Speed of Light question

Hold on

you forgot EJay has brakes at his disposal. He will slow down and return with a grin to see old YOU.

Sorry .....Just having some fun.

The universe ending for the passenger. I never thought about it that way, typically zero time to me has meant being every place in the universe at the same moment in time. It is rather a slippery slope though the same theory using to predict the results also says the speed of light is unattainable for any object with rest mass.

Then you can also consider quantum electrodynamics. A particle moving faster than light goes backwards in time, with a charge reversal, it's enough to give anybody a headache.

I guess the pertinent question is do end up at the beginning of the universe, or the end of the universe. Obviously you could end up any place in the universe, however having time stopped from your perspective would make it impossible for you to apply the brakes when you got there. One way or the other, I can see I'm going to have to limit my top speed to .99999999999999999999999999999999999C and that'll be a problem my brakes overheat slowing down from 140 MPH

Just what I love, an argument between 2 scientists about things that can't be proven. What a hoot!!!

Actually this is not a very accurate description of what you would observe at high speed. True, the outside universe seems to slow down if you compensate for your movement . But, if you head towards some far distant part of the universe, the simple fact that you are getting nearer to it will make events there seem to occur in a speeded up fashion. This is actually a much bigger effect than the special relativistic one due to the calculation of the Lorentz factor. Perhaps the simplest example is that light from a star you head towards will be blue shifted (higher frequency = "faster").

Interesting thought Elroch. I'll have a second thought on this... ... Thanks. (Keep in touch).

I had a moment of weakness when I submitted this. I just knew one of my many betters would show up and do me in. Thanks G.K.!

I like what you said about the observer not seeing light "coming out" of the headlights.

-A-

Hi -A-... I didn't mean to do you in... ...

In fact things are not so simple. For example, I thaught about the following: If you could travel (in a magical way) at a speed exactly c you should be "blind" about what there is in front of you. As everything around you moves at speed c (with respect to your reference frame) and passes you on, you are able to see in front of you only whatever is already behind you. Or, in other words, as you travel you can see only this part of the universe which you have already left behind. And you see your "target" only at the exact moment that you hit it. And you don't know what you are going to meet.

In post #63 Elroch has putted another interesting point. The "blue shift" of the light as you aproach a target (i.e. a planet) at speed very near c. I'll have a second thought on this.

May I start with the "smart-alec" answer? Yes. All trains are capable of travel at the speed of light.

The sober answer is, how are you measuring?

Yes. The locomotives that were designed to travel at the speed of light had. Lazar intensified headlights that have a light beam that travels at 103% of the standard speed of light

Dang.

Wonder how many lumens that thing put out, and if they make a pair to retro-fit to a '97 Caravan?

The light wave would only be projected off the sides, essentially be pushed from the velocity source and it's incoming vector, perpendicular to linear travel.

Think about this scenario. If you go down to the station early in the morning and a see a line of pufferbellies all in a row... No, that's the wrong one. OK, try this. You see a locomotive sitting there. You walk over, open your one-legged birding stool, look at your watch, and sit down. Later you look again at your watch and note that five minutes have passed. You see the locomotive is still there in the same place.

So, being the smart cookie your mom knew you could be, you conclude the locomotive has traveled forward in time. How fast? Why, at the speed of light, of course. With a sigh of bitter resignation at the futility of measuring speed when the rulers and clocks aren't constant, you shout to the engineer to turn on the headlight. He does so and you see the beam light up the Hooters billboard a half kilometer down the track.

Or, you might try something like this. Find a very straight, very long section of track. Stand in the middle. Have a train approach you at the speed of light. Agree with the engineer aforehand that at some point he will turn on the light and you will jump out of the way as soon as you measure the light. Well, actually, have your brother-in-law do this one - he needs the practice.

My point in this rambling discourse is that, in SR, you have to be very specific about what you're attempting to measure and how you are going to do it. Otherwise, the question has a multitude of answers, many of them peculiar.

"...a multitude of answers, many of them peculiar..."

"Many" of them?!? And which ones, pray tell, are the not-so-peculiar ones? I sure couldn't pick 'em out!

