Some Questions About Light

[GrandMasterK]

1.If I'm on a train that is moving along at the speed of light or a couple hundred miles an hour under, if I shot a gun what would happen?

 

Would the bullet not fire? Would it in fact do what bullets do which is come out of the gun at over 1,000MPH + whatever speed your traveling?

 

2. What's the force behind light? why does it move, what makes it move, why can we slow it down but not speed it up? Is it a wave or a particle? (I dont fully understand how waves work).

 

3. Why is the speed of light the determining factor on the limit in speed? For instance, if light was only as fast as 1MPH, we wouldn't be able to move faster then 1MPH right? Why is that is my question.

 

Is there any reason to think the way things move is in a fixed ratio of the speed of light? For instance, light goes 669,000,000MPH, so lets compare it to an object that moves 66,900,000MPH. In a universe where light only moves 10MPH, would that object move 1MPH?

 

4. If it takes all the energy in the universe to have enough force to move something at the speed of light, why does light move as fast as it does? My guess is that it's weightless but then that confuses me towards light slowing down in different mediums. Atleast, I take it, you cant outrun light in any medium?

[RoyLennigan]

1.If I'm on a train that is moving along at the speed of light or a couple hundred miles an hour under' date=' if I shot a gun what would happen?

 

Would the bullet not fire? Would it in fact do what bullets do which is come out of the gun at over 1,000MPH + whatever speed your traveling?[/quote']

 

under the laws that modern physics has learned, it would be impossible to do any of this so the question is moot.

 

2. What's the force behind light? why does it move, what makes it move, why can we slow it down but not speed it up? Is it a wave or a particle? (I dont fully understand how waves work).

 

i'm not sure if we understand the force behind light. photons are created when one or more energized electrons move down in orbital levels around the atom. the distance the electron falls matches the frequency of the photon emitted.

 

the reason we can 'slow light down' is because we can make it travel through mediums other than a vacuum. light is constant in a vacuum, the speed is c. but when travelling through water, or glass, or other objects, the speed is slower. it is by changing the medium that we slow photons down.

 

3. Why is the speed of light the determining factor on the limit in speed? For instance, if light was only as fast as 1MPH, we wouldn't be able to move faster then 1MPH right? Why is that is my question.

 

photons have a mass of zero (as do hypothetical gravitons). there is nothing lighter than it. there might possibly be negative mass particles, but they havent been found. because it has a mass of zero, and zero is the least mass in the universe (that we know of) then it makes sense that nothing can go faster than it. einstein shows us that as you approach c, the speed of light in a vacuum, your mass gets infinitely larger and you will therefore need an infinite amount of thrust to propel you faster. this is obviously impossible (at our current comprehension).

 

Is there any reason to think the way things move is in a fixed ratio of the speed of light? For instance, light goes 669,000,000MPH, so lets compare it to an object that moves 66,900,000MPH. In a universe where light only moves 10MPH, would that object move 1MPH?

 

i don't see the relevance of the question. i would think that, logically, all movement is at a fixed ratio to the speed of light. the greater the mass, the more force is needed to propel it.

 

4. If it takes all the energy in the universe to have enough force to move something at the speed of light, why does light move as fast as it does? My guess is that it's weightless but then that confuses me towards light slowing down in different mediums. Atleast, I take it, you cant outrun light in any medium?

 

you are right that photons do not have any mass. it takes in infinite amount of energy (not the same as all the energy in the universe) to push something at the speed of light. as the speed of an object increases, so does its relatavistic mass. the greater the mass, the more energy is needed to push it. photons are massless, so they always travel at the speed of light, they can't travel any slower or any faster. but light travels at different speeds through different mediums, and the fastest through a vacuum. i would imagine this means nothing can travel faster than light through the same medium, but i am not sure about this.

[aommaster]

I hope you don't mind me asking. But I was told that if you were able to travel faster than the speed of light, you would travel back in time. Is this true? And does this have anything to do with time dilation?

[GrandMasterK]

Thanks Roy, there's no concievable way of making even a photon move faster in a vacuum? What's Star Trek and Star Wars' excuse?

 

I saw in a magazine once (think it was scientific american) about negative particles, anti something or others? If those exist would they have a negative mass and give reason to believe they can go faster then the speed of light or is it one of those things that dont exactly exist in the universe and even if they did you just cant prove that their there (like dark matter)?

 

I don't know what a graviton is, hopefully I'll be able to find it in a thread.

[aommaster]

Hehe... and what's Star trek's excuse for sound of explosions?

 

I haven't really heard of neegative particles. As for the anti-something you were talking about, could it be anti-matter?

