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View Full Version : Physics Paradox... Try to solve.

wobblywindow
12-31-2011, 01:18 AM
If I sit on a train moving at the speed of light, and I fire a gun in the same direction as the direction the train is moving in, what happens to the bullet? Keep in mind:
a. Every action has an equal and opposite reaction.
b. An object cannot move faster than the speed of light.

LurkBrah
12-31-2011, 01:25 AM
strong 1rd psot to boggle my mind

Cheezerman
12-31-2011, 01:26 AM
only light has the ability to travel at light speeds because the actual train is an object in itself, thus according to the rule described in "b", this environment/context is entirely fictional and such a thing would never happen. I'd say the bullet travels normally because in this science fiction universe you created, for some reason, the train, the gun, and yourself are not distorted by the sheer ability of traveling at those speeds.

12-31-2011, 01:26 AM
If I sit on a train moving at the speed of light, and I fire a gun in the same direction as the direction the train is moving in, what happens to the bullet? Keep in mind:
a. Every action has an equal and opposite reaction.
b. An object cannot move faster than the speed of light.

1) A train cant move at the speed of light only very close to it.
2) As an observer on the train the bullet will seem like it's traveling at the normal velocity of the bullet. As an observer outside of the train the the bullet will begin to slow in time to a near stand still as it draws nearer to the speed of light. This occurs in order to conserve the absoluteness of the speed of light.

Angra_Mainyu
12-31-2011, 01:28 AM
assuming a gun could function (exist) at the speed of light

I believe the bullet would travel forward for a small amount of time and distance (the bullet would fire forwards but almost instantly the back of the chamber would ram back into it since that itself is traveling in the same direction at the speed of light

my post is also assuming the gun in this question has the capacity to function while moving this fast

a better question would be if the train was moving at the same speed as the bullet

circusmidget
12-31-2011, 01:28 AM
If I sit on a train moving at the speed of light, and I fire a gun in the same direction as the direction the train is moving in, what happens to the bullet? Keep in mind:
a. Every action has an equal and opposite reaction.
b. An object cannot move faster than the speed of light.

orly?

Anything happening within the system doesn't change the acceleration of the actual system.

12-31-2011, 01:36 AM
assuming a gun could function (exist) at the speed of light

I believe the bullet would travel forward for a small amount of time and distance (the bullet would fire forwards but almost instantly the back of the chamber would ram back into it since that itself is traveling in the same direction at the speed of light

my post is also assuming the gun in this question has the capacity to function while moving this fast

a better question would be if the train was moving at the same speed as the bullet

These questions always have to be answered based on the position of the observer because the answer is different relative to who is observing it. Yes a gun would still function on the train and if you were an observer on the train you would see no difference if the train is going at close to the speed of light or 40 MPH. Relative to the train the bullet is still moving at the same speed.

The difference only come from an external observer who would normally see an additive increase in velocity of the speed of the train and the speed of the bullet. This increase still happens, but time is altered in order to preserve the speed of light.

FuzzeWuzze
12-31-2011, 02:07 AM
These questions always have to be answered based on the position of the observer because the answer is different relative to who is observing it. Yes a gun would still function on the train and if you were an observer on the train you would see no difference if the train is going at close to the speed of light or 40 MPH. Relative to the train the bullet is still moving at the same speed.

The difference only come from an external observer who would normally see an additive increase in velocity of the speed of the train and the speed of the bullet. This increase still happens, but time is altered in order to preserve the speed of light.

I guess it depends on if the train is moving "near" or "at" the speed of light i would think? If nothing can move faster than light and you fired the gun, the bullet would not be capable of moving faster when being fired....

C-Winger
12-31-2011, 02:11 AM
1) A train cant move at the speed of light only very close to it.

It must be a light rail.

And depending on the conditions of this hypothetical situation, wouldn't the bullet not fire? I mean, assuming that you and the gun are moving at c, then as soon as the bullet is fired and independent of the gun... wouldn't it cease to match the speed of the the gun, c?

