[dillerX]

No one has ever been able to answer this question for me. If you were traveling at the speed of light, and turned your headlights on, what would happen?

[L'enfanTerrible]

Everything would stay dark, because you would be travelling at exactly the same speed as the light from the headlights, so they wouldn't reflect off anything......


possibly

[BRussell]

I think the speed of light is a constant, so the light from the headlights would travel from you at the speed of light. It doesn't matter how fast you're going.

[flatcatch]

Originally posted by L'enfanTerrible:
Everything would stay dark, because you would be travelling at exactly the same speed as the light from the headlights, so they wouldn't reflect off anything......


possibly

What he said. The light would never have a chance to move out in front of you since you are speeding along just as quickly.

[flatcatch]

Originally posted by BRussell:
I think the speed of light is a constant, so the light from the headlights would travel from you at the speed of light. It doesn't matter how fast you're going.

... but wouldn't that imply the light from his headlights would need to be traveling at twice the speed of light?

[dillerX]

perplexing it is.....

[malvolio]

Originally posted by flatcatch:

... but wouldn't that imply the light from his headlights would need to be traveling at twice the speed of light?

Darling! Call NASA!! I just had a brilliant idea!!!

[flatcatch]

We'll just clear it up right now:

The car's headlights would shine, but light can't move faster than the speed of light--the car would run into it! So a driver in the car wouldn't see any headlights. Also, because of the motion of the car, the light would be blue-shifted (infinitely) for someone standing in front of the car--instead of white light, the light would be stronger than x-rays or gamma rays! (David Knobles, Ph.D., Department of Physics, The University of Texas at Austin, Texas)

- David Knobles, Ph.D., Department of Physics, The University of Texas at Austin, Texas

http://www.nsf.gov/nstw_questions/phys/quest013.htm

[BlackGriffen]

Originally posted by flatcatch:


... but wouldn't that imply the light from his headlights would need to be traveling at twice the speed of light?

With respect to what? Two problems: one, nothing with mass can ever go the speed of light (that would require infinite kinetic energy/momentum), so the best you could do is annihilate yourself in a matter antimatter reaction (changing all of your matter in to photons), but then you won't be you; two, you're applying a Galilean transformation to a relativistic phenomenon. There are two rules in special relativity: one, all inertial (i.e. non-accelerating) reference frames are equally valid; two, light always moves at the speed of light, no matter who is observing it, the observers will simply disagree on the wavelengths of the photons. So suppose you see someone coming at you very close to the speed of light. They turn on a flashlight, and it looks blue to you. They keep this flashlight on you as they pass, and it appears to change to red as they zoom away (note that this is partially the doppler effect, but there are also length and time transformations involved that ensures that you will be unable to find a special frame of reference for the light). The light will bridge the gap between you at c at all times. That is one frame of reference and one point of view. From the point of view of the other guy, somebody is zooming past him at very near c, and he's using his yellow flashlight to warn you not to hit him.

BlackGriffen

[BlackGriffen]

Originally posted by flatcatch:
We'll just clear it up right now:

The car's headlights would shine, but light can't move faster than the speed of light--the car would run into it! So a driver in the car wouldn't see any headlights. Also, because of the motion of the car, the light would be blue-shifted (infinitely) for someone standing in front of the car--instead of white light, the light would be stronger than x-rays or gamma rays! (David Knobles, Ph.D., Department of Physics, The University of Texas at Austin, Texas)

- David Knobles, Ph.D., Department of Physics, The University of Texas at Austin, Texas

http://www.nsf.gov/nstw_questions/phys/quest013.htm

That's nice, but it's an argumentum ad vericundium (appeal to authority). What do those three letters after his name mean? Piled higher and Deeper, right?

