Why Cant We Go Faster Than Light?

[GrandMasterK]

Im wondering what the reason is. Is it a rule because we cant push objects that fast with any technology we can come up with or is the rule there because of some univerisal law meaning that there's no such thing in the universe that would allow us to do that?

 

What happens to you at light speed, what if I were to be able to a bullet and shoot it out into space faster then light like 200,000 miles a second, would it seize to exsist, would it create a black hole would it just become invisible and move really really fast, what would happen?

[danny8522003]

Im guessing infinite mass = infinite gravity. Therefore it would probably 'eat' the universe.

[GrandMasterK]

mass=gravity?

 

Does this mean that in a very small supply I have gravity around my body????

 

Can you be more specific with the eatting the unvierse thing.

[danny8522003]

Yes it does.

 

By eat, i mean everything in the universe would be attracted towards it and would be crushed into a singularity.

 

I just found something which is quite interesting:

http://news.bbc.co.uk/1/hi/sci/tech/781199.stm

[Inferno]

From what I understand, its a physical barrier. As you get closer to light-speed, your mass becomes less and your density becomes greater. Basically, you get really small and really heavy. At the barrier of light-speed, you are supposed to have no mass and infinite density. Theres one problem with that- how to accelerate someting infinitely heavy. The object being accelerated would get heavier and heavier, but it would need to be accelerated faster and faster. Thus, an infinite amount of energy would be needed to push something to light-speed. Impossible.

[danny8522003]

Your mass becomes less?

 

I thought your mass increased as you got closer to c. This is because you need HUGE amounts of energy and energy has mass (E=mc^2). Therefore, as you increase the energy input, the mass of the object increases and becomes more resistant to acceleration. Thus requiring more and more energy, making travelling at c with mass, impossible.

[J'Dona]

As an object's velocity increases, its mass increases (look here for a page with the formula). It increases in such a way that if its speed were to reach the speed of light, it would basically have infinite mass, and any effort to accelerate an object to that speed would require infinite energy (since you would need a greater and greater force to bring an object closer and closer to the speed of light as its mass increased). So it's a physical limitation, not a technical one; all theorised faster-than-light propulsion technologies in science fiction and that have to use elaborate things like wormholes to try and get past this issue.

 

Things don't become smaller as they approach light speed, but they may appear to to an outside observer. I think this is called Lorentz contraction, and occurs when, say, a stationary observer watches an object passing by at close to the speed of light (or the observer can be moving and the object can be stationary, same result. Each appears contracted to the other).

[Kyrisch]

Is that why the stars smear whenever ships go into hyperspace or whatever in the sci-fi movies?

[Inferno]

As an object's velocity increases' date=' its mass increases (look here for a page with the formula). It increases in such a way that if its speed were to reach the speed of light, it would basically have infinite mass, and any effort to accelerate an object to that speed would require infinite energy (since you would need a greater and greater force to bring an object closer and closer to the speed of light as its mass increased). So it's a physical limitation, not a technical one; all theorised faster-than-light propulsion technologies in science fiction and that have to use elaborate things like wormholes to try and get past this issue.

 

Things don't become smaller as they approach light speed, but they may appear to to an outside observer. I think this is called Lorentz contraction, and occurs when, say, a stationary observer watches an object passing by at close to the speed of light (or the observer can be moving and the object can be stationary, same result. Each appears contracted to the other).

 

I stand corrected. I believe I am correct about the infinite amount of energy being needed to push something to the speed of light, though. Someone tell me if Im wrong.

[danny8522003]

I stand corrected. I believe I am correct about the infinite amount of energy being needed to push something to the speed of light, though. Someone tell me if Im wrong.

Yes you are correct.

[timo]

One reason why no information should propagate faster than light is causality. Two events are considered causally connected if there is a non-spacelike (no faster than light contributiuons) connection curve between them.

The interesting feature about those causally connected events is that they will have the same time ordering in any coordinate system (except under time-reversal, of course). Therefore, distinguishing "cause" and "effect" makes sense as the cause will always come before the effect. When nothing can propagate faster than light, all efects will have causally connected causes.

