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cockswain's avatar

How do we know there is nothing faster than the speed of light?

Asked by cockswain (15249points) March 20th, 2010

I know this is a cornerstone of physics, but I’m a layman. Is it not possible for something to be faster than light, or we just haven’t found anything?

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81 Answers

chels's avatar

Because we haven’t found it yet.

Ivan's avatar

We don’t. It’s an implication of Maxwell’s equations, and we derive all our relativistic equations around that postulate.

Parrappa's avatar

It would require infinite mass, which is impossible. I think.

dpworkin's avatar

The LHC proves it every day now. As an object approaches the speed of light, its mass increases. The closer it gets, the larger the mass, the larger the mass the more trouble it has going any faster. Lather, rinse, repeat.

Ivan's avatar

Right, it would take an infinite amount of energy to accelerate something to the speed of light.

cockswain's avatar

Then light has zero mass?

Ivan's avatar

@cockswain

In a sense, yes, it only has energy, although the distinction between energy and mass isn’t as pronounced as you might think.

cockswain's avatar

@Ivan I’ve heard of anti-matter too, but know nothing of the physics of that either. Do you know if ant-matter could theoretically be faster than light? Or is that not a rational question?

Ivan's avatar

@cockswain That’s outside my realm of expertise, as of the moment. My layman’s understanding of anti-matter leads me to believe that it obeys all of the same physical principles as matter, but someone might correct me on that.

dpworkin's avatar

Yeah, think of it as a mirror image. There are no special rules for it.

cockswain's avatar

@dpworkin “There are no special rules for it.”

Could you please justify that statement?

cockswain's avatar

@dpworkin Sorry, my question looks rude. I just mean, are you saying anti-matter must obey the same rules of physics that “normal” matter does?

dpworkin's avatar

So far, in the Standard Model, that’s the way it appears to be.

CyanoticWasp's avatar

We assume not, because if there was, we’d never be able to see it anyway.

talljasperman's avatar

lint travels faster than the speed of light…whats in your pockets just after you do laundry… “lint”....SpaceBalls

CMaz's avatar

Superman is faster then a speeding bullet.

Rarebear's avatar

I think I can help here. Antimatter is the same as matter, just with opposite charge. It obeys the same physics and is subject to the same laws. Protons have positive charge, and antiprotons have negative charge. Electrons have negative charge and positrons (or anti-electrons) have positive charge. In both, gravity is positive (i.e., not antigravity), so an antimatter planet of the same mass as a matter planet, would have the same gravitational field assuming the same density.

In terms of tachyons, they are theorized, but have never been seen.

Note that in Einstein’s equations, and Relativity, there is absolutely nothing that speaks against things moving faster than light. The problem is that in order to ACCELERATE to the speed of light, you’d need infinite energy. But if a particle STARTS faster than the speed of light, as long as it doesn’t decelerate to the speed of light, it’s fine. Hence the theoretical (but hitherto unobserved tachyons).

If you look at the equation of the Lorentz Contraction, without reading anything else, you’ll see why you can’t go AT the speed of light—for the simple reason that you’ll be dividing by zero. The equation 1/sqrt(1-v^2/c^2), where v=c, you’d have 1–1=0, and that’s not allowed in our universe.

Pretty_Lilly's avatar

@neverawake & @ChazMaz
Actually that’s what his wife said “BUT” it was euphemism for something else !! XPP

Bugabear's avatar

Because for something to go faster than the speed of light it would have to have infinite energy. And that can’t happen because we are in a finite universe. I dont know what these people with the antimatter are talking about.They’re just regular matter with an opposite charge. And when it comes into contact with normal matter it teh asplode. Thats right. Dan brown was right about something.

Rarebear's avatar

@Bugabear Not exactly, see my post above. To be exact, you can’t accelerate faster than the speed of light from slower than the speed of light. If you start off faster than the speed of light you’re cool.

Bugabear's avatar

Yeah exactly. So…

Zaku's avatar

Unless there is a way to move something without applying force to accelerate it conventionally.

Apparently there are ways to send information faster than C.

mrentropy's avatar

@Rarebear The Universe would crash on a “Divide by Zero” error?