Simply put, it only makes sense to have a reference frame if there is mass in it, and since mass cannot go the speed of light, the question is moot. If you watch in the limit as the car gets closer and closer, this is what you'll find:

from your point of view: the car will undergo a length contraction and appear to be short and squat. Between the double whammy of the length contraction and the doppler effect, the headlights with increase in frequency divergently (a.k.a. at c there is a divide by zero in the equation). Again, at c the question becomes moot because the photons would have infinite frequency, and thus have infinite energy (note: not possible). Assuming the light was shining in all directions, as soon as he passed, the frequency would go to zero (a.k.a. you couldn't see any photons). This "headlight effect" can actually be observed in electrons that are accelerating and have high velocity (in their own frame, they're radiating photons outward in all directions, in the lab the photons appear to be shining out of the front of the electron, like it had a headlight). Note that the headlight effect would also mean that the beam of light would have diameter zero (again, warning you that there is something screwing going on with the situation posited).

From the guy in the car's point of view: he's just sitting there with his lights on while some weird-o who likes to ask nonsensical questions whizzes by . (just ribbin' ya).

Another way to put it that I just thought up:

The postulates say that all reference frames are equal and that light moves at c in all of them, right? Naturally someone would ask, "Well what does the light see?" Good question, as you accelerate in an attempt to put yourself in the reference frame of the photon (you're accelerating in the same direction as a beam of light travels), it gradually dies out as it's frequency drops. Thus, there is no frame of reference where the photon is at rest because as you move faster, the light is disappearing (vanishing completely if you could somehow magically set your speed to c). Thus light does not have a frame of reference. Combine that with the fact that it would take infinite energy for an object with any mass to accelerate to the speed of light (with respect to the original frame of reference), and you find that the conundrum isn't a problem it all. It would be kind of like asking, "Would I be sucked out if the sky split open?"

BlackGriffen

Edit: cleared up a sentence, added last note on headlight effect.

[arrested502]

I like the "something really scientific would happen" answer

It's nice and "safe".

[G4ME]

E=MC^2

C=?E/M

seeming that the speed of lightn is 3x10^8 M/S means that to travle that fast you would have to take the ? of all the energy in the universe and divide by all the mass in the universe so thats imposible.

can't happen

[BlackGriffen]

Originally posted by G4ME:
E=MC^2

C=?E/M

seeming that the speed of lightn is 3x10^8 M/S means that to travle that fast you would have to take the ? of all the energy in the universe and divide by all the mass in the universe so thats imposible.

can't happen

Funny, but no. The E in that equation is the rest mass energy (i.e. the energy inherent to a mass at rest). The correct equations are:

• E = γmc^2 (where E = total energy, m = mass, c = speed of light)
• p = γmv (where v = velocity [the vector])
• γ = 1/√(1 - (v/c)^2) (where v = |v|)

BlackGriffen

Edit: added √
Edit2: fixed E equation, the original was kinetic energy.

[sambeau]

I reckon you're eyes would pop and the goo would run all down you're face. Then you're whole body would be pulled into an infinitely long piece of spaghetti and your toes would all curl up or something.

It probably wouldn't hurt though as electrons also move at the speed of light so your nerves would stop working.

or something..

[Tigerabbit]

Originally posted by BlackGriffen:
so the best you could do is annihilate yourself in a matter antimatter reaction

Sounds like a plan. I volunteer Ca$h for the experiment.

[sambeau]

Originally posted by BlackGriffen:



the best you could do is annihilate yourself in a matter antimatter reaction

what would happen if pasta ever met antipasta?

[G4ME]

Originally posted by BlackGriffen:


Funny, but no. The E in that equation is the rest mass energy (i.e. the energy inherent to a mass at rest). The correct equations are:

• E = γmc^2 (where E = total energy, m = mass, c = speed of light)
• p = γmv (where v = velocity [the vector])
• γ = 1/√(1 - (v/c)^2) (where v = |v|)

BlackGriffen

Edit: added √
Edit2: fixed E equation, the original was kinetic energy.

yeah I was just trying to sound smart Haha

[rambo47]

Two points to ponder:

1) Researchers claim to have slowed down light to under 50 mph in some kind of refraction experiment. I believe it was at Princeton, but I'm not sure.

