Neutrino apparently moving faster than light

[Arwin]

Sorry Arwin, but this is utter bunkum. STR is not some kind of "cheat" - it's been experimentally proven. You seem to be saying that because it's counter-intuitive it must somehow be a mathematical trick.

So I've been reading through that link and also some other related stuff, but I can't find anything. Nothing there is even remotely as counter-intuitive as this. Everything is about the speed at which photons, neutrinos et all travel, what kind of effect gravitational forces has on them (and NPL clocks), etc. All straightforward (relatively ) stuff. Perhaps you guys can't explain what you mean very well, or you are bringing in factors I am not, but you simply cannot imagine not bringing in these factors. I think I'll have to continue reading on my own and see if I can figure out what's going wrong from there on my own, and then report back.

 

[Davros]

Dunno whether you're being sarcy or not, but rpg.314 has already posted a link that explains it. Read it.

You mean this : https://secure.wikimedia.org/wikipedia/en/wiki/Velocity-addition_formula

You really Think that i could understand that



/Davros (who would never refer to himself in the third person btw) has spent much time trying to convince b3d readers of his genius,
must now consider the idea that he has succeeded far to well

 

[sebbbi]

It's just like tonemapping. No matter how many and/or how bright lights you add together, the result is always under 1.0.

 

[Arwin]

It's just like tonemapping. No matter how many and/or how bright lights you add together, the result is always under 1.0.

Nice one

Well I hit the jackpot pretty quick:

http://www.physicsforums.com/showthread.php?t=249903

 

[Davros]

And now for something simpler :
you have an airplane on a massive conveyor belt and as the plane moves forward the belt move backward at the same speed to compensate - Will the plane take off ?

 

[manux]

And now for something simpler :
you have an airplane on a massive conveyor belt and as the plane moves forward the belt move backward at the same speed to compensate - Will the plane take off ?

Ofcourse the plain will take off. The airplane tires are "free to rotate" and all power(push) used to move the plain comes from the engines not from the tires.

 

[cjo]

Ofcourse the plain will take off. The airplane tires are "free to rotate" and all power(push) used to move the plain comes from the engines not from the tires.

But it is the movement of the wings through the air which gives them the lift to take off. The plane won't be moving relative to the air (only relative to the conveyer belt), meaning it doesn't reach the required airspeed to lift off.

Not sure what the plane question has to do with neutrinos or light though - at non-relativistic speeds, velocities add normally.

The velocity of object A as seen from object B is

(v(A) + v(B)) / (1 + ((v(A)*v(B)) / c^2))

If v(x) is close to 0c then the result approaches (v(A) + v(B))/1

If v(x) is close to c, then the result approaches (v(A) + v(B)) / 2

If you assume that the maximum value of v(x) is 1c, then the maximum observed velocity of object B from the viewpoint of object A is 1c.

 

[3dilettante]

The belt has a small effect on the plane's motion because the wheels will rotate faster without imparting enough energy to the plane to push against engine thrust.

The belt would have to be going very fast indeed for the friction that imparts a small amount of the belt's motion to the plane to overcome thrust.

 

[snarfbot]

if i understand correctly this is the point arwin is making.

if 2 hypothetical ftl-trains facing opposite directions were able to magically accelerate to the speed of light instantaneously, travel for precisely 1 second and then stop instantly, would they not end up 599584916 meters away from each other?

because according to that equation, they would be 299792458 meters away from each other, or the speed that light travels in 1 second.

so that equation can only account for the apparent speed from the point of reference of one of those moving objects

 

[cjo]

No, it is to do with relativity. From the point of view of someone standing at the train station, each of the trains was travelling at 1c, which doesn't cause a problem. Time runs "normally" from the perspective of this person.

From the point of view of someone on the train, the other train was travelling away at 1c because the perception of time changes at relativistic speeds - so speed = distance travelled / time taken, but you have to take in to account the fact that time changes at high speed.