FWIW, my thought is that the light will be propagated forward at speed c from the point of emission regardless of whether that point is moving itself, or not. It's not the same as sound waves which are transmitted by the medium in which they move. Light can move in a vacuum (in space, no one can hear you fart, but they can see you grab your nose). So the light will preceed the train, but the train (must be that famous Hell-bound train of song and story) will be right behind it. Unlike a slower Amtrak train that will be far out-paced by the light.

Unless I have failed in the mission given me by my masters on the third moon of Xerswq, all my answers are nutty, not peculiar.

But, if you insist on the truth (why, I'll never know, lunacy being so more realistic), here's a neat little applet to play with. Choose experiment 6 and you can switch back and forth between the observer's frame and the car's frame.

http://www.its.caltech.edu/~phys1/java/phys1/Einstein/Einstein.html

OK, so it's a car not a train. This is from Caltech - they don't know the difference.

Classic relativity question. The answer, according to Einstein's theory is that the speed of light is relative to the observer. The observer of the trains headlight is on the train and so the light from the headlight moves away from this observer at - you guessed it - the speed of light.

This is a nonsensical way of looking at the real problems Einstein was trying to address. In real terms our galaxy appears to be heading away from the center of the universe at very nearly the speed of light and yet light emitted from our sun appears to us to travel in every direction at the speed of light.

From the point of view of an observer at the center of the universe the light from our sun heading in his or her direction is first red shifted into near oblivion and then gravitationally lensed back in our direction so from his or her perspective we don't exist. Equally, there is no way for us to directly observe the center of the universe. We are even having great difficulty determining a compass heading for such a critter.

Try thinking of it this way. The mathematics of infinity is fundamentally different than finite mathematics. In finite mathematics 1 plus 1 is 2. In infinite mathematics 1 infinity plus another infinity is still a single infinity. Since infinities don't add properly you can't multiply them either. Neither can you take the sine or calculate a tangent. If you want to mathematically describe an infinite universe sensibly you will have to learn Einstein's equations and learn how to use them, or come up with something better yourself.

Best wishes,

Mr. Gee

Yes......On the other hand if you were in an airplane going 3,000 mph and you shot the onboard gun that had bullets that had an initial speed exiting the barrel of 3,000 mph would the bullets leave the barrel? The answer is of course.

My question for you is where in the world did you find such a cool fast moving train and how much is mach one ride?

Mike

It was going the speed of light, I was banging on the door of a boarded up Starbucks and whoosh. I was boarded too. I need some Dramamine friend, the math is too hard.

I know the feeking. My exwife was from Rupert WV and in 5 years of being together there was a lot of whoosh factor.

Hello miketheboilerguy:

I think your analogy makes it a lot easier to understand the speed of light question as posed.

My first thought it seems is pretty much the same as yours. That all things being 'relative', in relative terms and comparison, the light from a lamp would move ahead and be seen by the driver of that train. Maybe no others but, certainly by the train driver.

Quite how you could measure it seems a little doubtful! As with all Inter-Stella 'suggestions' they are little more than educated guesses. People may know what 'time' is but, it is a whole different thing knowing how it and all the other theories related to it work, or 'happen' in relation to each other. Fact is we will never know.

Unless a spaceship is invented with its own universe (not likely), to take 'time in a capsule', so you would not get older inside the capsule, though you may be reaching the edge of the time-space continuum..................

Well, something like that anyway!

now THAT is a good answer!

I don't believe so. Not parallel to the direction of travel. As far as I understand relativity, nothing can travel faster than light in a vacuum, so the light coming from the headlight forward would not be visible, but light at any oblique angle from the direction of travel would be visible....?????

Well folks, please now let us discuss what happens to speed of light if tail light (instead of headlight) of that stupid train is put on when it is moving at the speed of light - & please note - this time, there are no brakes to the train & all passengers are travelling ticketless (to hell?)

our science teacher, during our high school days, while lecturing on the life of Sir Einstein, asked us, " What would happen, if you are able to run faster than the speed of light?"

He himself said, " You can see yourself running behind you!!"

