Highest velocity possible

Originally posted by PinkFloyd
Just a question-- a Jeopardy! question last week said that physicists had discovered proof of a "tau neutrino". Did I once read that neutrinos move at speeds faster than light? Or am I just mixed-up as usual?

They move at the speed of light if I remember correctly, though wikipedia says they are slightly slower than light.

Originally posted by PinkFloyd
Just a question-- a Jeopardy! question last week said that physicists had discovered proof of a "tau neutrino". Did I once read that neutrinos move at speeds faster than light? Or am I just mixed-up as usual?

Only massless particles can go by the speed of light. No known particles can move with a speed faster than light. Yes, tachyons, byt they are just hypothetical particles, they are not observed, nor prooved existence.)

If the tau neutrino has mass, then they cant go even at the speed of light. Does it have mass? I don't remember...

Originally posted by FabianFnas
Only massless particles can go by the speed of light. No known particles can move with a speed faster than light. Yes, tachyons, byt they are just hypothetical particles, they are not observed, nor prooved existence.)

If the tau neutrino has mass, then they cant go even at the speed of light. Does it have mass? I don't remember...

The latest word is they have mass but so low as to be next to nothing, but having any mass at all means they cannot go exactly at C, close but no cigar.
Lorenz contraction and time dilation has been proven, cosmic rays slamming into the upper atmosphere produces particles with such short rest mass lifetimes they would never make it to the ground but they in fact to reach the ground, proving that time was slowed down for that particle, enough to reach the surface of the earth whereas if they were not relativistic, they would transform into other particles long before they reach the ground.

Originally posted by FabianFnas
Only massless particles can go by the speed of light. No known particles can move with a speed faster than light. Yes, tachyons, byt they are just hypothetical particles, they are not observed, nor prooved existence.)

If the tau neutrino has mass, then they cant go even at the speed of light. Does it have mass? I don't remember...

Tachyons are funny.

They have imaginary mass, for example.

(Still purely hypothetical)

I believe that there is a hole in the "cant travel the speed of light" thing.

It is my understanding that C is a constant. Meaning that if you are in a spacecraft traveling at 90% of C and a beam of light passes you, you will measure its speed as 100% of C (186500 mps), not 10% as you would expect by subtracting your current speed from it. I will dig up references for this if needed.

Following that logic, C will never, ever be attainable. However... could we, in the future, travel 186,500 mps? I believe so. But could we ever catch a light beam? Never.

A very important point is that there are no absolute velocities, all velocities are relative.

"The speed of light in a vacuum is constant" actually means that there is NO frame of reference from which u can every observe light travelling faster of slower then its speed in a vacuum. This is why if you travel at 90% the speed of light (relative to Earth or some other arbitray object) you can shine a torch and the light beam will travel away from you at the speed of light, NOT 10% of the speed of light. BUT, an observer on Earth would see the beam of light travel at the same speed relative to them. In fact, all observers, whatever their velocity would all observe the light travelling at the normal speed of light.

Time and distance alter in the different frames of referance to allow this to be true, which leads to lorentze contraction and time dilation etc...

In short, the maximum speed of anything in the universe is the speed of light in a vacuum. But you must measure the speed relative to something else, and that is what the theory of relativity is all about.

Just to be a bit clearer:

If Observer A measures an object to be moving at a velocity V1 relative to Frame of Referance A, it is possible for Observer B, who is moving relative to Observer A, to measure the object's velocity to be a difference value, V2, relative to Frame of Referance B.

However, if a beam of light is observed, both observers will measure it's velocity to be the same, even if Frame A and Frame B are moving relative to each other.

This is what "the speed of light in a vacuum is constant" means.

Originally posted by MattP
In short, the maximum speed of anything in the universe is the speed of light in a vacuum.

MattP, you have both skill of science, and skill of explaining things. 🙂

In the very first posting of this thread, I wrote: "What is the highest possible velocity in normal space and with things with mass? I say there is no highest velocity at all, what do you say?"

What is your answer for those questions?

Thank you Fabian :-)

In answer to your questions:

The faster possible velocity of anything in the universe is the speed of light in a vacuum, C. Any two frames of reference can never be moving relative to each other with a velocity greater then C, so C really is the faster possible velocity.

