Light at Light Speed

[KilljoyKlown]

Gravity is related to position, and so gravity-based time dilation is asymmetric in that both parties agree the person closer to the gravitational mass is the one with the slower clock. Thus time really does seem to vary with position, and this is why gravity is modeled as curved space-time. While local and small experiments don't detect this effect, over larger distances it is obvious that here is different than there.

I don't believe agreement has anything to do with it, as we can measure the difference in time with great accuracy. Example our GPS satellites have to be time adjusted or their position calculations would be a lot more imprecise.

 

[Motor Daddy]

James, you seem to fail to remember that you left the conversation, you didn't prove me wrong. As a matter of fact I went on to prove that I can measure the velocity of a box in space from inside the box, mathematically.

Also, I refuted Einstein's chapter 9 thought experiment with numbers, remember? No? Oh that's right, you had already left the conversation. Well here it is again, in black and white ready for your refutation:

Let's look at Einstein's train thought experiment in Chapter 9. The Relativity of Simultaneity. Einstein, Albert. 1920. Relativity: The Special and General Theory.

Einstein conveniently forgot to put numbers to the thought experiment, so let's do it for him, shall we?

The observer on the train measures the time it takes light to go from the rear of the train car to the front of the train car, which is 11.9915 meters in length in the train frame. Light takes .00000004 seconds to travel the length of the train. That means the absolute velocity of the train is 4,958 m/s.

The observer on the tracks measures the time it takes light to travel the distance between two clocks on the track, which is 1 meter. It takes light .0000000033356409519815204957557671447492 seconds to travel the distance, which means the track has an absolute zero velocity.

It is 10 meters from A to B on the train in the train frame, and 10 meters from A to B on the embankment in the embankment frame. Both observers are at the midpoint between A and B in their respective frames.

Lightening strikes A and B as the two points on the train coincide with the two points on the embankment.

Light takes .000000016678204759907602478778835723746 seconds for each light from A and B to strike the embankment observer. The embankment observer was struck simultaneously from each light at precisely .000000016678204759907602478778835723746 seconds after 12:00:00. That means the strikes occurred at A and B at exactly 12:00:00.

It takes .00000001667792893852027063502108370407 seconds for light to travel from B on the train to the train observer at the midpoint. It takes .000000016678480590418212900804736688488 seconds for light to travel from A on the train to the midpoint observer on the train.

So, the train observer had the light from B impact him .00000000000055165189794226578365298441767877 seconds before the light from A impacted him.

Since the light from B impacted the train observer .00000001667792893852027063502108370407 seconds after 12:00:00 and it took light .00000001667792893852027063502108370407 seconds to travel from B to his midpoint position, the train observer concludes the strike occurred at B at exactly 12:00:00. Since the light from A impacted the train observer .000000016678480590418212900804736688488 seconds after 12:00:00 and it took light .000000016678480590418212900804736688488 seconds to travel from A to his midpoint position, the train observer concludes the strike occurred at A at exactly 12:00:00.

So both observers acknowledge that the strikes occurred at exactly 12:00:00 at A and B. The embankment observer had both lights hit him simultaneously, and the train observer had the lights hit him at different times due to his 4,958 m/s velocity.

Absolute simultaneity!!!

Have at it. I look forward to your response.

 

[Emil]

Forgive me if I'm naive, because I truly am an amateur at science.

I was thinking about light and how it behaves. It seems to me that if we had an imaginary light bulb that was traveling through space at the speed of light, the characteristics of the light generated by the bulb would be altered by the speed of the bulb. Hence, the light waves behind the bulb would be stationary in space as the bulb left a trail of them behind it. And no waves would be generated in front of the bulb since the bulb is moving at the speed of light--we wouldn't see it coming at us until it was right on us. The only vantage point where the light waves are behaving normally is from a side view. I imagine it as being a triangle.

Now, this is just speculation on my part. If anybody can give a better perspective of how light behaves at the speed of light, I would really appreciate your thoughts. :shrug:

To get a much clearer picture, I propose you to think about sound propagation.
Speed ​​of sound depends on the speed of the object that emits sound?

 

[rpenner]

I don't believe agreement has anything to do with it

Agreement here means all observers in the universe agree that a stationary clock at high altitude ticks faster than the same (type of) clock at low altitude. This is seen in the GPS system (compounded with special relativistic effects) and the Pound-Rebka experiment with gamma rays.

