relativity and speed of light for dummies

[3dilettante]

When talking about the speed of light are we referring to visible light? Wouldn't X-rays and gamma rays travel faster than Visible or UV light?

Nope, the speed of light is a constant for all forms of massless radiation. Higher energy radiation doesn't go faster, it has a shorter wavelength.

I think there are a few fringe theories on the nature of time that postulate that high-frequency gamma rays may arrive faster than lower-frequency ones, but those are far from as well substantiated as the one constant to rule them all.

 

[pcchen]

Note that the speed of light in non-vacuum depends on the wave length, like the rainbow thing. However, the speed of light is constant in vacuum.
An interesting effect is, since light travels slower in water, it's possible for some particles to travel faster than light in water (as long as it travels slower than "real" speed of light), such as electrons in a nuclear reactor. When this happens, a similar effect to sonic boom happens and you can see strange glow (called Cherenkov radiation). That's why nuclear reactors always look blue.

 

[StefanS]

Even if you managed to acheive light speed, and time stopped for yourself, time would still continue for the rest of the universe. Thus, by the time you reach your destination, things will have changed, perhaps fatally so.

Actually, that's one of the common misconceptions. Time doesn't "stop". The special theory of relavity deals with two respective system at uniform speed. So it's about the relativity of observation. Time doesn't actually stop, but for an unmoving observer watching you, travelling at the speed of light, it seems as if time has stopped for you. . But the so-called einherent time (aka eigenzeit) doesn't stop.

 

[dizietsma]

My 4 year old daugther can do all these things at or beyond the speed of light

1) Make a mess
2) Eat an icecream
3) Wipe her nose on your shirt when you are not looking

 

[nAo]

My 4 year old daugther can do all these things at or beyond the speed of light

1) Make a mess
2) Eat an icecream
3) Wipe her nose on your shirt when you are not looking

It's a well known fact that babies can easily defy any law of physics

 

[Simon F]

Even if you managed to acheive light speed, and time stopped for yourself, time would still continue for the rest of the universe. Thus, by the time you reach your destination, things will have changed, perhaps fatally so.

Which leads us to the Queen song "39" from "A Night at the Opera" which discusses those very problems.

 

[sytaylor]

I still quite don't get why no object can't travel faster than light.

A nice and straightforward explanation should be very interesting.

E = mc^2

Or reversing the equation, matter is energy but reeeeeeeeeeally condensed. Energy can be transformed to matter, and matter back to energy by colliding certain particles at around the speed of light. So in other words, you would break apart and become energy.

 

[London Geezer]

E = mc^2

Or reversing the equation, matter is energy but reeeeeeeeeeally condensed. Energy can be transformed to matter, and matter back to energy by colliding certain particles at around the speed of light. So in other words, you would break apart and become energy.

... become a LOT of energy actually.

I'm quite sure that if around 80Kg of matter (i'm taking 80Kg as a kind of average weight on this website. I'm obviously WAY below the average!) was to be turned into energy, that would be one hell of a nuclear explosion.

 

[Jabbah]

What is the reference point for the speed of light - or to put it another way how do you know your not moving? Whilst we sit at our computers we dont feel like we are moving yet we are spinning with the earth and rotating round the sun and shooting through the universe.

Lets say you were out in deep space (outside the universe) far enough away from anything so that there was no point of reference for speed - no particles or fields etc. So at this point you dont even know if you are moving. Now drop a beacon and travel away from it at 0.5C now send another beacon out at an additional 0.5C in the direction of travel so its travelling at the speed of light away from the first beacon. Repeat and observe. Whats going to stop beacons travelling away from each other at twice the speed of light after a couple of repeats (ie one of them must be travelling faster than the speed of light)?

 

[sytaylor]

A few mere atoms could be explosive.

I'm way over 85kg but its muscle, not mcdonalds flab

 

[StefanS]

E = mc^2

Or reversing the equation, matter is energy but reeeeeeeeeeally condensed. Energy can be transformed to matter, and matter back to energy by colliding certain particles at around the speed of light. So in other words, you would break apart and become energy.

Unless m denotes dynamic mass which is more or less a crutch, anyway, that's nonsense...

So
E=m*c^2/sqrt(1-v^2/c^2)
or
E_kinetic=m*c^2*(1/sqrt(1-v^2/c^2)-1).

m denoting the rest mass.

As you can see, for v approaching c the relativistic energy diverges against infinity. Thus, you'd need an infinite amount of energy to accelerate to infinity.

 

[hey69]

why should time stop at light speed?

light speed is still a speed and not the infinite speed.

 

[sytaylor]

^ What he said.

 

[StefanS]

What is the reference point for the speed of light - or to put it another way how do you know your not moving? Whilst we sit at our computers we dont feel like we are moving yet we are spinning with the earth and rotating round the sun and shooting through the universe.

The is no reference point. the speed of light is absolute, it's a fundamental constant.

 

[StefanS]

why should time stop at light speed?

See here

 

[hey69]

yeah basicly what I thought.. they write that so crypticly

 

[K.I.L.E.R]

I'm still waiting for Chalnoth to give out an interesting technical answer.

 

[Sc4freak]

... become a LOT of energy actually.

I'm quite sure that if around 80Kg of matter (i'm taking 80Kg as a kind of average weight on this website. I'm obviously WAY below the average!) was to be turned into energy, that would be one hell of a nuclear explosion.

The only way you'd achieve 100% conversion from matter to energy is via. an antimatter-matter reaction. And even then, the majority of energy released is in the form of neutrinos, which passes through matter.

A kilogram of antimatter produces the same amount of energy as a 43 megaton nuclear weapon, an 80kg mass would produce an amount of energy equivalent to a 3.4 gigaton nuclear weapon. Probably enough to blow Earth out of orbit, even though the majority of the energy is wasted.

And the time-dialation effect is also seen under heavy graviational fields - such as those produced by a black hole. Fall into a black hole, and time will slow down for you, although you will observe everything else to be moving faster. Until time effectively stops for you and you get to witness an infinite time passing by in an instant

 

[K.I.L.E.R]

What are you saying?
Black holes wont rip you into pieces? You could technically survive being in a black hole's event horizon or even in it's singularity?

 

[Sc4freak]

Practically, with today's technology, of course not. I'm just stating that theoretically if you somehow survived the gravitational forces, you would eventually see all of time pass until the universe ends.

I guess if you managed to build a ship of neutronium, held together with the strong nuclear binding force, and installed a camera to beam you up video, it might survive. Although it will never enter the event horizon (from our perspective, it would just keep getting slower and slower until it effectively stops just outside the event horizon). And even we did eventually see it fall beyond the event horizon, you wouldn't be able to recieve the transmission anyway, unless you made a beam of tachyons (dunno how that would work).