12-31-2011, 02:13 AM
I guess it depends on if the train is moving "near" or "at" the speed of light i would think? If nothing can move faster than light and you fired the gun, the bullet would not be capable of moving faster when being fired....

No, a train can not move at the speed of light only very close to it. Light is the only thing that can move at the speed of light.

12-31-2011, 02:20 AM
It must be a light rail.

And depending on the conditions of this hypothetical situation, wouldn't the bullet not fire? I mean, assuming that you and the gun are moving at c, then as soon as the bullet is fired and independent of the gun... wouldn't it cease to match the speed of the the gun, c?

Not sure what you're saying. A gun not firing would break the laws of physics as well.

In order for the laws of physics to not be broken it must be an impossibility to travel at the speed of light, only very very close to it. The closer to the speed of light you get, the more difficult it becomes. The closer to the speed of light you get, the slower time moves relative to an outside observer. Time moves slower in order to compensate for the fact that you can't reach the speed of light. Where an observer on the train would see the bullet fire in a fraction of a second and outside observer would see the event take years or longer.

In case you're a non believer, the relativity of time has actually been proven using atomic clocks synchronized on earth and then taking one of the clocks on an airplane trip around the world. The clock which traveled at the higher speed ends up a fraction of a second slower than the one which stayed on earth.

http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

MiKey4
12-31-2011, 02:21 AM
Anything which has no rest mass can travel at the speed of light. Since a train a gun and a bullet all have rest mass this situation could never be achieved.

In short, there is no such thing as an observer who can witness these massive objects travelling at the speed of light.

armyr0b
12-31-2011, 07:09 AM
not boggled at all. you simply forgot the theory of RELATIVITY

its all a matter of relativity. if you are on a hypothetical train moving at light speed and you fire the weapon the people just goes the speed of whatever velocity it should be. same thing as being on planet earth. we are moving at about 67k miles an hour, not including the speed in which the solar system spins within in the outer bands of the milky way. we are going at quite a phenomenal speed relative to the entire universe. that is why when you are in that speed of light train you are not moving the speed of light yourself.

kfx450r
12-31-2011, 08:51 AM
If I sit on a train moving at the speed of light, and I fire a gun in the same direction as the direction the train is moving in, what happens to the bullet? Keep in mind:
a. Every action has an equal and opposite reaction.
b. An object cannot move faster than the speed of light.

Cool story bro. Same speed...neither is faster so its still traveling at the speed of light just moving at the same speed as you so technically you should see it flying next to the train

NeoginCF
12-31-2011, 09:25 AM
If I sit on a train moving at the speed of light, and I fire a gun in the same direction as the direction the train is moving in, what happens to the bullet? Keep in mind:
a. Every action has an equal and opposite reaction.
b. An object cannot move faster than the speed of light.

ITT OP does not realise the physics we experience in everyday life doesn't apply to high velocity's.

newton's laws are an exceptional case of einstein's laws.

Ecooke21
12-31-2011, 09:51 AM
i plane is on a conveyor belt....... will it fly?

dixie_normus
12-31-2011, 10:18 AM
the bullet will be fired as it normally would be.
this is like saying if u jump while on an airplane, you will move back a seat or two. (which is not the case)
relativity brah

12-31-2011, 11:24 AM
ITT everyone claims relativity, but doesn't actually answer the OPs question.

Nara62629
12-31-2011, 12:16 PM
yeah so i guess a paradox is when u create a problem using something impossible and then constraining it with something true...

Wolf-Baron
12-31-2011, 06:28 PM
If I sit on a train moving at the speed of light, and I fire a gun in the same direction as the direction the train is moving in, what happens to the bullet? Keep in mind:
a. Every action has an equal and opposite reaction.
b. An object cannot move faster than the speed of light.

I will answer this based on the bold part of your question.