So, for your question, the answer is, you cannot see the projection of light, but the light will also travel with you!

trying to understand special/ general relativity using 'common sense' is futile, because we don't see it happening around us. you really have to trust the math on this one. so unfortunately, many of the answers (including some 'good' answers) were wrong, even though they seem to make sense in newtonian mechanics (the bread and butter of engineers).

i am worried that, if someone googles this topic and arrives at this thread sometime in the future, he will definitely get mislead.

relativity is not intuitive, but it is not complicated either. to answer the original poster's question: of course the light projects forward! you, who turned on the headlight, will see it do so at none other than the speed of light.

you don't need 'external inertial observers' to tell you that, just like you don't need them in a train going 100km/h. the whole point of the theory of relativity is that everything (ie the laws of physics) 'looks and feels' the same to you no matter what your speed.

so what if external observers tell you otherwise? (and they will!) Do you stop and ask people's opinions when riding a train (or a Concorde or the space shuttle)?

you might as well call it 'theory of irrelevance', that should get a lot of confusion cleared up...

time to hit the books, people!

Did I just miss it, or has no one mentioned the Lorentz-FitzGerald contraction? When you are traveling at the speed of light, everything in front of you contracts down to an infinitely small size as if you live in a two-dimensional world -- no depth. How would the light shine out in front of you if it has no place to go; it would be like shining a light "into" a two-dimensional picture. It can't be done.

Anyway, we may someday learn that Einstein wasn't correct about everything, so there could be some basis for an explanation that light doesn't necessarily have a maximum velocity. We know practically nothing of all there is to know and understand, yet we run around declaring things as "laws". Who would have ever thought that we could stop and start light? And what about "dark matter"? Why are we constantly surprising ourselves?

Cheers.

Bill Velek

This question is not meaningful. The laws of physics only permit massless objects to move at the speed of light, so you might as well ask a mathematician "suppose 1+1=2.1...?" or perhaps ask an engineer "Suppose you have a 20 story building made of treacle...?".

If the train is travelling at fractionally under the speed of light, the light will leave the front of the train at a speed which will look like the speed of light to observers on the train and off the train. This apparent paradox is explained by the fact that velocities do not add in the obvious way when they are near the speed of light, as Einstein explained in his special theory of relativity.

Relative to you, using your clock and ruler to measure speed in your space-time frame - yes!

Well the answer is yes it does project outwards from the source and you see everything that is in front of the locomotive.

At least going by what my pea sized brain says. i am often wrong though

Remember to wear shades....

As some of you know, I love to beat dead horses, so...

An excellent reference for the student without a lot of math background can be found in Mike Fowler's lecture notes:

http://galileo.phys.virginia.edu/classes/252/home.html

SR is one of those topics so often taught so badly by bad high school teachers that it is worthwhile, if you've not taken a university modern physics class, to go through all the work. If you have a good sense of fun, you might also read Relativity VISUALIZED (No, that's an underline, not a hyperlink) by Lewis Carroll Epstein. Epstein's statements and examples are a lot nuttier than mine, and he includes some wonderful hands-on exercises.

In the meanwhile, for what it's worth, some points to consider:

In nonaccelerated frames of reference, all observers will measure the speed of light as a constant unless there is a medium involved.

In space-time any two events are separated by √(x² + y² + z² -c²t²). Thus, speed must be measured as spacelike, timelike, or a mixed regime. This is the point most often missed by teachers.

SR does not prohibit an object (no matter what its mass) from traveling faster than the speed of light relative to an observer. It does prohibit an object being accelerated to that speed by an energy source in the observer's frame and it prohibits the observer from communicating with any object traveling faster than the speed of light (although the so-called Bell's paradox is still not, IMHO, settled).

By the time you get the train to operate at the speed of light, there will be a viable solution to this problem.

similar conondrum of physics...

If a car travelling 70 MPH passes a hitch hiker, at the same time a fly in the car flies from the rear window to the front window at 5MPH, is that fly flying 75 MPH (RELATIVE to to outside observer) or is it just flying 5MPH RELATIVE to the driver of the car?

Both

thus, the "speed" of light is relative to the sentient observer?

...just how "constant" is that?

