Why you can't travel faster than the speed of light

[Syzygy2011]

Einsteins theory is something we all understand today. It's tomorrows theories and discoveries that we don't know/haven't discovered yet. We are still in the dark ages with what we know.... but time travel, exceeding the speed of light etc is possible... we just don't know how yet!

[Earl]

Einsteins theory is something we all understand today. It's tomorrows theories and discoveries that we don't know/haven't discovered yet. We are still in the dark ages with what we know.... but time travel, exceeding the speed of light etc is possible... we just don't know how yet!

Well no it could well not be, what we might need to do is find out how to manipulate Space not speed. Star Trek Warp Space, Dune Fold Space. Travelling without moving.

Of course Sci-Fi but who knows it will only take a Genius to open up more possibility's and we should never limit what is possible.

But as for physically getting a mass to the speed of light, that is probably not the way to do it.

[Jack123456]

If light (photons) have no mass, how could they be affected by gravity and get pulled into a black hole? Isn't gravity defined as to objects with mass interacting with each other?

also, if light is "sucked" into a black hole, doesn't it travel faster than the speed of light when being sucked in?

[Earl]

If light (photons) have no mass, how could they be affected by gravity and get pulled into a black hole? Isn't gravity defined as to objects with mass interacting with each other?

also, if light is "sucked" into a black hole, doesn't it travel faster than the speed of light when being sucked in?

Photons travel through space, the space is bent by gravity so the path of the photon bends with the space.

[Jack123456]

aaah, that makes sense. thanks

[Syzygy2011]

Photons travel through space, the space is bent by gravity so the path of the photon bends with the space.

Correct me if I'm wrong but didn't Einstein say that anything that is traveling at the 'Speed of light' must go in a straight line?

interesting point about 'Bending' light!

[scogyrd]

Photons travel through space, the space is bent by gravity so the path of the photon bends with the space.

If protons have no mass and gravity isn't affecting them then what force is causing them to follow the bent space? Why can't they just ignore it and carry on on their intended path?

I've probably got it all wrong but if you don't ask you'll never know.

[Macavity]

Is "Big Bang" now deprecated? And by whom? One might indeed

HOPE that FTL travel will eventually be possible, but...

I think science [particle physics] has been doing "pretty well" of late re. experiment confirming theory. Though "dramatic" results seem to have somewhat dried up? <G> Without certainty (one might FEEL that?) theory is providing the most likely explanation for many phenomena. Or at least the basis of something that can be refined, rather than completely overturned. The lack of complete explanations for everything does not favour (popular ideas of) "anything goes". But that's just a personal prejudice!

The problem for the lay public - And MANY working scientists, is to make a valid (objective) criticism of current theory? At least in the sense that only a FEW... geniuses, really understand "the maths" behind it? And, on that, I gave up, a long time ago...

[Earl]

Correct me if I'm wrong but didn't Einstein say that anything that is traveling at the 'Speed of light' must go in a straight line?

interesting point about 'Bending' light!

It still is, it is the space that is bent, this makes it appear from an observers view point that the light is bent however it is the space that is bent.

[Earl]

If protons have no mass and gravity isn't affecting them then what force is causing them to follow the bent space? Why can't they just ignore it and carry on on their intended path?

I've probably got it all wrong but if you don't ask you'll never know.

They go through space in a straight line if space bends they still go in the straight line according to the bend.

yeah it sounds a tad odd, i scratched my head with it, its a "it is but it isnt" thing.

[Si W]

Using warp theory you could.

[nightvision]

I see one statement in the original post that I am not comfortable with: " ...since there is no gravity in space".

I would say there is gravity everywhere or we wouldn't have an interactive universe. The only reason people in the ISS experience weightlessness is because they are falling/orbiting at a specific speed.

For me this raises a thought (and probably highlights my limited understanding ):

It's gravity and not mass that limits how much energy/speed you can impart/gain, the accelerating object creates more gravity as it acquires more mass, mass and gravity which interacts with the gravitational locality. The implication is that for a given amount of energy how close you get to the speed of light is dependent upon the local gravitational environment. I believe this thought model could help explain the unexpectedly high peripheral rotational rates seen in some spiral galaxies.

[Jack123456]

Could someone tell me if this makes any sense?

as you increase towards the speed of light, time slows down. so if youaccelerated towards the speed of light, the speed of light itself would increase, because the speed of light is dependand on time.

for example, if the speed of light was 10m/s (i know it isn't, but i'm just making numbers up to help explain it easier), and at the speed of light, time slowed down by half (1second would take 2 seconds to pass). The spped of light would then be 20m/s because time has slowed.