Motion doesn't matter in special relativity, only relative motion. But in GR position matters because of the effect matter has on space-time.

 

[Emil]

Agreement here means all observers in the universe agree that a stationary clock at high altitude ticks faster than the same (type of) clock at low altitude.

If I use a mechanical gyro for measuring time, it will spin faster at higher attitude?

 

[KilljoyKlown]

Agreement here means all observers in the universe agree that a stationary clock at high altitude ticks faster than the same (type of) clock at low altitude. This is seen in the GPS system (compounded with special relativistic effects) and the Pound-Rebka experiment with gamma rays.

Motion doesn't matter in special relativity, only relative motion. But in GR position matters because of the effect matter has on space-time.

Now your talking about the concept of spacetime as if time can't be separate from space. When we measure the difference in time, do to it's distance from a gravity source, what does space have to do with it other than the distance from the gravity source?

I've often wondered if time could exist without motion, and I have to think it can't. For without motion of some kind there would be no way to measure the passage of time. But then absolutely everything in our universe is in motion all the time at many levels from the subatomic all the way up to galaxies. The motion of all matter and energy never stops and if it did there wouldn't be any time.

 

[Bowser]

To get a much clearer picture, I propose you to think about sound propagation.
Speed ​​of sound depends on the speed of the object that emits sound?

Eh? I thought an airplane can overtake it's own sound waves when flying supersonic. Hence, the sonic boom when one flies overhead.

 

[Pete]

James, you seem to fail to remember that you left the conversation, you didn't prove me wrong.

You were proved wrong many times by many people. They got bored and left you to crank away to yourself.

As a matter of fact I went on to prove that I can measure the velocity of a box in space from inside the box, mathematically.

Yes, that's a very simple exercise in the mathematical world of euclidian spacetime.
It's also a simple exercise to prove that the same measurement in the mathematical world of minkowski spacetime will always give a result of zero (you should try it).

But what about real measurements?
Back in the [post=2662612]Relativity of Simultaneity[/post] thread, you said you'd leave the actual measurements to the experts. Well, when the experts actually do the measurement they always get a result of zero.

You skipped that issue and left the thread.

 

[Emil]

Eh? I thought an airplane can overtake it's own sound waves when flying supersonic. Hence, the sonic boom when one flies overhead.

Yes, that's correct.

 

[Bowser]

Yes, that's correct.

Actually, I stand corrected. After reading a little about the subject, I discovered that the sonic boom is caused by compression waves that are created by the aircraft itself. They move at the speed of sound.

But getting back to your original statement. How do we compare sound waves to light waves? Do both travel at fixed velocities? What is your correlation?

 

[James R]

Bowser:

How do we compare sound waves to light waves? Do both travel at fixed velocities? What is your correlation?

A big difference is that sound requires a medium to travel in whereas light can travel in a vacuum. The speed of sound depends on the properties of the material the waves are travelling in. Even in air, the speed of sound varies a bit with temperature and pressure. The speed of sound in water is faster than in air. The speed of sound in metal is faster still.

There's no law of physics that prevents a material object from moving faster than sound in a particular medium. Therefore, a plane can outrun its sound waves, which produces the sonic boom.

In fact, a similar thing happens with light, because the speed of light changes in a medium too. For example, the speed of light in water is about 3/4 of its speed in vacuum. The speed of light in glass is about 2/3 of its vacuum speed. In a medium it is possible for objects to move faster than the speed of light in that medium. For example, a cosmic ray particle may land in water with a speed faster than the speed of light in water. When that happens, the particle can create a kind of "light boom", which releases light known as Cherenkov radiation.

No material object can ever move faster than light in a vacuum, and that's the situation we ordinarily consider when we're discussing Einstein's relativity.

 

[Emil]

But getting back to your original statement. How do we compare sound waves to light waves? What is your correlation?

It was just an example that we can understand what is happening in front of the plane and behind the plane in different situations. (We know exactly how sound propagates less about light.)

Do both travel at fixed velocities?

Yes, depends on the medium and not on the speed of the source.
And of course the sound does not propagates in space without air, is not true for the light.

 

[Bowser]

Thanks for your input, James. I really do appreciate your thoughts.

There's no law of physics that prevents a material object from moving faster than sound in a particular medium. Therefore, a plane can outrun its sound waves, which produces the sonic boom.