Almost turns "it" (E=MC2) into an "opinion" ("from MY point of view, that fly was only doing 5MPH" said the driver to the hitch hiker...)

also, Is a photon like the fly and the light beam it moves through comparable to the car? So don't photons move faster than the speed of light simply in their inherent impetus?.

If a train is traveling at the speed of sound, and the engineer sounds the horn, will the sound be projected ahead of the train? This we have the answer to. There will be no sound from the train until it is past.

Does the same hold true for the light at the speed of light?

Yes, I believe so. We should not be able to see a train travelling towards us at a speed exactly c (at least not before it crashes us). If we would be able to see such a train this means that the photons - that had been reflected from its front surphase - should had traveled in a speed faster than c. But, as far as we know, photons travel only at speed c (at least at normal space-time conditions).

(But don't forget: a train, spaceship or any other object with mass will never be able to travel at a speed exactly c)

A Train as a material object can not reach speed of light.

I'm going in another direction.

I think that time does not exist. It is a unit of measurement.

Just as in E=MC2, time is not in the equation.

As human beings, we need to have the concept, of a beginning and an end.

1. Yes, of course. Light speed remains as a constant regardless of the motion of the observer.

2. You are using an impossible scenario. How do you propose to get a train (or any massive physical body) up to light speed? Even atomic particles increase in mass as they approach light speed. Plus there is the problem of time dilation. At very low speeds, fighter aircraft can "shoot themselves down" by running into their own bullet stream, if they go fast enough. A totally different problem.

Actually I've never for once thougth of this. But I will answer yes. The reason is that the reflective surface of the head lamp (behind the bulb) will always converge the ligth to a point in front of the train. So, although the train and the ligth are moving at the same speed, they are not at the same position, which means the ligth will always be in front of the train

I wish I knew, but I don't. I am not even sure if any of Einstein's theories are relevant. He, as we all are, observe from a time/space perspective. When you measure the speed of light, are you actually measuring the speed of light or are you measuring your relative place in space/time to the object that emitted the light? According to Einstein, time is curved due to gravity. How can we measure anything without understanding this curving and taking it into account. Maybe one of you guys is smart enough to understand all this but I doubt it. I know I sure don't. More and more though here lately I am beginning to believe that light is instantaneous and our measurements are biased by our position and speed in space relative to the source. Help me out here. Could I be right?

Hi Keywalker. You said: "I am beginning to believe that light is instantaneous and our measurements are biased by our position and speed in space relative to the source."

Just forget it. The speed c of the light is always the same and is irrelevant of the direction, the position and the speed of the light source. And this is proven by observations and experiments.

G.K. is right. Apparently the speed of light is independent of the motion of the source. In that case, the headlights do project in front.

Einstein's special relativity states that the speed of light is constant which in essence means that the relative velocity of light remains the same as well. Which kind of makes sense right, since light is composed of photons which are more or less reflected by the body prior to reaching someones eyes. So a photon emitted/ reflected from any point would travel at the speed of light regardless.

I know Newtonian laws dont really apply to photons since they are massless and other reasons, particle and wave nature, etc... but the above interpretation seems viable to me but fails completely for some scenarios.

It really does depend on which frame of reference you use. The engineer on board the train sees the light project out. An observer standing near the track sees no light projection, but also sees no train since the length is now shrunk to zero (Well, perhaps he sees a 2D cross-section of the train rotated toward him, but that scenario is a little questionable exactly at c).

OK, let's change it a little. You're standing some distance back from the track, looking at the track perpendicularly. You see a train passing backwards at, say, 0.99c. Just at the moment he passes, he turns on his headlight. You see that light beam move at c. In other words, you see the train moving at 0.99c to the left and the light moving at c to the right. You conclude that the relative velocity between the train and the light beam is 1.99c. Is this a violation of SR?

No violaton at all. In this case nothing is really moving at a speed greater than c (relative to sth else). You see the light moving at c and the train moving at 0.99c. The driver of the train sees the light (from the headlights) moving at c too. Everything is o.k. You just get the wrong conclusion that the relative velocity between the train and the light beam is 1.99c just because you try to add or subtract the velocities in a conventional way (as we do in the case of low speeds). In the case of speeds very near to c SR gives us the right way to conceive and measure these very high speeds.