To get one thing clear here, when you have motion you NEED to include relativity.
for ex;
-You're on a train moving at 80mph and there's a bystander watching, relative to the bystander you will be moving 80mph.
-But relative to the train, you wouldn't be moving.

Another example a little bit close to home here:
-You're on a train moving at 80mph and shot a bullet (let's say the speed of the bullet is 766mph for this example), to the bystander he or she will measure the speed of the bullet and the train altogether (which will be 80mph + 766mph = 846mph).
-Relative to you, you would only measure the bullet speed (766mph)

Okay now there's an additional part to this question here, does the bullet pierce through the train? If so how fast does it go? We can break this down as well..
If your on a train moving at 99% of the speed of light and you shot a gun and the bullet itself pierced through the train, it would move faster than the speed of light right? I mean using the velocity adding technique you would think that since you're already moving at the speed of light and you add the velocity of the bullet itself, it would be moving faster than light.
Wrong, one thing to remember is that the velocity adding method doesn't apply when dealing with things near light speed. Light will always be faster than the object, the reason being is dilation and length contraction.

You can research "Dilation and length contraction" if you don't know what that is.

AboveAverage
12-31-2011, 06:31 PM
The train would actually slow down a little bit when the gun is fired. The bullet may be traveling near the speed of light, but the train is traveling slower.

sorta answered your own question OP, a. Every action has an equal and opposite reaction.

ch00se
12-31-2011, 06:39 PM
ITT : this misc does the OPs homework

12-31-2011, 06:40 PM
Okay now there's an additional part to this question here, does the bullet pierce through the train?

Whether or not the bullet pierces the train is irrelevant. If you fire the bullet inside the train or lean outside the window and fire the bullet the scenario is exactly the same (assuming no air resistance).

Wolf-Baron
12-31-2011, 06:43 PM
Whether or not the bullet pierces the train is irrelevant. If you fire the bullet inside the train or lean outside the window and fire the bullet the scenario is exactly the same.

exactly, that's why I didn't understand OP's question when he says "What happens to the bullet"
He probably expects it to go through a wormhole or some sheit lol

12-31-2011, 06:46 PM
exactly, that's why I didn't understand OP's question when he says "What happens to the bullet"
He probably expects it to go through a wormhole or some sheit lol

And I think the velocity adding method still does work near the speed of light it's just that time and distance compress in order to change the velocity such that the speed of light is not exceeded.

MiscMathematician
12-31-2011, 06:50 PM

Assuming an observer is on an object moving at 1m/s less the speed of light and fires a laser in the direction of his movement, what would happen. Well, to the observer on the object, the laser beam would fire at the speed of light away from him. An outside observer would see the beam of light moving away from the observer at 1m/s.

12-31-2011, 06:52 PM

Assuming an observer is on an object moving at 1m/s less the speed of light and fires a laser in the direction of his movement, what would happen. Well, to the observer on the object, the laser beam would fire at the speed of light away from him. An outside observer would see the beam of light moving away from the observer at 1m/s.

I don't want to live on this planet anymore.

MiscMathematician
12-31-2011, 07:15 PM
Try these (I'm actually not sure of the answers):

1) Assuming the above scenario, what does an outside observer see if the person on the object fires a laser in the direction opposite his movement?

2) Now assume two objects travel away from one another in opposite directions at exactly 0.5C. Can observers on the objects see each other? (Take note that light must reflect off of one observer and reach the other for this to happen).

DanielHimself
12-31-2011, 08:22 PM

Assuming an observer is on an object moving at 1m/s less the speed of light and fires a laser in the direction of his movement, what would happen. Well, to the observer on the object, the laser beam would fire at the speed of light away from him. An outside observer would see the beam of light moving away from the observer at 1m/s.
Your physics professor gave you that answer? The speed of light has the same value in every direction in all inertial frames (which includes the outside observer's frame). Both the observer on the object and the outside observer would observe the beam of light (the laser) moving at c. The speed of light is invariant under the Lorentz transformation.

