# How can you move at the speed of light?

1. Jul 7, 2003

### Draco

I mean, is it possible for Space Ships to travel at the speed of light?
Wouldn't it be impossible? I'm just curious about it all.

Last edited by a moderator: Jul 7, 2003
2. Jul 7, 2003

### HallsofIvy

No. Nothing having non-zero rest mass can move at, or faster than, the speed of light (with respect to any other non-zero rest mass body).

3. Jul 13, 2003

### jammieg

Not provable or disprovable at this time. What is mass? The interacttion of charges on charges to get a resulting comparable force? So is it that the faster things move the less interaction and the slower they move the more (relatively)?So virtually zero mass is no interaction or such a slight interaction as to be unobserved? Even light has mass or it would not be affected at all by gravity, it would not bend right.
Aren't all speeds relative to the obserever? Hypothetically speaking if something were moving faster than light I wonder what we would percieve it as if at all...Given that most of the particles in the universe are not in some degree of control over their own speeds, the bulk of matter in hypothesis that is moving faster than light is of no free will and so might occasionally pop into or out of our observable existence, but take a large mass of particles that are controlled by a person and can choose to deccelerate into this observable speed or light frame and the whole ship might seem to pop into existence instead of just one particle that by chance deccelerated to a speed that could be detected by some instrument or far less likely sight. It is possible that all our fancy instruments are constrained to one particular frame of reference and they can only detect what is interactable to them within this frame.
The catch may be that at the speed of light a normal hydrogen atom would become light to the observer or in any case not be able to return to the state of the hydrogen atom, or it may just be relative to the observer but that would suggest that the faster we move the more light takes on the properties of standard matter at some point and the slower the more matter takes on light properties... If this were true then very cold instruments should see more light than hot instruments, I don't think that is true, but if it is then it's a plausible case for above light speed travel, I mean if simply adjusting the temperature of one's telescope to near absolute zero allows one to see more light in the universe then that would be very strange and inexplicable. Stranger still what if light speed is not fixed but merely the relative speed difference of observer particle to target particle, that the observer particle itself is not fixed but merely relative to something else and so on? That this speed difference threshold is merely just a point at which matter to matter interaction takes on more distinct properties that we are more readily to notice with our eyes, but it is still relative from observer particle to target particle and a more obvious difference in relative speeds.

4. Jul 14, 2003

### Staff: Mentor

Lotta misconceptions in there. You should read up a little on Relativity. "A Brief History of Time" is a good starting point, but lots of websites will do a decent job.

A few points:
-light has no mass.
-gravity bends space, light travels in a straight line through curved space.
-reference frame doesn't matter. you will never see something travel faster than light.
-anything regardless of velocity is observable - you just have to collide with it.
-light always looks the same, regardless of your frame of reference.

Last edited: Jul 14, 2003
5. Jul 14, 2003

### jcsd

Yes c, the speed of light is pretty much the universal speed limit, though it is theoretically possible that particles may exist that already travel faster than the speed of light (tachyons), however these may not travel at or below the speed of light and have the interesting property of imaginery mass. Also quantum tunnelling will allow particles to have average speeds greater than the speed of light, even though they never actually travel that fast.

There really is no conceivable way of making a starship made out of normal matter travel at or above the speed of light though.

Light has zero rest mass (which is usually meant when talking about mass).

6. Jul 15, 2003

### Imagine

Bonjour,

I would invite you to look at water to visualize propagation speed limit and neiborhood effects.

When you drop a rock into calm water, from an airborn view, you see concentric waves propagating around the drop position. From the beach view, you see waves coming to you and with your friend, sitting on the beach near you, you will be able to locate the drop position using triangulation. Note also that these waves propagate at a certain speed limit, called here "V".

Now, suppose a sailboat, or a water ship, is navigating on the river at a speed superior to "V". From an airborn view, you see V-shaped waves propagating at "V" speed. From the beach view, you see "front-flat" waves coming to you. You are able to point the source, the direction. Your friend, sitting on the beach near you (not so near!), see "front-flat" waves coming to him and is able to point the source, the direction. But both direction will be parallel and wouldn't be able to locate the source. The source seams to come from infinite distance. (Except if your friend is on the other river's side and you are able to communicate enough "rapidly" to synchronize your clocks)

7. Jul 15, 2003

### Imagine

Rebonjour,

IMO, we may frequently find tachyons on this earth.

My friend is working for the government. He is scheduled to stop working at 17H00. He is at home at 16H30 (in the same timezone ) But something strange, he left home at 8H30 and start working at 8H00.

That's faster than light but not between 8H00 and 17H00.