G.K.,

Thanks for the reply. But, I disagree. It is a trivial conclusion for observer c to think a and b are moving away from one another at almost 2c, but it is not wrong. There are two points to be made:

1) the speed limit is about information not objects;

2) the conclusions we draw must be about what we measure not what is (since there is no absolute is).

I can appreciate that my answer seems pedantic, as though I'm splitting hairs very finely, but that is the usual case in SR. Any statement of problem has to include information about the observers, how the measurements are made, and the frame(s) of reference.

Hi again TVP45.

About (1): c is an absolute maximum speed limit concerning either info or objects. I agree with Physicist at post#111 who says that even the existence of an object is info. Moreover this object could be a memory chip or a letter :-)

About (2): In our example what you really measure is the speed of the spaceship (0,99c) and the speed of light coming out of its back headlights (c). These are real results with respect to your reference frame. When you say that the light is travelling away from the spaceship at speed 1,99c (with respect to the spaceship) is just a conclusion (or an assumption) that you make. And I say that this conclusion is wrong because you are "talking" about another reference frame (e.g. that of the spaceship). It's like to say that: "if I was on the spaceship I should observe the light traveling away at speed 1,99c"... But the only appropriate person to talk about it is the driver of the spaceship. And he says that: "I observe the light traveling away from my spaceship at speed c"... And this is an observation (or a measurement) not just a conclusion.

G.K.,

Thanks for the reply. Yes, I agree that existence can be information (we're getting into some deep, Bill Clinton semantics here), but we do have to always say something about our particular situations. For example, if we think of the old example of the edge of a shadow, we know such an edge can move faster than c, and we can distinguish between shadow and not shadow, but is it capable of conveying any information? I would say no and assert that you have to turn the shadow on and off to convey information and that can only occur at c.

That is equivalent to confusing phase velocity and group velocity: the information on the position of the source of the shadow travels from the source at the speed of light.

Yes, I agree. I meant to make that point but may not have. Thanks.

I had never considered this before, but it seem to me that the faster the locomotive goes, the more massive it becomes until would aquire enough mass to collapse into itself and become a black hole. Then light would not get out, so the question does not make sense.

...until would aquire enough mass to collapse into itself and become a black hole.

I have the impression - someone may correct me - that the relativistic increase of mass has actually to do with an increment of the difficulty to further accelerate the mass, i.e. what is increased is the inertial mass. I doubt there are any gravitational effects due to speed.

Yes, Tkot, (I think) you are right. In this case we deal with the "inertial mass" not the "gravitational mass".

No. This is a common error, but general relativity implies that all energy creates a gravitational field (including photons, for example).

Before justifying this statement it is necessary to recall that gravity in general relativity is much more complicated than in Newton's theory. Newton's theory is a scalar theory where a scalar (mass) produces a gravitational field that requires just one parameter (a potential field). Einstein's field equations say that the curvature of space-time (a symmetric 4-tensor field) is a simple multiple of the stress-energy tensor. The (0,0)th component of the stress-energy tensor is the relativistic energy density, the (0,i)th components are the density of momentum in each spatial direction, and the (i,j)th component is the flux of i-momentum in the k-direction (i,j are 1,2,or 3). The (i,i)th components (i=1,2,3) are the components of pressure.

As a consequence massless objects like photons affect the gravitational field (since they have mass and energy), and (more relevantly to this subthread) the momentum and energy embedded in a moving object are increased because of the special relativistic effect on the apparent mass.

Hi Elroch. You said "apparent mass" and I think this is the whole issue. As you already know, when you apply energy (force) to an object in order to accelerate it, in low speeds, almost all the energy is consumed for the acceleration and just a tiny (and negligible) part of this energy is consumed for the apparent increment of its mass. The opposite happens in very high (relativistic) speeds (near c). Nevertheless, I doubt that this increment of the mass cause an increment of the gravity.

Just think of this: If there were a real and objective increment of the mass, the driver of the spaceship should, also, feel the increased gravity caused by the floor and all the other objects inside the spaceship. But he does not. He experience that everything (the time, the lengths and the mass) is as normal as usual. Only the outside observer experience such an increment of the mass.

