Large Hardon Collider

[Eliseos]

Nope, special relativity kicks in then. If you are the person traveling close to the speed of light and turn on your headlights, it would appear light travels the normal speed it does from your perspective. An observer standing still in reference to you would see relativistic effects, but would never measure the light traveling faster than c.

[Woozie]

What would happen if you were traveling at the speed of light, and then turned on your headlights? Is that even possible?

I know if your driving your car at say, 120mph during a high speed shoot out, and then fire your gun, you get the velocity plus that extra 120mph or something like that... I'm curious if it's possible with light. Would that be considered FTL?

Light is really tricky. If you're traveling 120mph and throw a ball 5mph, then the ball actually travels 125mph, the balls original speed plus the "boost" it gets from being a part of the car's system.

Light never receives such a boost.

Let's say I'm on the ground and Eliseos drives by in a car going 60mph. If he's holding a ball, then I measure the ball as going 60mph. He measures the ball going 0 mph because he's holding it so compared to him, it's not moving. Think about any time you've ever driven a car. To you, it looks as if your passengers are sitting still and everything else outside of you appears to be moving backwards at negative 60 (or however fast you're going).

So anyways, I measure Eli's speed at 60. I measure the ball at 60. Eli measures the ball at zero and me at -60.

Let's say Eli throws the ball forward 5 mph (from his point of view). Then from my point of view, it appears the ball is going 65mph.

So which of us are correct? Well, the laws of physics are identical in both frames as long as neither of us are accelerating. So there's no way (even in principle) we can do an experiment to determine who's wrong and who's right. So we're either both right or both wrong. In other words, are points of view are exactly equivalent.

So, anyways, since the speed of light goes at a speed which we call "c" (300,000km/s), then if he's in a car and turns his headlights on, this is what we would expect based on the ball analogy:

Eli measures the light to go at speed c

I measure the light to go 60mph + c.

In actuality, it doesn't happen this way. Instead, we both measure the light to go at the exact same speed. I measure it to go c, and he measures the same beam of light to go c. It doesn't matter that he's moving 60mph faster than I. Our motion does not matter in any way whatsoever. No matter what the situation is, we'll both always measure light to go at c. Never any faster or never any slower.

Even if he was going 99.999999999% the speed of light, he would still measure the light to go c (not c + 99%). It would be kind of odd, if you think about it. I'd measure the beam of light as going only slightly faster than him (because I measure him to be going .9999999999*c and the light to be going c). So I'd see the beam of light slowly inch ahead of him. Kind of like how if a car goes 55 mph and another goes 56, we see one inch slightly ahead of the other.

Eli, observing the same beam of light, would see it shoot waaaaaaaaaaaay ahead of him instead of slowly inching past him.

The reason things come out this way, in a way that's so contradictory to our common sense notions is because our "common sense" is empirical (or at least in this subject. Philosophers argue whether or not it's all empirical or if some of it is truly innate). In your post, you indicated that if you shot a gun while in a car going 120mph, the bullet would get a 120mph boost. This reasoning is based on events we see around us. At speeds much lower than the speed of light, this type of reasoning is almost exactly correct. We see this, and we base our common sense off of this. So then when someone tells you that light will always travel the same speed no matter what your point of view is, it seems like what they're saying violates common sense. But it only seems that way because our common sense is based on the assumption that what we see around us is correct, when in reality, what we see around us is nothing more than a really good approximation.

Edit: Oh, and thanks for answering my question, guys. And thanks for the article, Miz.

[Mizango]

Anytime man, glad I could return the favor seeing as how you've answered hundreds of questions for me

Seconding Fabric of The Cosmos btw, if you like Elegant Universe especially you'll enjoy it, then it depends if you like Smolin's writing style as to whether you'd like The Trouble With Physics and whatnot, good book though.

^ Yessir. The trouble with physics was actually a really good read. Three roads to quantum gravity was the one that was sort of 'boring' for the lack of a better word, but Smolin is an otherwise sharp guy.

[Woozie]

Oh yeah, Fabric of the Cosmos is awesome. Also, it's one of the few books written for laymen that does a good job explaining entropy.

Also, "The End of Physics" by David Lindley. Though, since you're not into particle physics you probably wont like it as much as I did.

Sorry Sath, but I wont get to your PM tonight. Hot chick again.

[BerenTebogo]

Oh yeah, Fabric of the Cosmos is awesome. Also, it's one of the few books written for laymen that does a good job explaining entropy.

Also, "The End of Physics" by David Lindley. Though, since you're not into particle physics you probably wont like it as much as I did.

Sorry Sath, but I wont get to your PM tonight. Hot chick again.

No problem, I actually was up to about 5am discussing it with Kaylia last night once he stopped playing lolwow. I think I've been able to reconcile part of one of my biggest ideological differences by expanding "flat" to basically just mean "any structure or shape that can bend or curve in any direction so long as it never completes a circuit creating a closed structure."

I still would like your opinion on everything though, as there's a lot I'm very touch and go on in my understanding.

[Kaylia]

What would happen if you were traveling at the speed of light, and then turned on your headlights? Is that even possible?

I know if your driving your car at say, 120mph during a high speed shoot out, and then fire your gun, you get the velocity plus that extra 120mph or something like that... I'm curious if it's possible with light. Would that be considered FTL?

Woozie covered it already, but I will try to explain it differently.


