I don't see how that follows. The Einstein equation just means that a lower mass will have lower energy.
I accept that the maximum velocity would be c, but see no reason why a mass-less entity couldn't have an arbitrary lower velocity.

I think it's because in the absence of any other force stopping it or slowing it down, it will simply travel as fast as possible; which in this case is the speed of light.

 

In the absence of a force to accelerate or decelerate it its speed will be constant. But why necessarily c?

 

In the absence of a force to accelerate or decelerate it its speed will be constant. But why necessarily c?

You can find an answer to why all massless particles travel at the speed of light here: http://van.physics.illinois.edu/qa/listing.php?id=1354

 

Thanks for the link.

 

Eliminating the mass of our sun would release so much energy that our planets would probably be vaporised. So their paths post-elimination is academic .

It's a hypothetical setup. The Sun disappears by magic. No energy is released. The question is about how gravity acts at a distance and the answer is that changes in what we perceive as gravity obey our theories about speed of light limitations.

 

speed of light limitations.

Whats the speed of light limitations ???
It as been proven that unreadable information as of now can travel faster than light ..

 

Since the hypothetical elementary particle that carries gravity (the graviton) would have 0 mass, gravity must travel at the the speed of light.

So light is a massless particle?

Whats the speed of light limitations ???
It as been proven that unreadable information as of now can travel faster than light ..

Probably meaning, fastest known speed. Nothing is faster, and like his example showed how time and speed of light interact.

 

So light is a massless particle?

Hypothetically, if the carrier for the electromagnetic force (the photon) had mass, then light would not be as fast as the speed of light; which would mean that c is a constant in the universe and not the real speed of light -as only massless particles (e.g. the graviton) can travel that fast-. Only if the photon has no mass could light travel at the speed of light.

In any case, it is believed that the photon has 0 mass; though an upper limit as been calculated at: 10^−18 eV/c^2 (equivalent to 1.07×10^−27 atomic mass units)

 

You can find an answer to why all massless particles travel at the speed of light here: http://van.physics.illinois.edu/qa/listing.php?id=1354

Great link

 

Since I posted on this thread that photons are believed to have no mass, I had a doubt on the back of my head:

Einstein predicted that light would be attracted by massive objects (e.g. stars), and later Eddington confirmed it during an eclipse.

But, how can massive objects attract light, if photons have no mass?

The answer seems obvious, but I didn't realize exactly why until yesterday.

 

Whats the speed of light limitations ???
It as been proven that unreadable information as of now can travel faster than light ..

I have heard hosing a wall as a good example. You can create water patterns on the wall which 'move' with greater velocity than any given water molecule from the hose. I recall the use of phase velocity in this somewhere. But as you said, meaningful data, in the form of pulses or such, cannot violate c.
@adam555 thanks for the earlier link. Very informative piece.
Photons, gravity and such is always a bit mind blowing, especially if you take school teachers at face value
D

 

Trying to figure out how light, space and time behave is as amusing as physics gets; I've been doing it since I can remember... until I found out that a guy called Einstein had figured it all out already.

Now the fun is in trying to understand the implications of what Einstein figured out.

 

I have heard hosing a wall as a good example. You can create water patterns on the wall which 'move' with greater velocity than any given water molecule from the hose. I recall the use of phase velocity in this somewhere. But as you said, meaningful data, in the form of pulses or such, cannot violate c.
@adam555 thanks for the earlier link. Very informative piece.
Photons, gravity and such is always a bit mind blowing, especially if you take school teachers at face value
D

The problem is that science is finding out that there findings are incorrect ... Also they did find out that unreadable information can travel alot faster than light so what happened to nothing can travel faster then light ??? Well I guess they where wrong no big surprise there..For me science is one famous person's opinion and some times the right person doesn't receive the credit that they should..

 

The problem is that science is finding out that there findings are incorrect ... Also they did find out that unreadable information can travel alot faster than light so what happened to nothing can travel faster then light ??? Well I guess they where wrong no big surprise there..For me science is one famous person's opinion and some times the right person doesn't receive the credit that they should..

imho i couldn't disagree more. Science as we know it is based on publicly verifiable evidence, even if we can't understand everything
Look at Einstein for example. You might say relativity was his opinion...Then, as said above, Eddington went to verify some of its effects during an eclipse. Is it still merely Einstein's opinion?
Also, Einstein hated QM but his mere fame didn't mean that he was right and QM was wrong.

Always remember that every scientific theory is one good, reliable experiment away from being wrong but no experiment can ever prove it right

Sorry if that sounded like a rant: it is not meant like that at all
Regards,
D

 

Any sufficiently advanced technology is indistinguishable from magic. ... Richard Feynman,

The thing is that so much science today requires a PhD level of understanding. You need to get you head down and do hard maths for years to come to any reasonable sort of understanding.

In a sense Einstein proved Newton wrong, but we still uses Newton's equations for motion because for most practical purposes they are close enough and adding the complexity of relativity simply is not worth it.

Remember that we would not have electronics without quantum physics, I might not be able to derive the equations for electron movement in semi-conductors but it doesn't mean that someone hasn't done that work. And because I have not climbed that particular learning curve does not mean that their work is just opinion - I trust that they got it right and that is why we have efficient semiconductors

 

"Always remember that every scientific theory is one good, reliable experiment away from being wrong; but no experiment can ever prove it right".



I've always been a science freak, but I love Machining; because it is an exact Science.

Way too much theory, is just theory.

 

I love Machining; because it is an exact Science.

Not for me!

Seriously. My brother in law is a machinist. I told him to make an interference fit for me. He built the parts in Kentucky and mailed them to me in Florida. When I opened the package and picked up one of the parts, the other one fell out and hit the concrete floor.

Then there is the part about using equal pressure on the micrometer to measure a piston and the hole it belongs in. Never could get that right.

 

Not for me!

Seriously. My brother in law is a machinist. I told him to make an interference fit for me. He built the parts in Kentucky and mailed them to me in Florida. When I opened the package and picked up one of the parts, the other one fell out and hit the concrete floor.

Then there is the part about using equal pressure on the micrometer to measure a piston and the hole it belongs in. Never could get that right.

I learned that "Machinist Feel" PDQ, when representatives from Aerospace industry came around. Sometimes, they would come monthly, and make sure our instruments were calibrated properly.
Like we didn't know how.....

What Class of interference fit, did you request? Dimensions?

 

I can't remember the dimensions. That was at least 10 years ago. Probably about a 1.5 inch bearing in a 1.499 inch hole. Point being, no slop in the bearing fit. Enough pressure to keep it from spinning in the hole. I assumed a machinist would know how tight to make it because he had the bearing in his hand.