If you allow for ftl propagation, you can have effects with non-causally connected causes. In this case you can find a coordinate system in which the effect happens before the cause which is weird, at least. Distinguishing cause and effect is not an invariant (under coordinate transformations) statement anymore. And invariant statements are kind of a holy cow in a physics which states that all coordinate systems are equaly correct.

[Daecon]

That's an interesting point... mass becoming infinite. Even if *theoretically* you have two objects, (A) has a mass of say "10" and (B) has a mass of "10,000" both would obtain infinite mass at light speed, and therefore become equal?

 

Could it be possible that if matter were to travel at light speed, because of relative contraction, it would actually become 2-dimensional? And because that dosn't really work in a 3-dimensional Universe, it's impossible for matter to achieve light speed, rather than due to reasons of mass.

 

Of course it could always require infinite energy to be able to push something into 2-dimensions. Perhaps, in a crazy world, energy isn't expended on acceleration, but on dimensional contraction - and "acceleration" is simply a side effect we see, and have associated with it instead.

 

"Infinity" is your way of knowing when to debug the Universe.

[GrandMasterK]

Light is a wave right? Are there any kinds of waves that are human created?

 

Im guessing waves dont have any mass on account of the whole infinite mass thing inwhich case light speed wouldnt be light speed, sooo will we ever be able to do something like turn a particle into a wave and blast it away somehow.

 

Im not even sure what the heck a wave is as far as it's psyhical presence in the universe. The Force behind magnets is a wave right?

 

What if you could make a giant magnet the size of Jupiter and place another one say 2 million miles away and they were both opposites. And im talkin about as much magnetic force as you can fit into an object that size. I know they'd go faster then the speed of light despite how big they are because like you said, infinite mass. But could you mimic the force of a blackhole using magnetic waves or artificial gravity and pull a wave in faster then the speed of light.

 

If you could do something wild like have a spaceship that creates and destroys blackholes say...exactly a mile away or however much space you need and did it so fast you dont even know it's happening, like a million times a second or whatever makes sense mathematically. So it's created, pulls you, gets destroyed before you run into it, another one gets created and so on and so fourth.

 

So lets say, your in a space ship and you flick a switch and it starts the black hole process while simultaneously turning the ship into nothing but a wave so the black holes pull you along. Wait a minute, no one ever said black holes pull light in faster then the speed of light, just that light cant escape.....

 

Can anybody work off that idea and make it make sense. Ignoring the fact that we wouldnt be able to make it.

 

I've never heard anybody say anything about light being pushed to go faster so I figure it's not possible but i'll ask anyway, has anybody pushed light faster? If you could, even by 1MPH, would anything crazy happen?

[GrandMasterK]

I'd really like that "what is a wave" question answered because I dont understand things like:

 

how does light travel?

 

Are all waves (Electromagnetic etc) light waves, because I know they travel at the light speed, but once again I have no idea what makes them travel?

[timo]

Are all waves (Electromagnetic etc) light waves ...

The physical description of a plain wave is f(x, t) = C exp(i(kx - wt)) with three -intially- arbitrary parameters C, k, w. Plain waves for massive particles exists and have a different relation between w and k than plain waves for massless -lightlike- waves (this relation is called "dispersion relation"; the name stems from optics, I think). In classical QM, particles are described by waves, which can be constructed by adding up plain waves : [math] \psi(x,t) = \sum_i C_i \exp [ i (k_i x - w_i t) ] [/math] (the sum goes to an integral, but that´s not my point here).

 

..., because I know they travel at the light speed, but once again I have no idea what makes them travel?

The square of the wave´s amplitude is considered the probability density for the postion. So if you find an area A in which the sum over the squared amplitudes almost equals the total sum over the squared amplitudes, you say that the particle is in this area. In contrast to plain waves, where the amplitude squared is always |C|² for all times t and all positions x, the sum of those plain waves can produce almost arbitrary distributions. The area A which gives most contribution to the sum of the squared amplitudes can change with time. This is considered as "the particle moves". The area does not nessecarlily have to move at lightspeed.