But (I wonder) if it is so then where all this extra external energy goes (if not to increase the gravitational field)???

And what is the natural meaning of such an increment of inertia at speeds near c???

In fact, I'm not so sure that all the above are correct, as the inertial mass and gravitational mass are supposed to be the same. (I wish Jorrie could help us.)

Apparent mass was a rather old-fashioned phrase for me to use. These days, the only mass that is used in physics is the rest mass - it is the energy that increases with speed according to the laws of special relativity.

I am very confident that you are wrong to think that this extra energy has no gravitational effect, because this would completely contradict general relativity, which is one of the main generally accepted theories of physics. There is certainly evidence from astronomical observations that implies the "relativistic mass increase" increases the gravitational field.

It is not valid to say that because in the frame of the observer, the object exerts an increased gravitational field, this increased field should also be observed by the driver of the fast moving vehicle. Most measurements depend on the frame from which you measure them in relativity, and this is one of them.

The gravitational field in general relativity is, unfortunately, a complicated thing that is difficult to understand for all of us, but the tensor that describes it depends entirely on the energy and momentum in the object creating the field. So to say it doesn't would require saying that general relativity (and the observations that support it) is entirely wrong.

Hi again, Elroch. After a second (or third?) thought I tend to believe that I was initialy wrong. (You saw that, in my previous post, I had doubts concerning my first statement... and I couldn't decide what is the correct approach...)

These are my points:

1) It's wrong to make a distinction between the inertial mass and gravitational mass because (according to SR) are exactly the same.

2) We give external energy to the spaceship (trying to reach c). This means that we increase, continuously, its kinetic energy. The only difference is that at very high speeds (as we approach c) we increase the "mass" part of the equation instead of the "velocity" part, e.g. the opposite of what happens at low speeds. Anyway, this huge kinetic energy is energy (equivalent to a corresponding mass). And, like any other form of energy, it is supposed to produce (and affected by) a gravitational field.

3) This increment of mass (equivalent to this extra kinetic energy "loaded" on the spaceship) is observed, of course, only by an external observer (named A) who will sense the corresponding gravitational field. But the driver (named B) will not observe any mass increment of himself and whole spaceship. My question was "how is possible the driver not to feel any gravitational field???". And then I realised that he WILL feel a grav. field: not the grav. gield of his spaceship but the grav. field of the observer A. So B (from his point of view) will observe A to travel at speed near c and he will observe the mass increment of A and he will feel the grav. field produced by A.

So I tend to believe that you are right. But what happens if the spaceship almost reach c??? Does this mean that the spaceship will turn into a black hole as it is observed by A??? And A (and everything else) will turn into a black hole as it is observed by B??? ......

In fact, General Relativity tells us that gravity is NOT a property of mass as such, but rather an effect of the interaction between mass and spacetime. That in fact gravity and acceleration are the same thing, or at least indistinguishable. Large masses create what we call gravity by warping the structure of spacetime. The larger the mass, the greater this effect, what I like to refer to as a mass-warp.

A nice way to visualize this is to picture three dimensional space as a flat, infinitely elastic sheet, with time as the axis which extends both above and below. When a mass is "dropped in" to spacetime, it creates a depression in the structure, or fabric, of spacetime, a mass-warp. Thus, when any other free-falling mass enters this region of warped spacetime, it's path is modified towards the larger mass. Even light is subject to this. Also, this visualization demonstrates another relativistic consequence, which is that in this region of warped spacetime, time itself is distorted, which is to say, slowed down, as illustrated by the mass-warp's depression along the time axis.

Now please keep in mind that this is only an analogy, a nice way to visualize what is happening, and like all analogies, it must be treated with suspicion, as it is at best an incomplete description of what is really going on. To truly understand General Relativity requires mathematics which most of the human race (myself included) does not understand.

What is important to understand here is simply that gravity, and with that inertia, momentum and the like, are not truly properties of mass, but results of how mass interacts with the continuum.

Ah, but mass is still required - massless "objects" (say photons) don't interact the same way, hence don't exhibit gravity. They may not even experience time the same way objects with mass do, come to think of it...