2) Astronomers have observed a gas jets at a suspected black hole where the gas spewing away was moving at a speed faster than light.

Sorry I don't have links to sources. These were headlines on the science section of my Excite start page a while back. Anybody have links?

[sambeau]

Originally posted by rambo47:
Two points to ponder:

1) Researchers claim to have slowed down light to under 50 mph in some kind of refraction experiment. I believe it was at Princeton, but I'm not sure.

2) Astronomers have observed a gas jets at a suspected black hole where the gas spewing away was moving at a speed faster than light.

Sorry I don't have links to sources. These were headlines on the science section of my Excite start page a while back. Anybody have links?

Dunno about the first one, but the second one is due to teleportation and the uncertainty principal. Photons can't be pinned down to one place exactly, just an average spot. Hence light can travel faster than lightspeed at times and escape from the edge of a black hole.

[fat mac moron]

Man, I thought Slashdot was bad

[juanvaldes]

stupid deer, always getting in my way...

[BlackGriffen]

Originally posted by rambo47:
Two points to ponder:

1) Researchers claim to have slowed down light to under 50 mph in some kind of refraction experiment. I believe it was at Princeton, but I'm not sure.

2) Astronomers have observed a gas jets at a suspected black hole where the gas spewing away was moving at a speed faster than light.

Sorry I don't have links to sources. These were headlines on the science section of my Excite start page a while back. Anybody have links?

It's worth noting that the speed of light is the speed of light in a vacuum. It is possible to slow light down. For instance, nuclear reactors have a blue glow in the water around them. The blue glow is caused by particles (neutrons or electrons, I can't recall which) exceeding the speed of light in water, and so something funky happens (I thinks it's the equivalent of an optical sonic boom, but I'm not sure). Also, diamonds sparkle in that special way because they have a very high index of refraction (the speed of light in a vacuum divided by the speed of light in the medium in question).

BlackGriffen

[iNub]

Einstein's theory of special relativity, Maxim style:

Originally printed in Maxim, February 2002

Special Relativity

We know motion is relative--you can only tell you're "moving" by comparing yourself to another object--and that that speed of light is the fastest speed there is. So here's the inevitable question: If you're going the seed of light and hold a mirror in front of your face, would you see your reflection?

You'll need:

• Bette Midler
• A rocket traveling the speed of light
• A mirror
• A shaving kit
• Several bandages
• The Olsen twins

[list=1][*]Board the light-speed rocket, then send Bette Midler into the cubicle batrhoom to shave her chin. Away from any reference point, she has not idea she's actually moving her razor at the speed of light--relative to the ground, not her stubble.[*]Have Better look in the forward mirror. If she sees her reflection, the light must be moving faster to get to the mirror--and light can't go beyond it's maximum speed. But if she doesn't, then light would have a speed of zero relative to her. So...[*]Eistein's answer: She sees her reflection (and the speed of light stays constant) because accelerating close to the speed of light actually causes time itself to slow down and distances to shorten. Hey, stop hogging the bowl, man![*]Cut to Mary-Kate Olsen heaving in a barf bag. Her watch is moving normally, but after three hours at close to* the speed of light, 242 years have elapsed for us. So Mary-Kate's still criminally underage, while Ashley, back on Earth, has turned to ash.[/list=1]

*How close? 99.99999999999%

[iNub]

Ah, what the hell.

Originally printed in Maxim, February 2002

General Relativity

He had special relativity, but Albert "Afro before it was cool" Einstein wonderd if gravity could be worked in. So he did it.

