object. One can only have speeds relative to something else. So the ship has a 'speed relative to observer 1' and a 'speed relative to observer 2'. These are different quantities, so they don't have to be the same. That is why it is called 'relativity'.

 

But you see, it's this that causes the problem. Relativity speaks that there are two kinds of speeds: Absolute and relative. A material object's velocity in Relativity is relative to an observer, but the absolute velocity is the same, is it not? Light, on the other hand, has a constant relative velocity, so its absolute velocity has to change, but that's impossible.

[YT2095]

perhaps an easier way to think of it is like this...

 

you and your friend are standing next to each other both looking at a clock in the middle of a field, this clock has a second hand as well, and you both see it move at the same time, now at 12:00:00 (for arguments sake) you flee away from that clock at light speed, the clock will stay at exactly 12:00:00 to you, because you`re in that frame of that Time point forever (until you slow down of course and then it starts catching back up with you again).

your friend standing there on his own now will still see time exactly as he did before you went, although if he could see your wrist watch, it also would be stuck at 12:00:00 even though the clock in the field says maybe 10 minutes past

 

the clock itself doesn`t care however it`s just doing it`s thing, but if the clock were to take off in the opposite direction than you you mate in the field would see the time not change (like he saw no change when he looked at your wrist watch) so to him you`ve Both frozen.

 

but to YOU now and the clock is going in the opposite direction at light speed, the time doesn`t change, you notice no difference even though it seems mathematically you`re pulling 2c between you. you`re Not, c is a constant, time won`t go backwards, it will just stay still

you`ll be in exactly the same state as your friend in the field.

 

some of this assumes you have Really good eyesight too

[Severian]

So then, light can go faster then the speed of light? I mean if someone fires a cannon, and I am moving at say 10,000 fps parallel to the round, this is not going to physically change the speed of the round right? It may appear to me differently then someone standing still, but the bullet is still simply doing its speed right? So basically the confusion comes into play because the variables themselves are not changing, such as the speed of the round, its the relationship of objects, such as two different observers of the round?

 

No. Since all speeds are relative, your motion changes the speed of the cannonball you observe, as you say. Indeed, this is present in normal Newtonian mechanics too. The difference is how you compute the change from one observer to another. If the cannonball is doing 10,000fps (fast cannonball!) compared to you, and your friend is moving at 5,000fps relative to you in the same direction as the cannonball, Newtonian mechanics tells us that the cannonball will be doing 5,000fps relative to him.

 

This is not true in relativistic mechanics since velocities don't add linearly. However, the momentum, defined as [math]p=\gamma mv[/math] with [math]\gamma=\frac{1}{\sqrt{1-v^2/c^2}}[/math], does add linearly, so you can still work it out. (In fact, it is because [math]\gamma \approx 1[/math] for slow objects that makes [math]p \propto v[/math] making it look like velocities add linearly in 'real life'.)

 

But you see, it's this that causes the problem. Relativity speaks that there are two kinds of speeds: Absolute and relative. A material object's velocity in Relativity is relative to an observer, but the absolute velocity is the same, is it not? Light, on the other hand, has a constant relative velocity, so its absolute velocity has to change, but that's impossible.

 

No. there is no such thing as absolute speed. Everything is relative.

[someguy]

personally i always thought that this could happen because of the dilatations that occur when you approach the speed of light and they would compensate for the fact you are moving faster towards light for example and so for you, in any reference frame, light would always seem to be moving at the same rate, even if you accelerate greatly towards it.

 

but that would mean as a third observer you could watch a ship moving really fast towards a beam of light and if you combine their speeds moving towards each other the sum would be greater that c since the speed of light compared to you is c.

[YT2095]

only on paper using basic 2+2=4 maths, I can design a machine that will do 17x the the speed of light using 5 large Cog wheels, of course in Reality this could never happen.

 

you hit c and time stops to everything else that isn`t moving that fast.

 

that simple really

[dstebbins]

No. there is no such thing as absolute speed. Everything is relative.

 

I had a feeling you'd say that.

 

Is there really no such thing as absolute speed, or could absolute speed be a manifestation of a relative speed, relative merely to a universal frame? It is common knowledge that energy of motion and energy of heat are the same thing, so when an object reaches a temperature of absolute zero, it is absolutely stationary, therefore, this theoretical object would be the perfect universal frame. The only problem here is that matter as we know it cannot obtain a universal frame.

 

However, the need for a material object to be the universal frame is bull. Who says we can't designate a point in space to be the universal frame? The "origin of the coordinate grid" if I may. Sure, even the vacuum of space has kinetic energy (about 3 degrees kelvin between galaxies), but there's no matter around for the enegy to affect. The vacuum would stay stationary.

 

So in a sense, absolute location (location relavent to the absolute frame) can be measured, and if we can measure absolute location, we can measure absolute speed.

[YT2095]

just Being there in that "Zone" would change it, and so No.

[dstebbins]

What do "zones" have to do with anything? I'm talking about absolute frames.

[YT2095]

it wouldn`t be an "Absolute" if you were in there to observe it.

[Norman Albers]

My apprehension of these things has steadily grown for the last forty years (I have squawked 58 years on the planet). In college as a research assistant I was part of an accelerator physics team, and I did programming of relativistic kinematics, the billiards of high-energy collision. Mesons which have a lifetime of so many nanoseconds or whatever, in their own frame, went whizzing across many feet from the target to our walls of counters, lasting a much longer time in our reference lab frame. Angles were folded forward as per momentum conservation, etc. Then it is also useful to hang out with models like "long trains with a clock in each car", or a "police car with really long antlers with lights", whatever your style. You will see that according to the Lorentz transform rules we know to be so, time and space fold into one another. Now that I am working to develope understanding of fundamental things from inhomogeneous electrodynamics, I really can see matter as basically light caught in circles. I see light and matter as manifestations of the deeper field which presents itself a priori the same to all observers regardless of their mutual velocity. This is relativity, and many questions lie in this realm of unification. dstebbins, careful with CMB analogies. There is at any locale in the large, a unique frame which in which the CMB is perceived isotropically. CMB is not the same as the virtual vacuum.

[YT2095]

then you would also agree that there is no such thing as "Absolute Motion", and thus without that frame nothing can ever be 100% stationary.

[Norman Albers]

Yes there is no place especially to hang our hats, or as Jimi Hendricks sang it, "There must be some way out of here, said the joker to the thief..."

[YT2095]

a Trifle Oblique, but I`ll accept the yes

[Norman Albers]

This is a good attitude with which to approach physical theory.

[dstebbins]

it wouldn`t be an "Absolute" if you were in there to observe it.

 

Woah woah WOAH! I said the absolute frame was a POINT in space! Not a 3D region! You can't be IN a point!

 

And even if you were to rephrase that and say you could be "on" the point, that still doesn't mean anything. It's just like a coordinate point being on the origin of the coordinate grid. It has an absolute location: 0,0,0.

[Norman Albers]

No, no, my light cone centers on myself!!! I am <0,0,0,0>. Riiiight. How do you locate your grid?