How fast is the Earth moving around the Sun? How fast is the sun moving through the galaxy? How fast is the galaxy moving in the universe? If everything is in movement, it mean certain part of the universe would move slowly, while other would move very quickly. Because of this, we should observe differents phenomena in different directions. However, it's not the case, the universe is [look] the same everywhere.

If want to have the same physics laws everywhere in the universe, the concept of speed need to generalized. You can't work in absolute speed anymore, because the speed is relative to an object you pick arbitrarily (typically the ground on Earth, but in space, which object is the zero speed ?). I will skip the whole reasoning, but one implication to preserve physics laws is that light travel at the same speed everywhere.

If you calculate the speed on light standing still, it would be 300 000 km/s. If you calculate the speed of light inside a space shuttle that is moving away from Earth at 200 000 km/s, you would still obtain a a speed of 300 000 km/s. Basically, "you" are always moving at 0 km/s, and the light always moves at 300 000km/s.



Woozie already covered an example of special relativity, and if you are curious how it works, you could also read wiki entry on relativity (it's well written and simple imo)
http://en.wikipedia.org/wiki/Introdu...ial_relativity



Now to answer your question directly. What would happen if you were traveling at the speed of light, and then turned on your headlights? It's not possible since you can't travel at the speed of light.


If you meant "close to the speed of light", then for the person inside the car, nothing would change. For someone on Earth who look at him, the light emitted by the car would be dilated and would turn red (or blue) according to doppler effect, depending of the direction he is taking.

[Eliseos]

With all that name-dropping, I must ask for my royalty fees.

We're doing some basic intro to field theory stuff next week in mechanics, I'm pretty excited.

[Mizango]

With all that name-dropping, I must ask for my royalty fees.

lol

We're doing some basic intro to field theory stuff next week in mechanics, I'm pretty excited.

Ooooooh nice. Be sure to keep us updated on how you like it and what you guys are covering.

[Max™]

Had a board that used to bring that point up constantly, regarding traveling at 99.99999~% of c and measuring the speed of light.

You're moving through time slower, so every "second" that you measure the distance a beam of light covering in your reference frame is more than a second in a frame which is not moving as rapidly.

If both frames are co-moving (i.e. can not distinguish one as accelerating or not) then they will claim symmetrical dilation for the opposite frame, any deviation from symmetry will make it possible to distinguish which is experiencing time dilation, negating the paradox portion of the "twin paradox".

http://www.euclideanrelativity.com/s...d/dilation.gif





http://www.euclideanrelativity.com/s...pythagoras.gif

[Mizango]

Since Max mentioned it, go and check out the twin paradox, its really cool and is an easy concept to grasp.

[Max™]

Obviously, I grasped it after all!

No, srsly though, see if you can figure out what breaks the symmetry.

[BerenTebogo]

Obviously, I grasped it after all!

No, srsly though, see if you can figure out what breaks the symmetry.

They can never appreciate the symmetry since any attempt to convey the symmetry will not be subjected to the same rules? (radio waves, etc)

[Max™]

Good instinct, but no, that is part of the relativity of simultaneity, and would still appear symmetrical from appropriately selected reference frames.

If the two twins passed each other from a distance they could convey the symmetry.


The point where one twin turns around and heads back is when one of them can claim the other was definitely moving, and undergoing actual (rather than apparent) time dilation.

[BerenTebogo]

Good instinct, but no, that is part of the relativity of simultaneity, and would still appear symmetrical from appropriately selected reference frames.

If the two twins passed each other from a distance they could convey the symmetry.


The point where one twin turns around and heads back is when one of them can claim the other was definitely moving, and undergoing actual (rather than apparent) time dilation.

The only way they'd be able to turn around and move back would be by breaking force-free motion and then be obviously breaking any notion of relative motion. I'm not sure that actually breaks any paradox as much as it is just a caveat.

Any change in direction, for whatever reason, would break the symmetry. Or at least that's how I understand it.

[Max™]

Yup, any change in direction is an acceleration, and SR based paradoxes only hold in situations where acceleration is not present.

After that point you swap to GR, and distinguishable frames of reference.

[Tyche]

My first attempt at Astrophotography. This is a 30 second exposure, it's a bit soft. Took it on the roof of my house and it was a bit windy and no real place to stabilize the tripod. Going to get back out and drive out of town tonight and try a few more.

http://farm5.static.flickr.com/4035/...24f5e292_o.jpg

[Woozie]

How good is the view in your area? I mean, is it a big city with a lot of light pollution or do you have a good view from a nice, dark area?

One day I'm going to just drive out to the country with a telescope just too see the view without any city lights.

[Tyche]

Relatively small town, about 30000 people. Little light polution. It could be better though, I live in town so I'm going to drive out and hopefully get a nice spot to setup and get some sharp images. Goin to bring lenses from 18 to 250mm. I read that when shooting at high zooms for long exposures that you'll get light streak from the earths rotation after about 30 seconds. We'll see how it
goes.

[Tyche]

Round 2!
http://farm5.static.flickr.com/4023/...58ac1fc9_o.jpg

http://farm5.static.flickr.com/4069/...bef5f618_o.jpg

[Eliseos]

Wow, I am jealous of the view you get. Have to drive out at least 50 miles from here to get a view like that. The farmhouse shot you have is fucking awesome.