I must respectfully disagree. Photons do in fact posses mass, as demonstrated by that famous equation, E=MC². Now granted, that "mass" is very slight, but it does exist. If photons were truly mass-less, they would be unaffected by gravity. As to whether a photon experiences time... At this point I confess my ignorance.

Upon further reflection, and since Professor Einstein always encouraged us to allow the formalism to speak for itself, Special Relativity seems to require that any mass moving at the speed of light must enter a state of temporal stasis. Therefore a photon, by definition, must not experience the passage of time.

Furthermore, one interesting way to look at mass is as a pocket of condensed energy, a tiny whirlpool. Again, not real accurate, but a nice analogy.

Physicists would not say a photon has mass (because these days that term is used only for rest mass) but general relativity implies that every particle with non-zero energy (which includes all photons) affects the gravitational field.

I just noticed a typo of mine in this post - I meant to say photons have momentum and energy of course. The Einstein field equations hold the answer to most of the issues discussed in this thread. It is unfortunate that they are not trivial to understand and very difficult to solve. :-)

Why put the headlights on?

Once you are travelling at the speed of light, you are a light source. Light will travel in all directions from you at the speed of light.

Unfortunately since you are travelling in one direction at the same speed, you would hit the light barrier. Everyone would see a big flash of light. It would look like a streak that represents your path.

Inside your locomotive you would not see any light from yourself since reflections could never catch up. When you stopped everyone else would glow brightly for you(afterglow), while they are blinded.

Yep, theres your super train

In response to techno

1. Nothing that has mass can reach the speed of light (as those here who know some relativity have pointed out)

2. There is no reason why something moving at the speed of light (made of massless particles other than photons) would emit light

1. Nothing that has mass can reach the speed of light

Agree, You would become pure energy. Your atoms will basically convert to energy. This would be in the form of: electricity, heat, radiation, and light.

2. There is no reason why something moving at the speed of light (made of massless particles other than photons) would emit light

Disagree. Different atoms will convert to different forms of energy. Some of your atoms would transmit light. Basically anything that you see is retransmitting absorbed light and thus given more energy will transmit more light. Other things that you don't see may still give off light given enough energy such as gases. (that is how we create street lights)

You claim to disagree with my point 2, but then address something different - the physically impossible situation where atoms move at the speed of light. They cannot, so no conclusions can be drawn about what would happen. And there is no law of physics that says that if things go very fast they will change into something else - in fact the laws say that they are independent of speed, so an atom moving very fast stays as an atom. [What happens if an atom hits something else moving at a different velocity is an entirely separate question].

OK, no conclusions can be drawn about what would happen.

This whole blog is only a theoretical, mind storm If atoms (or trains) could reach the speed of light to help understand the properties of light.

My whole theorem said that crossing that impossible speed barrier, they hit the possible "light barrier" and are converted to pure energy.

All these apply. .....sorry

It doesn't matter if the light works or not. By the time you see anything you have already run over it with the train.

Another interesting thought is that anyone in front of the train would be hit by the train at the exact instant he sees the light.

So say your train is a spaceship that utilizes the encapsulated suck and blow cocoon for multi universe warp drive transverse? Say it is that for every different universe that there is the one constant, a constant speed of light for each different universe. You would want to run your fast train of the c constant from a universe with a fast speed of light constant to a universe with a slower speed of light constant, avoiding overspeed in your universe. I could be wrong. Possibly you need to run your train to the faster universe with a different speed for light so you never catchup. I had dinner with Gene Rodenberry once. We didn't get around to Warp Drive. Anyway from what I know the only way your train going at the speed of light in this universe could have light project from it, would be if it was using a lamplight in a universe with a slower constant. (of course I allow that I could be wrong, and accept overall the experiments are difficult and or, dangerous.)

Yea, me too. I had catchup with dinner once.

Since the light is at the front of the train, the instant you turn on the light, the train will no longer be at the speed of light...the light would behave as a reverse thrust since the propelling force would be magnetic warp fields or lasers to provide a thrust velocity = to the speed of light

The propelling force must exceed the mass\inertia of the object being propelled and have a velocity equal to or greater than the velocity to be acheived.

Sapper.

Could we put two lights on the back of the train to counteract the forward light?