# Am I moving

## Main Question or Discussion Point

Referring to fig 2

Points A,B,E and F are all within a shipping container (Container 1) and the points are at rest wrt the shipping container.

There is a laser at A that fires a thin beam of photons (say a single photon) to point B where there is a very thin detector.

There is an observer at point E and a red light at point F.

If the photons are not hitting the detector then the red light at F turns on.

Still referring to fig 2 there is a second shipping container identical to the container 1, call this container Container 2.

Again points A hat, B hat, E hat and F hat are all within the second shipping container and are at rest wrt that shipping container.

Again there is a laser at A hat that fires an extremely thin beam of photons, a single photon stream, to point B hat where there is a very thin detector.

There is an observer at point E hat and a red light at point F hat.

If the photons from A hat are not hitting the detector at B hat then the red light at F hat turns on.

The observer at E can see the light in Container 2 and visa versa.

Initially the 2 sea containers are at rest wrt each other and the lasers are aligned so that the photons in each container strike point B and B hat respectively.

Container 1 is then accelerated up to a constant velocity D. At all times the observer in container 1 can see the light in container 2 and visa versa

Referring to fig 3
This is a magnified view of container 1 which is now moving at a constant velocity. As can be seen the photons in container 1 will take a finite time to travel from point A to the opposite side of the container. In that time the as container 1 is moving at some velocity D the container would have moved to a new position in space by the time the photons strike the opposite side of the container. Therefore the photons will NOT strike point B but will instead strike some other point to the left or right of B. Ill assume they strike a point to the left of B, point G.

As the photons are not striking point B the light at F will turn on and the observers at points E and E hat will see that light.

The observer at E will know he is moving as the light has come on.

The observer at E hat will know the observer at E is moving wrt E hat as E hat will see the light.

As the light at F hat has not turned on the observer at E hat and E will know he (the observer at E hat) is not moving.

Anyone disagree ?

Referring to fig 4
The observer at E in container 1 now knows he is moving he doesn’t know his velocity or direction.

I now want to propose a method of determining direction and relative velocity

In fig 4 I have a third container that is identical to the other two containers (container 3). This container is set up identical to the other 2 containers.

Whilst container 3 is at rest wrt containers 1 and 2 the laser in container 3 is adjusted so the photons move from point A in container 3 and strike point B in container 3. Which is the same as described above.

Again in container 3, there is a laser at point A that fires a thin beam of photons or say a single photon stream at point B in container 3. There is an observer at point E and a light at point F in container 3.

Fig 4 is identical in every way to figs 2 and fig 3. The only difference is that the apparatus in fig 4 can be rotated in the direction of the circular arrow in fig 4.

Assume the light at point F in container 3 has come on so the observer in container 3 knows he is moving but doesn’t know the direction or velocity. Suppose the direction of movement is in the direction of the arrow shown at point V in container 3.

By rotating the apparatus and measuring the length of deflection of the photons from point B, when this length is at its greatest, the observer in container 3 can determine the direction of travel.

By measuring the length of deflection the observer in container 3 can determine his relative velocity but not his absolute velocity. The observer in container 3 will know his velocity relative to the velocity of the container where the light has NOT come on. If relative velocity is known time dilation is known and length contraction is known relative to the container where the light has NOT come on.

Anyone disagree ?

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JesseM
The laser beam will always move parallel to the orientation of the laser apparatus in the laser apparatus' rest frame. So, it will always hit the same point on the wall of the shipping container--in a frame where the shipping container is moving, the laser beam will appear to slant so that photons remain directly above the laser apparatus even as the laser apparatus moves sideways.

I believe the container will distort in shape (length contraction and curvature at the top as viewed from the side) due to its velocity.

In the moving container (Container 1) if the photons are moving from one side of the container to the other side. From the perspective of observer E, the observer in (container 1), will the photons hit point B or point G?

If Point B why ?

In the moving container (Container 1) if the photons are moving from the floor to the ceiling, ie the laser is mounted in the floor. From the perspective of observer E, the observer in (container 1), will the photons hit point B or point G?

If Point B why ?

if I am driving along in a car and I fire a machine gun out the window perpendicular to the direction of travel of the car and I watch the bullets will the bullets form a line at an angel to the car moving backwrds from the car, similar to the wake at the front or back of a boat?

Now if I am driving in a car and I shine a laser out the window perpendicular to the travel of the car and i can see the photons shooting off into space will the photons form a line at an angel moving back behind the car the same as the bullets in scenario 1 ?

JesseM
I believe the container will distort in shape (length contraction and curvature at the top as viewed from the side) due to its velocity.

In the moving container (Container 1) if the photons are moving from one side of the container to the other side. From the perspective of observer E, the observer in (container 1), will the photons hit point B or point G?

If Point B why ?

In the moving container (Container 1) if the photons are moving from the floor to the ceiling, ie the laser is mounted in the floor. From the perspective of observer E, the observer in (container 1), will the photons hit point B or point G?