Therefore, for something to travel at the speed of light, time would be stopped, and travel would be instantanious.

Also, this would suggest why you could never travel at the speed of light, because the close you got to it, the further away it would become.

[toml42]

If you travel at the speed of light, time stops!

Which raises some interesting philosophical discourse, since a photon does not exist in its own reference frame!

It measures no time at all between being created and destroyed, so in what sense can it be said to exist?

[JAllen]

The way I think of the speed of light is by using Maxwell's equations for electromagnetism. You can use these to derive an equation which has the same form as one that explains how waves travel. Electromagnetic wave equation - Wikipedia, the free encyclopedia

The difference is that the electromagnetic version has a factor of the permittivity of free space multiplied by the permeability compared to one over the speed squared for the generic equation. This implies that the speed of an electromagnetic wave (light) is one over the squareroot of the permittivity multiplied by the permeability.

These are both just constants and do not change if you change your speed and the Relativity Principle states that the laws of physics are the same regardless of your speed, therefore the speed of light has to be a constant and the same for all observers.

Now, because people can travel at different speeds but still see light travelling at the same speed, this means that something else has to vary, which is where the more exotic effects such as time dilation and length contraction come in.

As has already been said, the faster you travel the higher your effective mass. This means that more and more energy is needed to keep increasing your speed and that an infinite amount is actually required to reach the speed of light. This is why massive objects cannot travel at the speed of light, or faster.

I apologise for the maths, but I feel it is necessary to explain things fully. Hopefully I've written it in a way that's easy enough to understand.

[rabbithutch]

Again, demonstrating my ignorance and inability to be embarrassed by it, I must question the statement that photons have no mass. I'm making a bit of a leap here by accepting that c=the speed of light and light=photons, but taking that as given, and, if the m, or mass, in the equation doesn't exist because photons have no mass, then . . .

E = (nothing)©^2 + (pc)^2

I substituted 'nothing' lest 'zero' be an inappropriate quantity in this context; so it makes no sense to me at all. Adding momentum (p) gives no further understanding, in my view. 'Nothing' times the speed of light squared is nothing still and adding the speed of light squared times the momentum of photons puzzles me further because I thought that momentum was, by definition, the product of mass times velocity. If there is no mass, can there be momentum?

So, to my inadequate training and intellect, the equation resolves to Energy being equal to the speed of light squared.

I've ordered both the Bordanis and Anderson books. Whilst searching for used copies I came across a title by Bill Bryson, A Short History of Nearly Everything. Could anyone advise me on whether Bryson, too, might help me grasp more of this (or be at all interesting)?

Age prevents me ever putting any new-found knowledge to any use, but perhaps exercising the brain will hold old-timers disease at bay for a bit.

The knowledge, understanding, intelligence, patience and generosity here are marvelous. Thank you, All!

[JAllen]

You are right about the first part being nothing, as this depends on an objects rest mass, which is zero for a photon. As light has energy, this means it therefore has momentum as E=pc.

This is a very hard concept to grasp, given that the classical momentum is indeed mass times velocity. Classical physics is only approximately right however, with more accurate predictions given by quantum mechanics or relativity, depending on the situation.

It has been shown experimentally that light does have momentum, for example it is necessary for light to have momentum for laser (Doppler) cooling to work.

[toml42]

There is no shame in admitting ignorance whilst seeking knowledge!

You may have missed it at the end of one of my earlier posts, but momentum isn't really mass x velocity, this is just a convenient approximation for massive objects moving at everyday speeds.

please fasten your seatbelts, as the only way to explain why requires a little maths:

this is the real equation for momentum. in every day scenarios, where v is much, much smaller than c, the bottom of the fraction disappears, and we are left with the familiar p = mv

however, if we're talking about light, traveling at c, with m=0, this equation no longer makes sense. you have 1-1 = 0 on the bottom, and 0 on the top.

what is 0 divided by 0? it is undefined, there is no single correct result - this equation has broken down.

this is why we use the alternative formulation for momentum when talking about light, because it does give meaningful answers:

p = h / wavelength

this is known as the de broglie formula, and bear in mind that it applies to everything - everything in the universe can be considered a wave with a characteristic wavelength!

[rabbithutch]

Thanks, Jamie and Tom!

So, I need to work on my understanding of momentum, too, I see.

That does shed light (sorry, awful pun ) on the subject, though.