 

[snarfbot]

From the point of view of someone on the train, the other train was travelling away at 1c because the perception of time changes at relativistic speeds - so speed = distance travelled / time taken, but you have to take in to account the fact that time changes at high speed.

i think that if you were an occupant of one of the trains it would be impossible to observe the other train or measure its speed because light reflected off the caboose for instance, wouldnt be able to reach you until you stopped.

its interesting to think about tho

 

[cjo]

i think that if you were an occupant of one of the trains it would be impossible to observe the other train or measure its speed because light reflected off the caboose for instance, wouldnt be able to reach you until you stopped.

its interesting to think about tho

Ok, if you take it as both travelling at v(A) = v(B) = 0.999999999999999999999999999999999999999999999999999999999c, then you would be able to detect the other train, but it still wouldn't be travelling at v(A) + v(B) (i.e. almost 2c) from the point of view of someone on the train - it would be moving away at just under 1c.

 

[manux]

But it is the movement of the wings through the air which gives them the lift to take off. The plane won't be moving relative to the air (only relative to the conveyer belt), meaning it doesn't reach the required airspeed to lift off.

I doubt the conveyor belt would move air that much. Planes wings probably are 2-3m high and the amount of air conveyor belt would have to move is quite significant.

Ofcourse if the conveyor belt was really wide and designed to move air instead of efficient operation and it would move super fast then perhaps it would move so much air plain wouldn't be able to take off. On the other hand then turning around the plane it should be able to hover in the air without using it's engines(or using engines minimally)

To be able to keep the plane on the belt the belt needs to be smooth which kind of implies low drag which then... I think the belt in practical terms will not have significant negative impact on the planes capability to take off.

 

[Arwin]

OK I have a visual example that I'd like to offer with a question to follow.

1. Lets say you have a gun that is traveling at the speed of light in the negative direction from + to - on an X axis.
2. At the instant the gun passes the origin "0" it fires a bullet at the speed of light in the positive direction from 0 to + on the X axis.
3. If the bullet were to represent a ray of light, what would an observer standing at point +5 on the X axis see? Would the observer see the gun moving away or standing still? Assume the observer has no frame of reference relative to the gun eg no background or floors etc.
4. What would the observer see if they were moving at the speed of light in the positive direction from +5 to +infinity?

:smile:

3. Gun moving away, as the light moves away in the opposite direction, both at the speed of light. The distance between them is observed to increase at twice the speed of light. The speed of the gun has no influence of the speed of light, so the 'light' bullet moves at the speed of light in the opposite direction, and as both are moving away from each other, the observer has a frame of reference.

4. Nothing. Neither light from the gun nor from the light bullet ever reaches him as he is traveling at the speed of light in a direction parallel to the bullet and opposite of the gun.

if i understand correctly this is the point arwin is making.

if 2 hypothetical ftl-trains facing opposite directions were able to magically accelerate to the speed of light instantaneously, travel for precisely 1 second and then stop instantly, would they not end up 599584916 meters away from each other?

because according to that equation, they would be 299792458 meters away from each other, or the speed that light travels in 1 second.

so that equation can only account for the apparent speed from the point of reference of one of those moving objects

Yep. And yes, turns out I was actually right about the factor that messes with the constant. It's called time - as usual, time changes everything.

 

[cjo]

I doubt the conveyor belt would move air that much. Planes wings probably are 2-3m high and the amount of air conveyor belt would have to move is quite significant.

Ofcourse if the conveyor belt was really wide and designed to move air instead of efficient operation and it would move super fast then perhaps it would move so much air plain wouldn't be able to take off. On the other hand then turning around the plane it should be able to hover in the air without using it's engines(or using engines minimally)

To be able to keep the plane on the belt the belt needs to be smooth which kind of implies low drag which then... I think the belt in practical terms will not have significant negative impact on the planes capability to take off.

Read what I actually said (and read the question).