Rarebear's avatar

@mrentropy Well, it’s just that it’s not allowed. If you plug the Lorentz Contraction into an object accelerating towards the speed of light, you’ll end up with an option that has infinite mass, and is infinitely small in the direction of motion, and where time stops. It just doesn’t work.

cockswain's avatar

So if there is anything faster than the speed of light, it has been at that speed since the beginning of the universe. Should anything act on it to slow it down, it could never regain its original speed.

This is a cool conversation. The more massive something is, the more energy it has. The faster something moves, the more massive it becomes. The more massive something is, the lower the top speed it could possibly attain. Am I correct?

Thinking this way helps me understand Einstein’s quote slightly better: “It followed from the special theory of relativity that mass and energy are both but different manifestations of the same thing—a somewhat unfamiliar conception for the average mind.”

Rarebear's avatar

@cockswain In response to your first paragraph, not necessarily. It’s just that it can’t decelerate to the speed of light because of the divide by zero thing. It can move at any speed it wants to, as long as it’s still faster than light. But this is just hypothetical, as nothing like this has been observed.

In answer to the second paragraph, no. You’re confusing rest mass with relativistic mass. Rest mass is constant, no matter the velocity. As you gain velocity you gain relativistic mass. As you get to the speed of light, your relativistic mass is infinite, so it really doesn’t matter what your rest mass is. There’s no “top speed”. You need infinite energy and infiinite mass to get to the speed of light, so it doesn’t matter.

In response to your third paragraph, sort of. Einstein doesn’t say that energy and mass are the same thing, but that they’re interconvertable.

Bugabear's avatar

@Rarebear My point is if something is going at the speed of light it it’s all cool and what not. But in order to make it go faster you would need to add energy to it that just doesnt exist in this universe. Mathematically you could totally do that but in this particular universe you can’t.

Rarebear's avatar

Actually, no. It’s moving AT (don’t know how to bold) the speed of light that’s the problem. The only thing that can move at the speed of light are objects that have zero rest mass—i.e. photons. So you can’t accelerate to the speed of light. And I do agree that a different universe may have different laws.

dpworkin's avatar

@Rarebear right below the edit box is the key to text markup. emphasis (bolding) is text between underscores.

dpworkin's avatar

I learned that from Neils Bohr

Bugabear's avatar

yeah… So what are you saying? You seem to be saying the same thing over and over again. And then attempting to confuse me with math.

cockswain's avatar

@Rarebear Thanks for your input. I’m having trouble understanding relativistic vs rest mass. Let’s take a ball that weighs a pound. Will it weigh a pound at all speeds, or does it get heavier as it approaches C? Also, are you saying that given this same ball, it has a distinct feature called relativistic mass that does fluctuate with speed?

Bugabear's avatar

@cockswain As it approaches the speed of light it will begin start to weigh more. It’s “mass” wont get any heavier but it’s weight will increase. Unless you’re talking about Mass in special relativity.

cockswain's avatar

@Bugabear I don’t know what the hell I’m talking about

Rarebear's avatar

@Bugabear is right. The rest mass is the same. The relativistic mass increases. It’s why in the Large Hadron Collider they accelerate protons to incredible velocities, just under the speed of light. The relativistic masses increase so you get more bits when they collide.

cockswain's avatar

My understanding of weight is it’s a function of the strength of a gravitational field. How will the weight change? If a mass is moving in a outer space, would its weight increase still? Sorry, just don’t get it yet.

Also, when the particles move fast in the LHC and cause more bits when they collide, that just sounds like inertia. If you don’t mind, can you give a better explanation please?

dpworkin's avatar

Yeah, I meant above when I said that the LHC proves it every day, that if people want to understand this better they could read, in layman’s terms, how and why the LHC works.

cockswain's avatar

@dpworkin I have, but it’s been a while. Maybe I should again since it must not have stuck. I followed it closely at first, then it broke down right away and for a long time.

dpworkin's avatar

Well it’s running now!

cockswain's avatar

I know! I looked it up after your first comment. Apparently it has set a new energy record

dpworkin's avatar

From now on it will always be a record, whenever they up the EVs

Rarebear's avatar

@cockswain Yes. I will give you a better explanation and will clear it up for you. Right now, though, I’m in a hotel room in Chicago, trying to tally up a NCAA basketball pool I’m running (my bracket is, of course, busted). When I get back home tomorrow I’ll put some time into answering your question.

dpworkin's avatar

B-Ball over Higgs Bosons any day.

cockswain's avatar

I heard on NPR that there are usually about 2 perfect brackets in the nation every year. After losing a couple hundred bucks in the last 10 years, I’m done with it all.