You'll need:

• Carson Daly
• An elevator
• Cable cutters
• A bathroom scale
• Two watches
• Brutal, murderous resolve

[list=1][*]Have Carson Daly get in the elevator and accelerate it upward. Since acceleration has the same effect as gravity, he'll weigh more as he speeds up. When he reaches 9.8 meters per second^2(same as the pull of gravity) he'll weigh twice as much as his normal chunky ass.[*]Now synchronize your watch to Daly's, then cut the elevator cable. As sthe elevator acceelrates (downward this time), Carson's weight relative to the elevator becomes less ad less until he seems to weigh nothing, happily floating inside the car.[*]...until he smashes to a bloody pulp at the bottom of the shaft. Although Carson felt weightless, his weight relative to the earth was unchanged, and he was subject to gravity accelerating him downward at 9.8 meters per second^2. Hence his graphic, but hardly tragic, demise.[*]Pull out Carson's severed arm and compare your watch to his. Gravity caused the same time distortion as Bette's rocket; when carson weighed more, time moved more slowly for him, making his watch slightly behind yours. Feel free to keep it as a souvenir.[/list=1]

3. Catch Phrases

Learn these terms ad become the king of any geek cocktail party!

E=MC^2
Mass has energy, and energy has mass. Einstein devised formulas to quantify why nothing could ever exceed the speed of light. Along the way he came up with the most famous equation in history, E=MC^2, showing that mass and energy are interchangeable. We know energy has mass because a spring weighs slightly more coiled (with potential energy) than uncoiled. As for mass having energy? See Bomb, nuclear fricking

Black Holes
A star more than 1.5 times the mass of the sun when cold will eventually collapse in on itself to form a black hole, sucking all kinds of energy--even light--into it. Black holes are defined by their boundary of no return, called the event horizon, where intense gravity slows time to a crawl. If you were watching an astronaut fall into a black hole, he would freeze at the event horizon for eons; if he could look back, the future history of the universe would pass in a flash before he turned into spaghetti.

Gravitational Lens
Supermassive objects can have gravity fields so intense they actually cause light to bend and intensify as it tries to sneak by them, creating what's called a gravitational lens. This magnifies faraway objects, allowing us to see certain far reaches of the univers.

Wormholes
Supermassive objects (like black holes) that are close together could produce a gravity field so strong that a time-space curl called a wormhole will apear, according to Stephen Hawking and other folks too smart for us to question. Given a big enough wormhold, larger objects,--like us, even--could use them to travel through time.

[dillerX]

Ahh, I love comedy at 4:15AM.

[Sven G]

Engineer's answer: how did you build a machine capable of travelling at the speed of light?

[dillerX]

Originally posted by Sven G:
Engineer's answer: how did you build a machine capable of travelling at the speed of light?

CIA's answer: If we told you we'd have to kill you."

[Cipher13]

I haven't read all of this, but has anyone mentioned the doppler effect? Blue/red shift?

On a simple scale, you'd be travelling at the same speed as the light, therefore nullifying any visual effect.

However, the doppler shift, bunching the waves together, while not increasing their speed necessarily (oscillation unaffected? I dunno... would they remain lightwaves under their new conditions?) would project them further from the body of the car... it's hard to explain this late at night when you haven't slept. Somebody knows what I mean, I'm sure. So in the end, there may be a small visible spot.

I dunno. I'm a geneticist, not a physicist.

[Cipher13]

Actually, some of the effects I mentioned would never have the chance to manifest - given the speed of the vessel when the lights are switched on, the waves would never have the chance to escape any significant distance. If the lights were switched on while proxiluminous, and *then* the vessel accelerated to c, that might be relevant.

It seems the general consensus is "something really scientific would happen", either way

[BlackGriffen]

Originally posted by iNub:
2. Have Better look in the forward mirror. If she sees her reflection, the light must be moving faster to get to the mirror--and light can't go beyond it's maximum speed. But if she doesn't, then light would have a speed of zero relative to her. So...

Bzzzzt! Wrong, and thank you for playing. Parallel velocities don't add linearly, they add like this:

V' = (V - U')/(1 - V*U'/c^2)

Where V' is the velocity in the new frame, V is the velocity in the old frame, and U' is the velocity of the new frame compared to the old. Note that this equation only works if all the velocities are parallel. There are other transformations for when the velocities aren't parallel, but I don't want to bother with them right now because I don't have access to html to do subscripts and such.