You might have to revise your theory on sonic booms as I have.
http://en.wikipedia.org/wiki/Sonic_boom

No material object can ever move faster than light in a vacuum, and that's the situation we ordinarily consider when we're discussing Einstein's relativity.

My understanding is that the speed of light is a constant, a measuring stick against which other things are compared. I did come across an article where someone had produced radio waves that move faster than the speed of light.

http://www.universetoday.com/33752/device-makes-radio-waves-travel-faster-than-light/

I find the subject of light to be fascinating. For some reason it's been occupying my thoughts for the past several days, ever since watching Carl Sagan's "Cosmos" on NetFlix. By the way, what the hell is a photon--particle or wave?

 

[Bowser]

It was just an example that we can understand what is happening in front of the plane and behind the plane in different situations. (We know exactly how sound propagates less about light.)

Yes, depends on the medium and not on the speed of the source.
And of course the sound does not propagates in space without air, is not true for the light.

Alright. Thanks for your contribution, Emil.

 

[Emil]

I also thought a very interesting experiment, from the viewpoint of mine.
In a straight line equidistant sound sources are located.
The first sounds a tone, when the sound reaches the second source, which in turn emits a sound. Now the two sounds reach to the third source, it also emits a sound, and so on.
How it will be the final sound?
We return to the object that moves at the speed of sound.
The component of sound which propagates in the same direction as the object remains in the same position towards the object.
So the sound now emitted overlaps with the sound previously emitted.
The result should be similar, as to the previous experiment, if the sound sources are located to very short distances.
And we get to the final question, what happens if a light source moves at light speed.
In front of the light source, the light "gathering" as if the sound?

 

[Bowser]

And we get to the final question, what happens if a light source moves at light speed.
In front of the light source, the light "gathering" as if the sound?

It prompts more questions in my mind. I would imagine it as being a flash of bright light, but what do I know. I suppose I should do a Google on wave theory. That would probably be helpful.

http://en.wikipedia.org/wiki/Wave

Thanks again for your thoughts, Emil.

 

[rpenner]

Now your talking about the concept of spacetime as if time can't be separate from space.

That's because of Minkowski in 1908 showing that Lorentz invariance, the fundamental symmetry of Nature preserved by the Lorentz transforms of Special Relativity leads to a geometry where space and time are not just measured in the same units but can bet transformed into each other via hyperbolic rotations, analogous to ordinary rotations.

When we measure the difference in time, do to it's distance from a gravity source, what does space have to do with it other than the distance from the gravity source?

1) The fact that we have local Lorentz invariance, so one observer's space may be part of another observers time.
2) The meaning of Einstein's equation at the heart of General Relativity.

I've often wondered if time could exist without motion, and I have to think it can't. For without motion of some kind there would be no way to measure the passage of time.

That's like saying that you can't measure air without the motion of wind. But when there is no wind does not imply there is no air.

But then absolutely everything in our universe is in motion all the time at many levels from the subatomic all the way up to galaxies. The motion of all matter and energy never stops and if it did there wouldn't be any time.

E = hf does make it hard to imagine a universe without time even if there is no motion.

 

[KilljoyKlown]

That's like saying that you can't measure air without the motion of wind. But when there is no wind does not imply there is no air.

That example doesn't make any sense as they are not even remotely comparable.

E = hf does make it hard to imagine a universe without time even if there is no motion.

It's no more possible to have a universe without any motion than it is to have a universe with out time. Your equation wouldn't apply if either one of those conditions existed as the laws of nature as we know them could not exist.

 

[rpenner]

Then we must agree to disagree.

 

[jamesbrentonk]

jamesbrenttonk:



Err... wake up and join reality! You're not making sense.



You need to leave this thread. It's obviously way beyond you.



Take it to the Religion forum.



Continue this kind of idiocy and you'll quickly be labelled a troll.



If light had no speed, then when you switched on a light you'd never see the light. You couldn't see the Sun because no light could ever travel from the Sun to your eyes. Wake up and get some common sense. It sounds like you're off your medication.

Sun does not give off rays of light- the ozone gives light naturally.

That could be a very good interpreation.

Also, "lights" don't travel either.

Finally , if you ever suggest thatl ight travels, and you can g rab it touch it and a ny other, then you would actually be invalidating why it would ever move at light speed or move at all to begin with.

You could really s hut down this entire forum for even starting this thread.