1. Oct 17, 2006

### vivekhere

hi,

Is it so if a particle travels in a speed of light then its mass is considered as Zero????

2. Oct 17, 2006

### Chaos' lil bro Order

Depends on what you mean by a particle. Only photons can travel at the speed of light because they have no mass. Any 'particle' than has mass, like electrons, neutrons, protons, etc. can only approach the speed of light, but they can never reach it. Particle accelerators can speed up electrons to something like 99.9999% the speed of light, but no matter how hard they try, it is impossible to reach 100% of the speed of light.

If you want to know why this is mathematically, I'd suggest you type into google, 'Gamma Function'.

Maybe someone who is good at LATEX can show you hear, just ask.

3. Oct 17, 2006

### LURCH

Like the bro said, particles with mass (rest mass) cannot accelerate to light speed, because their mass continually increases and so it takes more and more force to accelerate them untill finally, at very near lightspeed, the mass of even a single atom would become so great that all the energy in the universe couldn't accelerate it any usefull amount.

Therefore (theoretically, at least), the only particles that can travel at lightspeed are those that have no mass, like photons. So, if we observe a particle travelling at lightspeed, we can know that its mass must be zero.

4. Oct 17, 2006

### vivekhere

Hi,

I have another doubt.

As u all said only the massless objects can travel in the spped of light then there is one theory which states if a matter travels more than a speed of light can be in its future.

can u tell me how this is satiesfied?????

5. Oct 18, 2006

### Chaos' lil bro Order

I'm sorry can you reword that question, I don't understand it.

6. Oct 18, 2006

### Leopold Infeld

He must be talking about time travel...

Its not exactly time travel, its just that when u travel near the speed of light, ur time slows down relative to those who are not travelling at the speed of light. In fact anything moving at a faster speed than some other thing has time dilation. I have heard of something also like astronaut's watches being different after they come back from space etc. So, its the twin's paradox thing that if u go somewhere with the speed of light and come back, u would have only aged for the period of the journey while 80 odd years might have passed on earth..

This is best if u go google things like relativity or gamma function or lorentz transform or just buy some book like A Brief History of Time or Relativity for the Layman etc etc....

oh yeah, there are some obscure things which are way beyond what i know..
like yesterday I read this thing in New Scientist that what u do now could affect what u did yesterday etc etc...tell me if u want to read the entire article or rather here it is

http://www.newscientist.com/channel/fundamentals/mg19125710.900-whats-done-is-done-or-is-it.html

u need to subscribe but if u dont want to, tell me and i could pm it to u

ok ok , i think i said quite a lot of useless and inaccurate stuff.. lol

7. Oct 18, 2006

### vivekhere

hi,

ofcourse i understand that. but i want to ask another thing how a particle in earth can travel in lesser speed than other particle.

8. Oct 18, 2006

### HallsofIvy

Staff Emeritus
There is no such theory. It is true that the Lorentze transformation equations give a negative time (which might be considered moving back in time) if you put speed v greater than c, but there is no evidence that that has any physical significance.

9. Oct 18, 2006

### HallsofIvy

Staff Emeritus
??? Stand beside a road and watch one car pass another! Am I misunderstanding your question?

10. Oct 18, 2006

### vivekhere

hi,

but as posted in New Scientist journel how can a incident we performing in present can effect the past?.

can u explain???

Last edited: Oct 18, 2006
11. Oct 18, 2006

### Staff: Mentor

12. Oct 18, 2006

### Chaos' lil bro Order

vive

Cut and paste the article so we can understand what you are saying. Your English is tough to get.

13. Feb 17, 2007

### jim30

Maybe you are talkin bout Entanglement?...where the effects of 1 Partical can Instantanously be felt by up to two more no matter how far apart they are?