# The Naked Scientists Forum

### Author Topic: why can't anything travel faster than the speed of light?  (Read 5183 times)

#### CZARCAR

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##### why can't anything travel faster than the speed of light?
« on: 05/10/2014 09:31:48 »
thank you

#### yor_on

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##### Re: why can't anything travel faster than the speed of light?
« Reply #1 on: 05/10/2014 09:45:51 »
To travel faster than the speed of light in a vacuum you either need something existing, already doing so, or you will need to accelerate something. In the first case nobody has found any experimental proof, although it can exist in theory. In the other case it will take a infinite energy, according to Einstein, to gain that 'ftl' speed, actually not ever reaching 'c'. When someone tells you that light is moving 'faster than light' inside a material you better have a look here. http://www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/node4.html

#### JohnDuffield

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##### Re: why can't anything travel faster than the speed of light?
« Reply #2 on: 05/10/2014 10:21:11 »
Why can't anything travel faster than the speed of light?

Let's limit ourselves to an electron. Why can't the electron travel faster than light? IMHO the answer is lurking there in things like pair production and electron diffraction and the wave nature of matter. The electron can't go faster than light because in a way it is light. See atomic orbitals where you can read this: "The electrons do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves". In simple terms, think of an electron as light going round and round a circular path like this O. Now turn the circle sideways like this |. Now move it fast, and the circle looks like a helix, something like this: /\/\/\/\/\/\/\. Moving the electron fast is a bit like stretching a helical string. You can put in more and more KE=½mv² kinetic energy and stretch it straighter and straighter, but you can't stretch it straighter than straight. And when it's almost straight it isn't going round and round any more, it's like it's a photon going straight. At the speed of light. You can't make an electron go faster than light just as you can't make a photon go faster than light. Because you can't make light can't go faster than light.

#### jeffreyH

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##### Re: why can't anything travel faster than the speed of light?
« Reply #3 on: 05/10/2014 10:52:53 »
Because of time dilation, length contraction and the intensification of spacetime curvature. There is a balance between these that guarantees you cannot go faster than light all linked together via Planck's constant.

#### PmbPhy

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##### Re: why can't anything travel faster than the speed of light?
« Reply #4 on: 05/10/2014 11:18:52 »
Quote from: yor_on
In the other case it will take a infinite energy, according to Einstein, to gain that 'ftl' speed, actually not ever reaching 'c'.
I derived an expression for the relativistic mass of an object here
http://home.comcast.net/~peter.m.brown/sr/inertial_mass.htm

Relativistic mass is the quantity m such that p = mv. That derivation shows that as v -> c, m -> infinity as does the momentum p.

#### lightarrow

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##### Re: why can't anything travel faster than the speed of light?
« Reply #5 on: 05/10/2014 12:26:50 »
thank you
Because to do so, the object's mass should be imaginary, and we have never seen such a thing; furthermore, there is no mostly accepted physical theory who contemplate imaginary mass, at the moment.

--
lightarrow

#### jeffreyH

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##### Re: why can't anything travel faster than the speed of light?
« Reply #6 on: 05/10/2014 12:46:01 »
Quote from: yor_on
In the other case it will take a infinite energy, according to Einstein, to gain that 'ftl' speed, actually not ever reaching 'c'.
I derived an expression for the relativistic mass of an object here
http://home.comcast.net/~peter.m.brown/sr/inertial_mass.htm

Relativistic mass is the quantity m such that p = mv. That derivation shows that as v -> c, m -> infinity as does the momentum p.

I liked the derivation. It actually gives me some insight now that I have stuffed my head full of the math. Once I finished on the Maxwell equations I may come back to you on this.

#### evan_au

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##### Re: why can't anything travel faster than the speed of light?
« Reply #7 on: 06/10/2014 07:09:23 »
There is one restricted scenario where subatomic particles can travel faster than the speed of light in a dense material; this produces the blue glow of Cherenkov radiation often shown in photos of a nuclear reactor.

When people talk about "going faster than the speed of light", they usually imply "going faster than the speed of light in a vacuum".
The speed of light in other materials is lower than the speed of light in a vacuum by a ratio called the refractive index. So in glass, light travels about 60% of its speed in a vacuum, and it is possible to make electrons or protons travel faster than this.

#### JohnDuffield

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##### Re: why can't anything travel faster than the speed of light?
« Reply #8 on: 06/10/2014 12:23:02 »
The speed of light in other materials is lower than the speed of light in a vacuum...
I heard a nice analogy for this. You walk along the pavement at 4mph. But light in glass is like you walking along the pavement with a whole load of people in the way. You still walk at 4mph, but you have to go round people, so you don't cover four miles in one hour. And if you're a little lady with little steps, you are more impeded than a big guy with big strides. You might cover only two miles in one hour. But I can drive my car down the pavement at 3mph, whereupon people get out of my way, and I go faster than you.

#### chiralSPO

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##### Re: why can't anything travel faster than the speed of light?
« Reply #9 on: 06/10/2014 15:48:23 »
I can attest, as a big guy (>190 cm) who takes large steps, I have no advantage maneuvering in a crowd (besides being able to see where I am going.) If anything, taking smaller steps is better in a dense crowd--imagine the average distance between obstacles is less than my average stride--this makes it harder for me than someone who can take several steps between obstacles.

#### UltimateTheory

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##### Re: why can't anything travel faster than the speed of light?
« Reply #10 on: 06/10/2014 16:43:00 »
Couple years ago I made real-time special relativity mass calculator:
http://www.ultimate-theory.com/en/2012/12/26/special-relativity-mass-calculator

You can enter mass of object, and velocity (either with units m/s, km/h or fraction of c), and instantly (while entering) see how relativistic mass, and Lorentz factor is growing..

#### jeffreyH

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##### Re: why can't anything travel faster than the speed of light?
« Reply #11 on: 06/10/2014 23:40:24 »
Couple years ago I made real-time special relativity mass calculator:
http://www.ultimate-theory.com/en/2012/12/26/special-relativity-mass-calculator

You can enter mass of object, and velocity (either with units m/s, km/h or fraction of c), and instantly (while entering) see how relativistic mass, and Lorentz factor is growing..

Very interesting.

#### ScientificSorcerer

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##### Re: why can't anything travel faster than the speed of light?
« Reply #12 on: 07/10/2014 03:52:52 »
you would need some sort of warp drive or be able to make yourself and ship massless. mass is just the interaction from energy with space which causes distortions called gravity.  Theoredically if you could cancel out mass then even the smallest amount of energy could push you to light speed, oddly enough though, you ould probably not go faster then light but time will slow down around you and you will appear to be going faster then light from your perspective.  If you could make your ship less then mass-less (negative mass) you could perhaps go faster then light.

#### The Naked Scientists Forum

##### Re: why can't anything travel faster than the speed of light?
« Reply #12 on: 07/10/2014 03:52:52 »