 

If it is, no. Anti-matter has the same properties of normal matter, such as mass, only that it has a negative charge. Also, when antimatter and matter meet, they annihilate each otehr and produce gamma waves as a result...which can then bring up the question, why is there more matter than antimatter, since when matter is created, anti matter, too, is created

 

The graviton, scientists have not yet been able to detect, although they think it exists. Scientists saw that for every one of the other three fundamental interactions, there was an exchange particle involve, a particle that was created momentarily till the interaction was over, and then disappeard. For the strong force, it was the gluon. For the weak force, it was the W+ ,W- ,and Z0 . As for electromagnetic interaction, it was the photon. They think that gravitation, the last of the four fundamental interaction, has an exchange particle called the graviton.

 

Hope that helps

[aommaster]

Sorry, double post

[GrandMasterK]

Another quick question, do we have a measurement for the force of gravity? I was just curious how much force it takes for a black hole to suck in light and about how fast it sucks things in. For instance, humans get pulled down to earth at like 130MPH or so? how fast would I get pulled into a black hole?

[aommaster]

If you really love maths, take a look:

http://en.wikipedia.org/wiki/Gravity#Newton.27s_law_of_universal_gravitation

[Severian]

1.If I'm on a train that is moving along at the speed of light or a couple hundred miles an hour under' date=' if I shot a gun what would happen?

 

Would the bullet not fire? Would it in fact do what bullets do which is come out of the gun at over 1,000MPH + whatever speed your traveling?

[/quote']

 

It would fire like normal and you wouldn't see any difference to firing it normally.

 

2. What's the force behind light? why does it move, what makes it move, why can we slow it down but not speed it up? Is it a wave or a particle? (I dont fully understand how waves work).

 

Moving is its natural state. Remember, even Newton knew this - we only need a force if we want to accelerate it, but the speed of light is constant, so no force required. We can't really slow light down - often it is claimed that we can, because light travels through media at speeds <c, but this is a bit of a fake. What is really happening is the particles in the media are absorbing the light and re-emitting it again, and this takes time delaying the light. But between emission and absorption it is travelling at c.

 

Also, it is a particle (the photon) and a wave at the same time.

 

3. Why is the speed of light the determining factor on the limit in speed? For instance, if light was only as fast as 1MPH, we wouldn't be able to move faster then 1MPH right? Why is that is my question.

 

The speed of light itself is not a limiting velocity. There is a limiting velocity called 'c' and it just so happens that if something has zero mass then it will travel at this limiting velocity. The photon has zero mass, but then so does the gluon and the graviton. We could have called c 'the speed of gravity'.

 

Is there any reason to think the way things move is in a fixed ratio of the speed of light? For instance, light goes 669,000,000MPH, so lets compare it to an object that moves 66,900,000MPH. In a universe where light only moves 10MPH, would that object move 1MPH?

 

I am not sure what you are asking here...

 

4. If it takes all the energy in the universe to have enough force to move something at the speed of light, why does light move as fast as it does? My guess is that it's weightless but then that confuses me towards light slowing down in different mediums. Atleast, I take it, you cant outrun light in any medium?

 

This should have been explained by my earlier answers.

[GrandMasterK]

Lol math is my worst subject, I dont understand any of that. Equations terrify me.

 

Dont Star Trek or Star Wars or something have something to do with hyperspace travel. Got no idea what hyperspace even is, all I know is stars move by unrealistically fast and they never run into them.

[GrandMasterK]

It would fire like normal and you wouldn't see any difference to firing it normally

 

But if it did, wouldn't it be going faster then the speed of light to an outside viewer?

[Severian]

But if it did, wouldn't it be going faster then the speed of light to an outside viewer?

 

No - not at all. That is the whole point of special relativity - it alters the transformation connecting the measurements of different observers. The velocities of the train and the bullet no longer just add.

 

If the bullet has speed [math]v_b[/math] in the train's rest frame (the frame the gun is stationary in) and the train travels at speed [math]v_t[/math] relative to the ground, then to someone standing next to the tracks (stationary with respect to the ground) the bullet will appear to go at a speed.

 

[math] \frac{v_b+v_t}{1+v_bv_t/c^2}[/math]

 

You can convince yourself that this is always <c.

[aommaster]

Severian: Is that the equation for special relativity? I'm also guessing that general relativity has nothing to do with it?

[Severian]

Yes, that is the equation for the addition of velocities in special relativity. You would only need general relativity if the train (or the bullet) was accelerating.

[aommaster]

And taking a look at the equation you wrote...

as the two velocities get higher, the bullet seems to travel at a speed towards infinite?

 

I'm taking a look at the denominator.

[math]

1-v_bv_t/c^2

[/math]

if the vb and the vt get towards the speed of light, the denominator tends towards 0. What does this mean?