If Point B why ?
I don't understand what's different about these two paragraphs. In any case, if the laser apparatus is pointed at point B, the photons will always strike point B regardless of the container's (inertial) motion. I don't know what to tell you about the "why" question, it's just a feature of the laws of electromagnetism that a directed beam from some apparatus, like a laser or a flashlight, always moves in the same direction in the apparatus' rest frame, and therefore must appear slanted in the frame of an observer who sees the apparatus in motion. The laws of electromagnetism are after all Lorentz-symmetric, which means you can mathematically prove that they must work the same in all the inertial frames related by the Lorentz transformation. All the other known laws of fundamental physics are Lorentz-symmetric too, so your quest to try to find a way to detect absolute motion is destined to fail, unless you discover some new laws of physics which aren't Lorentz-symmetric.

JesseM
if I am driving along in a car and I fire a machine gun out the window perpendicular to the direction of travel of the car and I watch the bullets will the bullets form a line at an angel to the car moving backwrds from the car, similar to the wake at the front or back of a boat?
In whose frame? In the car's rest frame the bullet's will fire straight out, just like if the car was at rest relative to the ground. And in any frame where the car is moving, the bullets have exactly the same forward momentum as the car, so naturally they don't go behind or ahead of the car as long as it continues to move inertially.
rab99 said:
Now if I am driving in a car and I shine a laser out the window perpendicular to the travel of the car and i can see the photons shooting off into space will the photons form a line at an angel moving back behind the car the same as the bullets in scenario 1 ?
The laser behaves just like the bullets, with the photons not falling behind the car in the frame where the car is moving, and the laser going straight out in the car's rest frame.

The laser behaves just like the bullets, with the photons not falling behind the car in the frame where the car is moving, and the laser going straight out in the car's rest frame.
No I actually think you are wrong here.

The reason the bullets move with the car is the velocity of the car is imparted to the bullet as a bullet is ballistic in nature.

The velocity of the car is NOT imparted to a photon as a photon is NOT ballistic. The photon moving with the car must be some other phenomenon other than a ballistic phenomenon.

JesseM
No I actually think you are wrong here.

The reason the bullets move with the car is the velocity of the car is imparted to the bullet as a bullet is ballistic in nature.

The velocity of the car is NOT imparted to a photon as a photon is NOT ballistic. The photon moving with the car must be some other phenomenon other than a ballistic phenomenon.
I didn't say the velocity of the car is imparted to the photons, but the velocity of the car does affect their direction. Again, this is just what is predicted by the laws of electromagnetism, and we can easily see it must work this way given the fact that these laws are provably Lorentz-symmetric.

sorry you are not wrong but the phenomenon acting on the photons is diferent to the phenomenon acting on the bullets :)

Dale
Mentor
sorry you are not wrong but the phenomenon acting on the photons is diferent to the phenomenon acting on the bullets :)
The bullets travel in a straight line due to inertia. The laser travels in a straight line due to Maxwell. They both travel in a straight line.

The direction/angle of a straight line of travel is trivially frame-variant.

The laser beam will always move parallel to the orientation of the laser apparatus in the laser apparatus' rest frame. So, it will always hit the same point on the wall of the shipping container--in a frame where the shipping container is moving, the laser beam will appear to slant so that photons remain directly above the laser apparatus even as the laser apparatus moves sideways.
Photons in a staionary frame dont slant photons in a moving frame slant measure the angel if it isnt 90 degrees then Im moving ?

Doc Al
Mentor
Photons in a staionary frame dont slant photons in a moving frame slant measure the angel if it isnt 90 degrees then Im moving ?
You're not moving with respect to yourself. As has been pointed out several times, you will not detect any slanting in your own frame. Someone else can measure the degree of slant and use that as a measure of your speed with respect to their frame.

say i have a square laser and the photons exit perpendicular to the ends of the laser.

In the moving frame are the photons exiting perpendicular to the ends of the laser ? I assume they must be or the person at rest wrt the frame would measure an angel.

If no angel can be measured then the entire laser must have rotated yeh?

Now referring back to my drawings if at rest the end of the laser is exactly flush and flat with the side of the container and then the sea conatiner moves at a constant velocity then the side of the conatiner will be flat except where the rotated laser is located yes?

Doc Al
Mentor
say i have a square laser and the photons exit perpendicular to the ends of the laser.
Perpendicular according to you.

In the moving frame are the photons exiting perpendicular to the ends of the laser ?
No.
I assume they must be or the person at rest wrt the frame would measure an angel.
No.

If no angel can be measured then the entire laser must have rotated yeh?
No.

Dale
Mentor
I assume they must be or the person at rest wrt the frame would measure an angel.

If no angel can be measured then the entire laser must have rotated yeh?
I believe you meant "angle", a unit for measuring arcs, instead of "angel", a divine messenger. Although, given the quasi-religious nature of your posts here and elsewhere, perhaps you wrote what you meant.

PS I know I really shouldn't harass people about spelling mistakes, but I thought it amusingly ironic

Last edited:
russ_watters
Mentor