BlackGriffen

[BlackGriffen]

Originally posted by Cipher13:
Actually, some of the effects I mentioned would never have the chance to manifest - given the speed of the vessel when the lights are switched on, the waves would never have the chance to escape any significant distance. If the lights were switched on while proxiluminous, and *then* the vessel accelerated to c, that might be relevant.

It seems the general consensus is "something really scientific would happen", either way

I thought I had already explained all of this, let me list the problems:

• the car would have length zero, because of length contraction, and thus so would the light waves (very problematic because in order to have length 0, they have to have infinite energy)
• The car's time will have stopped for the outside observer. So it wouldn't be possible to see the car "turn something on" and have someone outside of the car observe it (from the car's point of view, your time has stopped, and thus you cannot observe it).
• The "headlight effect" (very real and observable) would mean that any light whatsoever coming from the car would be squished in to an beam pointing forward with 0 width.

Okay, let's dig a little deeper now. First of all, you would all agree that we're moving forward through time, right? Well, time and space are both literally the same type of dimension (in relativity). When you accelerate, you are simply rotating which direction you call time in four dimensional space so that it points in a different direction, and what you once observed as time, you will now see as space. In order to "travel at the speed of light" your time line would have to be perpendicular to the old one. Thus, to quote Men in Black, "You wouldn't even be matter," from the old frame's point of view. It is theoretically possible, taking this point of view, to rotate your timeline 180 degrees (and thus "travel backwards in time), but how you would accomplish that is no easy question to answer since it would require two 90 degree rotations, and we can't even do those. Not to mention the fact that it takes up space to do all of this, and thus best you would do (assuming instantaneous 90 degree rotations) would probably be to arrive the moment you left (a.k.a. you would "move in a circle"). I haven't actually done the calculations for this, since I haven't studied general relativity yet, so take what I've said in the timeline rotations section with a grain of salt.

Is it any clearer now?

For further reading, I recommend Brian Greene's The Elegant Universe. It's a book about string theory that is good because of its non-mathematical introductions to quantum mechanics and relativity in the front.

BlackGriffen

[denim]

Originally posted by sambeau:
what would happen if pasta ever met antipasta?

Finally, a decent question!

I thought that was spelled "antipasto", not so?

[denim]

Originally posted by BlackGriffen:
For instance, nuclear reactors have a blue glow in the water around them. The blue glow is caused by particles (neutrons or electrons, I can't recall which) exceeding the speed of light in water, and so something funky happens (I thinks it's the equivalent of an optical sonic boom, but I'm not sure).

I would have thought of it as more like how a particle such as a parachutist sans parachute makes a mess on hitting the ground.

It's called "cerenkov radiation" and is caused by beta particles moving at the speed of light hitting another medium, water in this case, and changing speed. You got the right idea. Gives off a purple glow; I've seen it.

[shanraghan]

I think this question is made much easier if we just assume we CANNOT go the speed of light. After all, it is technically impossible.

At any rate, even at speeds that come very close to c, the headlights would still turn on and act normally, as the speed of light must be c in all frames no matter how they are moving relative to other objects or the light source. However, at the speed of light I'm uncertain as to what happens. Let's just say wierd thing happens when time stops... I assume...

[Hinson]

Originally posted by BlackGriffen:


- David Knobles, Ph.D., Department of Physics, The University of Texas at Austin, Texas


That's nice, but it's an argumentum ad vericundium (appeal to authority). What do those three letters after his name mean? Piled higher and Deeper, right?

Simply put, it only makes sense to have a reference frame if there is mass in it, and since mass cannot go the speed of light, the question is moot. If you watch in the limit as the car gets closer and closer, this is what you'll find:...

As another person with a Physics Ph.D., I'll second BlackGriffen's general comments. The speed of light is not a valid frame of reference for an observer in this context.


-Jay