I do not post often; however, I asked this question in another thread and thought it might be worthy of its own.

If a person is traveling at light speed would they be able to see what is in front of their craft. Vision, from my understanding, is based on light reflected off of objects.

I suppose if you were travelling at the speed of light you would still see the stars in front of you but from the side windows you would see long streaks of light possibly.

Even more interesting (I think), and even though a comic first posed the question, it's relevant to think about:

You're traveling at the speed of light in a spacecraft (the comic used a car), and you trigger a flashlight (or similar front/direction of travel facing light) to shine.

(1) Does the light shine at all?
(2) If the light shines, does the beam (and thus the photons) extend outwards from the source?
(3) If therefore#1 is true, #2 would likely be true. That being the case, I've just enabled FTL travel (of photons albeit), and no less!

Put it another way, if I travel 100kph in a vehicle and fire a gun facing in the direction of travel, the projectile will be traveling at it's normal speed (minus a friction reduction) PLUS the speed of the moving vehicle.

Although in space there is little matter, it would reason to think we'd have a near-perfect vacuum, and thus, those photons would be going e2 (372,000 miles per second). At this speed, a light eminating from my spacecraft would travel R+e (r being relative speed, which is the speed of my spacecraft).

I've just proven (if #1 and #2 are in fact true) that FTL travel is possible, no?

The only problem with your argument is that the speed of light is a constant. It can always be relied upon to travel at 299,792,458 m / s. It is the constant in the same way gravity is a constant (Two objects, one heavier than the other, will fall at the same rate- 9.8 m/s), only more so. Say you had a radar that could measure the speed of a beam of light. If you were travelling in the car going 100 km/h, then the speed of light would still be 299792458 m/s. That is the nature of light. Were I to have a PhD in light particle physics, I would explain more. As for now, I can only tell you that the fastest ANYTHING can go in this observable universe is = to the speed of light.
As for the headlights, I believe the photons would pile up at the lightsource. They would move forward, but only because of photons piling on top of eachother. Think of pingpong balls filling a cylinder from the bottom up. Someone want to tell me the right answer? I'd love to know

Just a quick note the speed of c only applies to photons travelling in a Vacuum. Light does travel slower in other mediums.

Forgot about that trivial nugget of info It still stands that the speed of light is the end all be-all speed in our observable universe

Originally posted by TheGoodDoctorFunk
Forgot about that trivial nugget of info It still stands that the speed of light is the end all be-all speed in our observable universe

It may be. When Solar Flares happen why do Neutrons arrive at the detectors before the photons?

Also the Group Velocity can and has been accelorated up to 400 times the regular speed of c. Unfortunately no information can be disseminated this way but it does show that it is possible to exceed c in certain conditions.

Im not a scientist at all, but i saw a doco on the discovery science channel that kind of explains you question.
It said if we travels close to the speed of light that the world/universe would turn into like a matrix bullet mode, while after you break the threshold of the speed of light. If you are going faster than light, you would see the world or universe go in reverse/backwards.
Dont know how true this is, but it was sure intresting.

Wow, this is making my brain hurt....

Good question.

This exact question was raised on different thread months ago. The whole thread was dedicated to it. And, my thought has not changed over time.

You are in a car traveling at the speed of light. What would happen if you turn on your headlights? Most people say nothing, you are at the speed of light.

I answered that the light beams from the headlamps would continue to go out before you. Why? The car is at relative speed of ZERO. As far as the lamps are concerned, they are stationary.

Example: You are in a car going about 90 mph. You open the window and throw a speed ball forward of you, which, coupled with the car speed, goes, ohh... let's say 120 mph. Can anyone throw a ball that fast? No. But you, who were at a relative speed of ZERO, just threw a ball going 30 mph.

Make sense?

Car at light speed... lights going 2x speed of light, because the lamps are at zero.

I agree that the craft, or the car example you used, would be a zero point; and that, a beam of light would travel out from such craft at the speed of light plus the speed of the craft. Of couse, this is assuming that the speed of light is not a constant maximum speed--as some theories suggest.

