# Nothing faster than the speed of light -- Why?

The other thread on flashlights and spaceships and General Relativity got me thinking about something. I don’t know, it sounds like a stupid question, but it’s physics, and those question always sound stupid when I ask them.

So nothing can go faster than the speed of light. Why? I mean, I know what happens when you approach the speed of light – time slowing down and all that – but again, WHY does time slow down? Or asked differently, what causes light to travel at the speed of, well, light?

Well, the simplest way to say it is that anything with any mass will appear to increase in mass as it approaches C. To reach C, its mass would become infinite so you’d need infinite energy to accelerate it to C.

As for WHY it does this, along with time dilation and shrinking in the direction of travel. i’ll let someone else tackle that.

The Snack… I can’t get on the search at this time, but this has been done INTO THE GROUND on this board in the past.

If you want the historical explanation… the speed of light in a vacuum being constant comes from results out of Maxwell’s Equations setting up an electromagnetic wave with velocity of the speed of light in a vacuum. Lorentz factors and nearly all of special relativity can be derived from such considerations. The basic premise of the way relativity works is that it allows for the laws of classical dynamics of systems of particles with mass, momenta, etc. to be consistent with the Maxwell Equations. That is why speed of light in a vacuum is constant.

We can further appeal to Michelson and Morley for a greater discussion, but I’ll let you look that up on your own.

I thought that anti-matter could be propelled at the speed of light? Or am I just an idiot?

Light (photons) has no rest mass, and travel as fast as anything in the universe. That speed limit is c. Antimatter has mass, just like regular matter, and are subject to the same laws - i.e. gets heavier the closer it gets to c, and can never quite reach c.

As for why there is such a limit, that’s not a question physics can answer. The universe just behaves that way, and physics can only describe how the universe works, not why. If you want to know why, try the theology or philosophy department.

yeah, i agree with scr4. i mean, c is the speed of light. all a scientist can say is that that is the limit (or, that c is not the limit, and explain an experiment backing up that assertion).

other than that, well, c is the observed limit. that’s the way our universe works.

however, i am sure that someone more versed than i can explain the relationship between this constant and other constants, and give a context for how c fits into the bigger picture.

jb

Well, here’s a WAG from a dabbler, but by no means specialist…

If you add energy to mass, it goes faster, but to get to c, you have to add infinite energy.
If you add energy to light, it doesn’t go faster, it just increases in frequency (gets brighter, goes from red to blue, etc.). So there is no way to create a particle that goes faster than c (not counting tachyons, which are theoretical particles that, by definition, only move faster than c).

One way to approach the “why” of the matter is to look at the metric, or way of measuring distances, of the space we live in. In flat, 3-d space, if you want the distance between two points, you measure the difference in x, y, and z positions, and distance[sup]2[/sup] = dx[sup]2[/sup] + dy[sup]2[/sup] + dz[sup]2[/sup]. If you change what axes you use for your coordinate system, then x, y, and z might change, but the distance won’t: It’s what’s referred to as an invarient. It turns out that if you add time to the three spatial dimensions, then the invarient distance formula is distance[sup]2[/sup] = dx[sup]2[/sup] + dy[sup]2[/sup] + dz[sup]2[/sup] - dt[sup]2[/sup]. From this non-Euclidean metric (called the Minkowski metric), with a minus sign in front of the time part, you can get all of the results of Special Relativity. If you use more complicated formulas for the metric (but still with the time part negative and the space parts positive), you get General Relativity.

Noticed that this wasn’t covered, so I’ll answer it.

No, antimatter behaves just like everything else in this respect. The difference between a particle and its antiparticle is they have opposite charges. Antimatter still has the same kind of mass as ‘regular’ matter, so it still has inertia. Which keeps you from accelerating it to c.

As to you being an idiot, don’t be so hard on yourself. Most of the people around you don’t even know enough to form the question you asked.

I’m far from a physicist. I think at least 20 miles. But nothing can be accelerated faster than the speed of light, as already explained, because that would require infinite energy. However, if at the creation of the Universe - at the Big Bang - there were matter traveling faster than c (and there is no reason why there couldn’t have been), then in order to get them to move slower than c, it would also require infinite energy. However, we can never acquire any knowledge of them because they move faster than c.

Tachyons…interesting. I wonder if my Universe in a Nutshell by Hawking covers it.

In Special relativity, nothing travels faster than c and light always travels at c. SR assumes an inertial reference frame.

In General Relativity, nothing travels faster than light (in the vicinity), but light doesn’t necessarily travel at c. Particles can travel faster than c, just not faster than light.

You cannot apply SR in the early universe, because any inertial frame would be infinitesimal. (Actually inertial frames are always infinitesimal because you always have some masses present.) So yes you would have particles traveling faster than c, but not faster than light.

I question the very existence of particles that we can never acquire any information of.

Because it’s the law.