While the plane is on the ground, the engines provide thust, which causes it to roll forwards against the stationary ground and air. As the plane gets faster, the air over the wings eventually moves fast enough to provide enough lift for the plane to take off.

If the plane is on a moving conveyor belt which moves backwards as the wheels move forwards, the plane will only be moving relative to the conveyor, not the ground (or the air). This means that the air speed over the wings is 0mph, which isn't enough for the wings to provide lift, so the plane cannot take off.

 

[manux]

Read what I actually said (and read the question).

While the plane is on the ground, the engines provide thust, which causes it to roll forwards against the stationary ground and air. As the plane gets faster, the air over the wings eventually moves fast enough to provide enough lift for the plane to take off.

If the plane is on a moving conveyor belt which moves backwards as the wheels move forwards, the plane will only be moving relative to the conveyor, not the ground (or the air). This means that the air speed over the wings is 0mph, which isn't enough for the wings to provide lift, so the plane cannot take off.

The fact that conveyor belt is moving doesn't necessarily imply that the air under wings is moving significantly. It can be true that conveyor belt is moving but air under wings is still stationary(i.e. not affected by conveyor belt) or moving only slightly. This all depends how much drag conveyor belt has and it should be minimal as conveyor belt has to be smooth.

If conveyor belt caused easily such a "wind" it would be perfect for wind tunnels, but it just isn't so. Especially not when you need to move 2-3m tall air mass.

 

[Davros]

but it still wouldn't be travelling at v(A) + v(B) (i.e. almost 2c) from the point of view of someone on the train - it would be moving away at just under 1c.

yes but when the 2 trains stopped (instantaneously) after a second would the distance betwwen them be 1 light second or 2 ?

ps: About the plane it came up in another forum and someone said to me you should ask a physicist, so i did
I'll let everyone think about it for a bit

 

[arjan de lumens]

yes but when the 2 trains stopped (instantaneously) after a second would the distance betwwen them be 1 light second or 2 ?

Time dilation applies here; a second in one observer's frame of reference does not necessarily correspond to one second in another observer's frame of reference. If you, as a stationary observer, watch the two trains run for 1 second, then stop, then observers on either train would observe their own train running for less than 1 second (in fact, exactly 0 seconds if they travel exactly at the speed of light) - and also observe that the other train is running for more than 1 second. All observers would in this case agree that the combined running time for the two trains is 2 seconds, but disagree on how those two seconds were split among the two trains. They would also agree that the distance between the trains after the run is 2 light seconds.

 

[3dilettante]

If the plane is on a moving conveyor belt which moves backwards as the wheels move forwards, the plane will only be moving relative to the conveyor, not the ground (or the air). This means that the air speed over the wings is 0mph, which isn't enough for the wings to provide lift, so the plane cannot take off.

This requires that the belt be going extremely fast in the opposite direction.
Unlike with a car, the driving force is engine thrust that is weakly linked to the ground via friction and rolling resistance in the wheels.
Because of this, the belt must race back far faster than the unimpeded takeoff speed of the plane.

Under somewhat realistic scenarios, the belt could not race back fast enough to provide enough force such that a small fraction of it indirectly fed through the landing gear can equal the plane's direct thrust.

 

[manux]

This requires that the belt be going extremely fast in the opposite direction.
Unlike with a car, the driving force is engine thrust that is weakly linked to the ground via friction and rolling resistance in the wheels.
Because of this, the belt must race back far faster than the unimpeded takeoff speed of the plane.

Under somewhat realistic scenarios, the belt could not race back fast enough to provide enough force such that a small fraction of it indirectly fed through the landing gear can equal the plane's direct thrust.

I think he is trying to make a different point. His argument is that the belt causes air above the belt move fast enough that the plane cannot get lift to fly. What I don't buy is that the belt would cause the air move in such a way. The belt just doesn't have the kind of form and surface that would cause the air move in a way that would affect a plane significantly.