My question is, would one be able to see debris, planets, etc. in front of the craft? It would stand to reason that one would only see distant objects and not objects directly in the path of the craft, since vision depends on reflected light.

[edit on 1-2-2006 by mo_trot]

Soothsayer, unfortunately that is - while logically sound - physically untrue.

Experiments have been performed to test for a substance called the "ether". Before Einstein it was theorized that this substance permeated nature, and was the medium through which light, as a wave, traversed.

So some scientists came up with a device to prove the ether's existance. However, what they found was just the opposite. The idea was that, if light travelled through the ether, then light travelling in the direction of the "flow" of the ether would cause the light to speed up - while in the other direction it would slow down. They tested the speed of light numerous times, at different parts in the earth's orbit (since Earth travels an elliptical orbit, at some parts it is moving away from the sun, and at other parts it is moving towards it). They found that no matter when or from what direction, the speed of light was always constant.

So, running forward at 2m/s with a flashlight does NOT make the light from the flashlight move forward at 2m/s plus the speed of light. It only moves at the speed of light regardless.

So, basically, the headlights release light, but the light will not go faster than the speed of light, and will "pile up" so to speak in front of the vehicle that is travelling at or near the speed of light.

Now the interesting question is, upon achieving a state FASTER than light (if we assume it to be possible, which - frankly - I do not believe to be so), do we create a "photonic boom"? Like a sonic boom, but instead with light.


Another thought just occured to me. How do electrons in orbit around nucluei react to speeds approaching light? Is their probability cloud changed to favour back-ended locations? Or does it not matter? Essentially - will the electron go faster than light to achieve a point on the opposite side of the atom?

Originally posted by mo_trot
If a person is traveling at light speed

No, it cannot happen.

Originally posted by Frosty

Originally posted by mo_trot
If a person is traveling at light speed

No, it cannot happen.

Uhh I think he was only hypothesising within the context of a thought experiment to make sense of Light. Einsteins thought experiment imagined himself riding a beam of light. Physically impossible, it's just another way to look at the problem.

Originally posted by sardion2000

Originally posted by Frosty

Originally posted by mo_trot
If a person is traveling at light speed

No, it cannot happen.

Uhh I think he was only hypothesising within the context of a thought experiment to make sense of Light. Einsteins thought experiment imagined himself riding a beam of light. Physically impossible, it's just another way to look at the problem.

Yes, and that is how Einstein came to the conclusion that a person cannot travel at the speed of light.

Originally posted by Yarium
Soothsayer, unfortunately that is - while logically sound - physically untrue.

Right. I was thinking the exact same thing.

The speed of light is constant unless it has anything tugging away on it. Let us for example say, it does not. The car example, the lights would remain stationary, not extending in front of you, as your car is already at the maximum speed that light can go.

While I am no physics major, I don't think the projection of light even at the maintained light speed can surpass the limit.

I'm not a physics major either. Yet.

I can tell of you though, that you kind of need to be to understand properly.

If you are travelling at the speed of light, and shine a light forwards, from a flashlight or whatever, you will observe that light moving away from you at the full speed of light.

A person off to the side of you would not see the same thing as you, they would in fact just see a single beam of light move by, were it that they could 'see' beams of light.

The fact that c, the speed of light is constant, and that t, the amount of time or x, the distance of space, is not constant, allows for your length to contract and your time to dilate in such a way (while travelling at near-light velocities) that the second beam would move away from you noticeably, but only to you.

I don't have my equations sheet with me, but I believe it's Lm=Lsgamma, or, movingLength=stationaryLength*1/root(1-v^2) (where v is 0.xx of c, a decimal amount of speed in the unit c) And ts=tmgamma.

It's fairly complex, but it is by no means a new question, and .. is actually "the question" that relativity answers. The fact that so few people in this thread knew what was going on shows that the real concepts of relativity don't get expressed very well to the mainstream public knowledge. Relativity does not just mean "you can't go faster than light" - it means that light is absolute while time is not, and regardless of you, or what you're doing, light will always do the same thing.