[swansont]

Dont Star Trek or Star Wars or something have something to do with hyperspace travel. Got no idea what hyperspace even is, all I know is stars move by unrealistically fast and they never run into them.

 

Those are both science fiction. The writers of those shows were free to make up anything they want, and exercised that right liberally at times.

[Severian]

And taking a look at the equation you wrote...

as the two velocities get higher' date=' the bullet seems to travel at a speed towards infinite?

 

I'm taking a look at the denominator.

[math']

1-v_bv_t/c^2

[/math]

if the vb and the vt get towards the speed of light, the denominator tends towards 0. What does this mean?

 

Sorry - I had a typo. I got the sign wrong in the denominator. It should be correct now.

[aommaster]

Ok. Now that makes alot of sense!

 

Thanks for that!

[GrandMasterK]

Ok, other then wormholes, has any other concept been introduced towards getting around in the universe?

 

Do you guys think we'll ever get out of this galaxy, ever???

[oppie]

Another quick question, do we have a measurement for the force of gravity? I was just curious how much force it takes for a black hole to suck in light and about how fast it sucks things in. For instance, humans get pulled down to earth at like 130MPH or so? how fast would I get pulled into a black hole?

 

There is no constant speed in which bodies fall to earth (unless acted upon an external force for example:wind resistance), however there is a constant acceleration(~9.81m/s/s) of falling bodies(in a frictionless environment )on earth.

[TimbaLanD]

There is no constant speed in which bodies fall to earth (unless acted upon an external force for example:wind resistance), however there is a constant acceleration(~9.81m/s/s) of falling bodies(in a frictionless environment )on earth.

 

What happens if you constantly accelerate forever? Can you reach toward the speed of light?

 

Can someone please explain the equation with an example please?

[gagsrcool]

Hi,

 

Yes you can reach the speed of light but relativity forbids you from going much more further.

 

gagsrcool

[danny8522003]

E = mc^2/sqrt(1 - v^2/c^2) shows that when v=c the equation has a 0 as the denominator, any fraction with a 0 at the bottom and a number >0 at the top equals infinity. This is why infinite energy is required to speed objects with rest mass up to c and is therefore impossible. If m = 0 we get a 0 at the top.

As posted in the "mass" thread.

 

Basically, anything with mass cannot b accelerated to the speed of light in a vacuum. Things like quarks can be accelerated to about 99.9% the speed of light but cannot reach it. Only particles with 0 rest mass can reach c.

[Edtharan]

Dont Star Trek or Star Wars or something have something to do with hyperspace travel. Got no idea what hyperspace even is, all I know is stars move by unrealistically fast and they never run into them.

In starwars and star trek (in fact all sci-fi) the space ships move at exactly the speed of "story". Sci-Fi, although it uses a lot of terms that are (or sound like) scientific usualy have nothing to do with the real world. Remember the specific thing avout science fiction is that it is fiction.

 

Ok, other then wormholes, has any other concept been introduced towards getting around in the universe?

 

Do you guys think we'll ever get out of this galaxy, ever???

Wormholes (another staple of Sci-Fi) are curently purely theoretical. They have never been observed, neither has any effect caused by them been observed. They only exist as a mathamatical construct using relativity.

 

If you are looking at pure speculation about what could allow us to travel between the stars then you should look at "Space Drives" (engines that don't use a propelent but "push" against empty space) or "Warp Drives" (not the star trek type).

 

The theoretical Warp Drive works by compressing space in front of it (like a large mass would do) and expanding space behind it (the opposite of what gravity does). There has been no observation of this reverse gravity effect that would be needed for the warp drive to exits (although if we did find some then we could probably make a warp drive).

 

Various ideas for space drives exist, but none have been demonstrated to work. One concept for a space drive works on what is known as the dynamic Casimir effect. This occures when a reflective plate (usually metal) is vibrated back and forth in a particular fashion (this is important and difficult to do). As the plate move back and forth, virtual particles at the surface of the plate are given energy which promotes them into real particles with a velocity away from the plate. The result of this is to give the plate (and anything connected to it) a net velocity in the oposite direction.

 

This kind of space drive could be made today. However, the actual thrust from this drive is extremely small and that makes it impractical as an engine. Also this engine is still theoretical and has only been designed mathamaticaly and not tested in actuality (though the scientists do say the engine could be made more efficent).

 

Currently the best method we have (that we know would work) is to use an Ion Drive space ship, which accelerates for thousands and thousands of years. You would use an Ion Drive in preferance to a standard rocket engine because an ion drive, although it has less thrust, is far more fule efficient that a rocket engine.

[mrblond5311]

What "force" makes space a vacuum? I was told it's " just the lack of air" but that doesn't make sense. Wouldn't there have a be a postive or negative force?