EDIT: forgot about your post above. If fired in the opposite direction, both observers still observe the laser travelling at speed c. Not sure about the second one. Since they're inertial frames, the first observer can be considered motionless and the second observer considered to be travelling away from him at speed <c.

MiscMathematician
12-31-2011, 08:32 PM
Your physics professor gave you that answer? The speed of light has the same value in every direction in all inertial frames (which includes the outside observer's frame). Both the observer on the object and the outside observer would observe the beam of light (the laser) moving at c. The speed of light is invariant under the Lorentz transformation.

That sentence was weird, replace the second observer with "observer on the object"

PaulG
12-31-2011, 08:35 PM
Bullet would destabilize into raw particles just like the train would.

DanielHimself
12-31-2011, 08:37 PM
That sentence was weird, replace the second observer with "observer on the object"
Okay, that makes a little more sense. Still, both the observer on the object (firing the laser) and the ground observer will observe the laser travelling at c.

MiscMathematician
12-31-2011, 08:47 PM
Okay, that makes a little more sense. Still, both the observer on the object (firing the laser) and the ground observer will observe the laser travelling at c.

Yes, exactly. Relative to the observer, the object is moving at C-1m/s, the light beam would be travelling at C.

DanielHimself
12-31-2011, 08:53 PM
Yes, exactly. Relative to the observer, the object is moving at C-1m/s, the light beam would be travelling at C.
Yes, exactly. I don't know if we are disagreeing or agreeing on this lol

MiscMathematician
12-31-2011, 09:13 PM
Yes, exactly. I don't know if we are disagreeing or agreeing on this lol

Agreeing! Have an idea about the other questions I posed?

DanielHimself
12-31-2011, 09:17 PM
Agreeing! Have an idea about the other questions I posed?

I edited my first post (#29).

wobblywindow
01-01-2012, 04:48 AM
orly?

Anything happening within the system doesn't change the acceleration of the actual system.

I completely agree, but isn't the gun and bullet already travelling at that speed before being fired (as it is inside the train moving at the speed of light)?

wobblywindow
01-01-2012, 04:55 AM
I will answer this based on the bold part of your question.

To get one thing clear here, when you have motion you NEED to include relativity.
for ex;
-You're on a train moving at 80mph and there's a bystander watching, relative to the bystander you will be moving 80mph.
-But relative to the train, you wouldn't be moving.

Another example a little bit close to home here:
-You're on a train moving at 80mph and shot a bullet (let's say the speed of the bullet is 766mph for this example), to the bystander he or she will measure the speed of the bullet and the train altogether (which will be 80mph + 766mph = 846mph).
-Relative to you, you would only measure the bullet speed (766mph)

Okay now there's an additional part to this question here, does the bullet pierce through the train? If so how fast does it go? We can break this down as well..
If your on a train moving at 99% of the speed of light and you shot a gun and the bullet itself pierced through the train, it would move faster than the speed of light right? I mean using the velocity adding technique you would think that since you're already moving at the speed of light and you add the velocity of the bullet itself, it would be moving faster than light.
Wrong, one thing to remember is that the velocity adding method doesn't apply when dealing with things near light speed. Light will always be faster than the object, the reason being is dilation and length contraction.

You can research "Dilation and length contraction" if you don't know what that is.

wobblywindow
01-01-2012, 04:57 AM
ITT : this misc does the OPs homework

Nah man, this is the one situation we're always talking about in physics instead of learning because the teacher's semi-retarded and doesn't teach.

Tamorlane
01-01-2012, 09:22 AM
This was addressed by Hawking in the documentary Into the Universe. His example is the train moving at 99 percent the speed of light, and what if a girl got up from her seat and ran down the hallway of the train....would she not be now going faster than the speed of light....

He says the speed of light works as a cosmic speed limit and will actually slow the girl down to protect itself. The slowing wouldnt likely be noticeable but it would occur. The universal laws protecting themselves.

3:18

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