And to sardion: The thing with the several times faster is actually a very clever trick. Imagine setting several people with synchronised watches each 2 lightseconds apart. Then, go to one, and tell them to shout "Hello!" at 12:00:01, and go to the next, tell them to shout "Hello!" at 12:00:02, and continue. From 12:00:00 to 12:00:30 or whenever, it would appear that a message has travelled at twice the speed of light. As you said, no information is actually carried, and causality is not broken, but it's less impressive than it seems. By spending a phenomenally larger amount of setup time, we are able to get a phenomenally faster transmission, but it's useless. So, oh well.

Still a fun <$1000 experiment, though. A few hours of your time, an oscillator, 2 pulse generators(with controls for accuracy) and 100m or so of coaxial cable is, last I heard, all you need.

It never ceases to make me feel a little sick when a thread about how there's a problem with relativity, time, or 'dimensions' that expresses either a fundamental question of life that cannot be answered yet, or a very long ago answered question as some brand new insight and then proceeds to attempt to call down/change the science at hand. This alleged problem in established science leaves the door ajar for anyone with a theory, and that's just not the way it works. But every week, 5-20 times, it happens. I'm surprised I'm still answering. And it's not the poster's fault, they weren't here before, and it's not the fault of the repliers, who aren't required to know better, the mods are doing the best they can, and the only real solutions take a ton of work and upkeep. It's a quandary, and I hate that it's there.

Sorry if I've come off wrong. It's too late at night to be explaining physics.

(Plus, I just worked out probability of outcomes of 3 attacker : 2 defender rolls in risk. It turns out that the defender is twice as likely to flat out win than the attacker, but it is far likelier that the outcome will be a draw, 6 times likelier to be a draw than a win for defender, and 14 times likelier for attacker. The actual numbers, going atk win:def win:tie are roughly (I may have made a mistake somewhere) 520:1183:6073. Enjoy that if you will. )

EDIT: I forgot to answer the very first question. Yes, you'll see things in front of you. The speed you're moving at in no way affects the way the matter that constitutes 'you' interacts with photons, so, you'll see everything pretty much normally. It will still move towards you at lightspeed, you'll still move wherever at whatever speed. What's behind you will also still send photons at you that, to you, move at light speed, and catch up to you accordingly.

[edit on 3-2-2006 by Viendin]

Doesn't that mean we could theoretically launch a ship, and then launch a ship from that ship, and launch a ship from that ship, etc, to attain incredible speeds?

I have done a bit of research on this since I origionally posted the question with very little success. Published documents are about as mixed as the responses to this thread. Some say that a light directed in front of the craft would result in piling neutrons as thegooddoctorfunk stated; others say that light speed is not constant and the beam would travel. Secondly, there are sites that state that one would not have any periphrial (sp?) vision from the craft. One would only see reflected light or light sources directly in front of the craft. These sources would be consolodated and all appear as white light.

I will research this further after the weekend and provide links to the more credible sites. Unless something changes, no real revolations will come from the research since most publications are only theory.

The problem with attempting to figure out what the actual physical area would like like while you actually travelled at light speed is that you can't.

Because matter doesn't travel at light speed, speculating upon the interactions of matter at light speed is irrelevant, and impossible to prove. We can talk about interactions at 99.99999% of the speed of light, in which case, you should be able to see everything because light will always be constant. I'm not wrong on that, it will be moving at light speed towards you, past you, away from you, from side to side of you, regardless of the speed at which you travel, and time and space will warp to make some of the ends meet.

This isn't like one of Einstein's thought experiments - his were of the sort of "If I were a beam of light, and I shot another, how fast would it go?" Not "What physical effects would lightspeed travel have on me?". It'd be nice to know, or to think about, but we can't reach a definitive answer of what would happen actually at light speed.

Edit: And, TheGoodDoctorFunk was very much right, up until the piling bit. The photons do move away from you, but they are still travelling at 299,792,458m/s to all observers.

[edit on 3-2-2006 by Viendin]