Rarebear's avatar

@cockswain My pool is only 2 bucks a pop, so people don’t feel like they’re out anything. It’s just for fun, and I don’t take any cut so I don’t make any money off of it. Unless I win, of course, which I’ve never done.

dpworkin's avatar

Obama had a hell of a bracket last year.

dpworkin's avatar

we’re gonna get busted for being off topic

Rarebear's avatar

lol Let’s see how long it takes

mattbrowne's avatar

We know there is in fact something faster than the speed of light: the expansion of spacetime in our expanding universe. It’ll make our night sky darker and darker over time.

Rarebear's avatar

@mattbrowne Is correct. The actual expansion of the universe is happening much faster than the speed of light. I had avoided mentioning that because @cockswain was having some trouble with some of the concepts of Relativity and I didn’t want to muddy the issue.

CMaz's avatar

I understand how it is not possible to go faster then the speed of light. But then again I don’t.

Lets say we are in a spacecraft. Outside the gravitational pull of our solar system. I understand there is always a gravitational pull of some sort.

I stand on the nose of the spacecraft and either push off, or fire my rocket pack. Or the spacecraft has multiple stages. Now I am accelerating away.
Moving at a greater speed then the spacecraft. When dose this repetitive process cause an opposing effect?

You would think if you continuously repeat this process, you would eventually exceed the speed of light.

dpworkin's avatar

@ChazMaz Shit happens on your way there. if you had been paying attention, you might have noticed. Go look over this thread again and see what happens as you begin to approach the speed of light.

Rarebear's avatar

@ChazMaz You would think, but you don’t. If you had a clock on your ship, and an observer was watching your clock, as you got closer to the speed of light, the clock would slow down. Also, you’ll shrink in your direction of motion, and your mass will increase. If you got to the speed of light, you would shrink down to nothing, your clock would stop, and you’d have infinite mass as far as the observer is concerned.

@cockswain In regards to your question about gravitational fields and weight. Mass and weight are two different things. Your mass is constant, but your weight will change depending upon where you are. For example on Earth you may weigh 70 kg. On the moon, you’ll weigh 1/6 that. On Jupiter, you’d weigh a bunch more. But your mass is constant.

In regards to the LHC question and inertia, the short answer is yes. But the velocities are so high that the protons relativistic mass gives it more inertia than it would be just taking into account its velocity alone.

Rarebear's avatar

@dpworkin Be nice to Chaz. He asked a good question.

CMaz's avatar

@dpworkin – So it is that energy mass thing. Those changes in acceleration as subtle as they might be are causing a change in mass?

And @dpworkin is cool.

Rarebear's avatar

@ChazMaz I’m not sure I understand your question. Can you rephrase it?

dpworkin's avatar

he was lazy

CMaz's avatar

@dpworkin I was being honest. You asking that question might be lazy. But you are still the man. ;-)

As I push away from the spacecraft. Increasing my speed, moving closer and closer to the speed of light. My mass is changing?

Rarebear's avatar

@ChazMaz Your rest mass stays the same—you will perceive that you will be the same mass. An observer watching you, however, will see your mass increasing.
You might check out Episode 9 and Episode 44 of Astronomy Cast
http://www.astronomycast.com/category/physics/relativity/

CMaz's avatar

“An observer watching you”
See that is where I get thrown off. It almost seems what you are saying is I can move faster then the speed of light.
But others will not and can not see it that way.
I get the math, if it was not for that. It would seem like we were missing something.

TY for the link. I am going to check it out.

Rarebear's avatar

@ChazMaz “I get the math”. I remember once I was in a college physics course and I went to my physics professor to ask him about something. He showed me the math. I said pretty much exactly the same thing that you did. I said, “I get the math, I just don’t GET it.” He looked at me, and said, “You’re not an engineering major.” I said, “No.” He said, “You’re a science major.” I said, “Yes, why?” And he went on to tell me that engineers just care about the answer. Scientists want to know WHY—which is what you are asking. I’m impressed.

The short answer, that you’re not going to like, is “It doesn’t work that way.” But I’m going to have to go back to my books and read about it again so I can give you a cogent answer.