Might be an interesting weekend project to write few programs visualizing this aspect of QM. So if anyone knows of a suitable computer language for doing so, pls PM me. Python is not suitable as it seems too big to download, ISO C++ doesn´t seem good as I want to make a visualization w/o bothering about details like plotting the data or platform dependence (OpenGl is not an option), Mathematica isn´t free, dunno about Java. Inbuilt FFT, C-numbers and OOP structure would be greatly appreciated but are not really nessecary.

 

And finally: Your question is rather unrelated to Relativity. So if you have further questions on this topic, do a search in the "Quantum Mechanics" section or open a new thread there if you don´t find answers to your questions.

[Severian]

I want to comment on the old bugbear again: it is bad form to define mass in a non-covariant way. The mass of an object should not change with reference frame - the mass of an object is defined as what you would measure for its mass in its own rest frame. Let's call this 'm'.

 

Then momentum of the object is [math]p=\gamma m v[/math] where [math]\gamma = \frac{1}{\sqrt{1-v^2/c^2}}[/math] and v is the velocity. Certain text books/teachers have a habit of absorbing the [math]\gamma[/math] into the definition of mass (lets call this m'), so

 

[math]p = \gamma mv = m^{\prime} v[/math] where [math]m^{\prime}=\gamma m[/math]

 

While there is technically nothing wrong with this, it is rather bad form and at odds with all the conventions used by scientists. It is better to define properties of objects which do not change with reference frame.

 

So, mass does not change with reference frame, but the relation between velocity and momentum is non-linear.

[wormholeman]

I have an interesting thought.

 

What if there was a beam of light traveling in space, and at the end of the beam of light there was another source of a beam of light. Would the first beam of light which is traveling at 186.000 miles per second push the beam of light at the end of it to 372.000 miles per second? I wonder?

 

[Kyrisch]

No, because the second beam of light would be traveling at the same speed as the first beam of light. For instance, if two cars were bumper-to-bumper and both were driving at twenty miles per hour, the second car would be moving away from the first car at the same speed as the first car would be moving toward it, and so the second car would not be pushed at all by the first car.

[wormholeman]

I believe your car analogy is wrong. Because a beam of light behaves differently than a car. A car is the only thing that travels. A beam of light, like in my example, it has 3 parts traveling in sequence.

[CPL.Luke]

look at the equation gamma m c^2 and solve for the energy with a velocity of c and a mass of 1 (for simplicity)

 

you'll get infinity for an answer. This means that there is infinite energy required for one to travel faster than light, therefore it is impossible to accelerate to C because it would require you to place infinite energy on the object that is supposed to travel at C

[herme3]

How come everyone is saying that traveling at the speed of light will give you infinite mass? The speed of light is a number, so wouldn't your mass be a number? Wouldn't an infinite mass would require an infinite velocity?

[CPL.Luke]

they're using relativistic mass and under most circumstances you shouldn't use that. Instead use energy and you would get infinite energy from travelling at C, This is obvious from solving the full energy equation from special relativity, which is (lorentz factor)(mass)(C^2)

 

at C the lorentz factor goes to infinity

 

this doesn't apply to light, as light does not have mass, but does have enrgy which is = to (planks constant)(frequency of the light)

[herme3]

they're using relativistic mass and under most circumstances you shouldn't use that. Instead use energy and you would get infinite energy from travelling at C' date=' This is obvious from solving the full energy equation from special relativity, which is (lorentz factor)(mass)(C^2)

 

at C the lorentz factor goes to infinity

 

this doesn't apply to light, as light does not have mass, but does have enrgy which is = to (planks constant)(frequency of the light)[/quote']

 

Ok, I am really bad at math, so I can't solve formulas very well. However, to get the answer of infinity, wouldn't one of the numbers in the problem need to be infinity?

 

(number)+(number)=number

 

(infinity)+(number)=infinity

 

(infinity)+(infinity)=infinity

[CPL.Luke]

no, look at the formula

 

for instance 1/0 = infinity (simplified from math jargon)

 

jsut solve it and you will see, its all in algebra 1level math

[wormholeman]