However, only massless things can travel at C, such as photons, which make up light. Objects with mass can never reach C, as the energy required to produce a given increase in velocity increases as velocity increases. As the velocity of an object with mass increases, so does it's mass. This is not noticeable at "everyday speeds", but is in particle accelerators and cosmic radiation. As the speed of light is approached, the object has such a large mass that any further acceleration required HUGE amounts of energy.

In fact, a massive object's velocity has an asymptote at C, no matter how much more energy you give the object it's velocity will tend towards, but NEVER REACH C.

These effects have been observed numerous times and are fairly well understood.

Originally posted by MattP
However, only massless things can travel at C, such as photons, which make up light.

If a photon is moving away from me at velocity C then am I not moving away from it at velocity C or is that not the case because of the time dilation experienced by the photon?

Originally posted by twhitehead
If a photon is moving away from me at velocity C then am I not moving away from it at velocity C or is that not the case because of the time dilation experienced by the photon?

If a photon is moving away from you with a velocity of C (relative to you), then you will observe it moving with a velocity of C. If an "observer" on the photon looked at you, he/she would see you moving away in the other direction with a velocity of C.

However, if you then fired some rockets and accelerated away from the photon at, say, 0.5C, the observer on the photon would still observe you to be travelling at C, NOT (1+0.5)C. This is the tricky bit.

Similarly, if were travelling at 0.5C and shone a torch infront of you, you would observe the light travelling away from yourself at a speed of C, NOT 0.5C.

As for time dilation and Lorentz contraction, these are effects observed in inertial frames where things are moving very fast relative to the frames. For example, if you remain in an inertial frame of reference and a very long spaceship moves past you at close to C, say 0.7C. If you measure the spaceship from your frame you will obtain a different length to that obtained by a passenger on the spaceship, who is in the frame of the spaceship. This is due to Lorentz contraction.

Imagine you have two identical clocks which are exactly synchronised and clock A remains with you, stationary with respect to your rest frame, and clock B is put in a spaceship which travels close to the speed of light, relative to you. If you wait an hour in your frame, then compare the time on the clocks, your clock will have progressed an hour (obviously), but the clock on the spaceship will not have moved on very much at all. This is due to time dilation.

In short, Lorentz contraction and time dilation are effects which happen when transforming from space and time coordinates in one frame of reference to another.

I watched "Jose Magueijo's Big Bang" last night on one of the science channels, and learned that this Variable Spped of Light theory is an alternative to something called Inflation theory. It seems that both are trying to address a "fatal flaw" in the Big Bang theory. As I understand it, all the stuff in the universe should be randomly distributed as a result of the BB, but it's not. (why this causes problems for BigBang-ists, I do not understand). Anyway, to get back to this thread, the Variable Speed of Light thing says that 'c' was not always the speed it is today; early in our universe's history, the speed of light was greater--MUCH greater according to Jose. Somehow, this neatly fixes the fatal flaw and "keeps all the good bits" about the BB theory intact.
I should have watched the Twilight Zone; it was the one where Mickey Rooney played a jockey..... 🙄

Originally posted by PinkFloyd
I watched "Jose Magueijo's Big Bang" last night on one of the science channels, and learned that this Variable Spped of Light theory is an alternative to something called Inflation theory. It seems that both are trying to address a "fatal flaw" in the Big Bang theory. As I understand it, all the stuff in the universe should be randomly distributed as a r ...[text shortened]... watched the Twilight Zone; it was the one where Mickey Rooney played a jockey..... 🙄

The BigBang theory holds pretty well. It answers more questions than any other competing theory does.

Originally posted by serigado
You might want to read about tachyons -> theoretical particles that might be going faster then the speed of light.

Sweet! This is like a Star Trek episode. Captain! I think we can use a
tachyon beam. If we can sustain the correct modulation we should be able
to tear up a whole in the space-time continuum and pass through back to
our own time!

Captain: Make it so. And report back to me when you're ready. But hurry.
We've got but five hours before the bubble collapses and crushes the hull
all together!

I love it! 😀

I have nothing of value to add though. 😕