CMaz's avatar

”“It doesn’t work that way.”

Now that makes total sense to me. Really. :-)

dpworkin's avatar

I must be quite an oddity. I think I get it, and I can’t perform arithmetic.

Rarebear's avatar

@dpworkin It took me a very long time, and I had to read three books, until I finally “got” it. I can explain it, but not well. What I want to do is go back to The Elegant Universe (which has the best explanation of all my books), read it again, and then try to explain it.

dpworkin's avatar

What helped me enter the world of physics more than anything else was reading everything Feynman wrote, and then watching all the lectures. I just plug my ears and go la-la-la-la-la when he gets to the equations.

cockswain's avatar

@Rarebear Your explanation of weight is the same as my understanding. Above, @Bugabear said ”As it approaches the speed of light it will begin start to weigh more. It’s “mass” wont get any heavier but it’s weight will increase.” Then you said he was right, so I became very confused contemplating that one. I’m assuming this was just a mistake, and weight doesn’t play a role in the relativistic vs rest mass issue?

I’ll wait for your explanation from The Elegant Universe before I ask anything else.

Zaku's avatar

Just to add confusion, I feel I should add that from your own perspective, you’re not moving much at all. So if you can build a build a spaceship that will get you going say ten times light speed, you will not have any “speed limit” problems and will be able to get places at whatever speed you can engineer, from your own perspective. The side effect, supposedly, is that if you return someplace you’ve been before, you may notice that much more time seems to have passed there than you have seemed to have time pass where you were.

E.g. You zoom from Earth to Proxima Centauri and back in a year, then come home and find that every one on Earth has experienced many more years than you have in the meantime.

cockswain's avatar

@Zaku That part does not confuse me, but thanks for trying :)

Rarebear's avatar

@cockswain Okay, I’m just going to type the last couple of paragraphs. He explains it a lot better. This is from Brian Greene, The Elegant Universe page 52 hardcover version.

…Einstein’s equation gives us the most concrete explanationfor the central fact that nothing can travel faster than light speed. You may have wondered, for instance, why we can’t take some object, a muon say, that an accelerator has boosted up to 667 million mph, 99.5% of light speed—and “push it a bit harder,” getting it to 99.9 % of light speed, and “really push it harder” impelling it to cross the light-speed barrier. Einstein’s formula explains why such efforts will never succeed. The faster something moves, the more energy it has, and from Einstein’s formula we see that the more energy something has the more massive it becomes. Muons traveling at 99.9% of light speed, for example, weight a lot more than their stationary cousins. In fact, they are about 22 times as heavy, literally. ... But the more massive an object is, the harder it is to increase its speed. PUshing a child on a bicycle is one thing, pushing a Mack truck is quite another. So, as a muon moves more quickly it gets ever more difficult to further increase its speed. At 99.999% of light speed the mass of a muon has increased by a factor of 224; at 99.99999999% of light speed it has increased by a factor of more than 70,000. Since the mass of the muon increases without limit as its speed approaches that of light, it would require a push with an infinite amount of energy to reach or to cross the light barrier. This, of course, is impossible and absolutely nothing can travel faster than the speed of light.

cockswain's avatar

I guess one could liken it to how the graphs of some equations infinitely approach an asymptote. So if this has been experimentally proven that lightspeed is in fact a real and limiting factor, then this is just the way the universe is. And my question is answered. In summary, I was originally wondering if , regardless of how the equation works out, the equation was correct and C should in fact be light speed. In other words, is there any room for doubt about how much value we’ve given light speed? But thanks everyone for a wonderful discussion.

Rarebear's avatar

@cockswain Exactly. You’ve got it.
The speed of light has been experimentally determined, so there is a small bit of experimental error.

cockswain's avatar

Hmmmm. I wonder how Einstein figured that out? Must’ve been smart.

dpworkin's avatar

Thank the Lord we are being protected by beings from the future. How do I get one to give me some stock tips, though?

CyanoticWasp's avatar

@cockswain unless you show the dateline of the story (from 4 days ago), you know that people are going to believe and worry about this, don’t you? Some probably will anyway.

cockswain's avatar

What’s the point. He’ll just travel to a different date.

Did you notice he disappeared from his cell? Probably to go protect John Connor.

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