Contraction effects at relativistic velocities

[bino]

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B would shoot first right?

 

[zefram_c]

What are you talking about " the real math"??

I apologize for a poor choice of words, I simply referred to this statement:

You are assured that at least one will get a near miss at the nose & the cannon behind to miss by -- I'll do the real math on that later.

I was thrown off track by all the references to who beat who, but the follow-up was much clearer.

For the observer to see simultaneous firings, The planet must fire B before A and every cannon out to the end must be advanced by an additional 184.8 nsec... the Ships would see the cannons making their hits on 184.8 intervals also, BUT in the opposite order with the first Ship being hit first.

This is incorrect. De-synchronization is a frame-dependent effect, but not in the manner you derive. Since the observer is moving in the same direction as the ship, the order of the firing will be the same for him and the moving ship. In fact the moving ship will measure a larger delay. For an observer to see the same offset of 184.8ns but in the opposite direction, he would have to move at a velocity opposite to the first observer (ie. if the first observer travels at 0.63c towards the planet so he sees the planet approach him in front and the ships from behind at .63c each, the other observer would be moving at .63c away from the planet with a .9c velocity relative to the first one, and a greater velocity relative to the ships.)

So yes all three views are seeing something different: first to last; last to first; or all at the same time.

This is indeed true. Since the firings of the cannons are events with a spacelike separation (they are simultaneous and spaced out in the planet frame), there always exists one frame in which they are simultaneous, and two frames in which either occurs first. This is a property of all spacelike separated events.

But now reality of what happens, all ships are hit and which two of the 102 cannons miss, still matches with all views.

Agreed. If you time the bullets such that the ships are hit, all frames will agree which bullet hit what. Edit: This thread discussed different situations, so I make no claim that any particular situation will result in a hit.

I'd expect the speeds of .63c plus .63c to give the ships a total speed of 1.26c resulting in "Sonic Light Booms" so bizarre I wouldn't know how to describe them!

Sounds like someone's forgetting relativistic addition of velocities again

 

[RandallB]

For an observer to see the same offset of 184.8ns but in the opposite direction, he would have to move at a velocity opposite to the first observer (ie. if the first observer travels at 0.63c towards the planet so he sees the planet approach him in front and the ships from behind at .63c each, the other observer would be moving at .63c away from the planet with a .9c velocity relative to the first one, and a greater velocity relative to the ships.)

Didn't said the observer would see and offset. I said "For the observer to see simultaneous firings, The planet must fire B before A "
simultaneous OK
And I have no idea where your second 'observer' is.
We have a planet, one observer, and the ships.

Sounds like someone's forgetting relativistic addition of velocities again

Sounds like someone diden't read the question.
SO you think you can give an answer to post #47 ??
You tell me without lorenz contraction how are you going to keep "relativistic addition of velocities" ?

Randall B

 

[RandallB]

randallb your still not making sense. that does not anwser my questions. nothing is moving so that it would be moving faster then c if there were no lorenz contraction.

Of course things would move faster than c if you DUMP contraction!
Without contraction you can not just assume "relativistic addition of velocities" it comes from the fact that contraction exists.

RB

 

[Doc Al]

I'd expect the speeds of .63c plus .63c to give the ships a total speed of 1.26c resulting in "Sonic Light Booms" so bizarre I wouldn't know how to describe them!

Sounds like someone's forgetting relativistic addition of velocities again

I believe RandallB was giving an answer for the case without Lorentz contraction. Of course, in such a case the velocities of 0.63c would never arise. (0.63c came up because RandallB wanted an observer who sees both ship and planet moving at the same speed. Without relativity, that speed would just be 0.45c with respect to the planet. Of course, without relativity there is no reason to introduce a third observer.)

 

[RandallB]

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B would shoot first right?

No - not unless you turn the ships around and send them toward the planet!

Try this:

Ships <<<< ...1. 2. 3. 4. 5. 6
Observer <<
Planet - - ...A...B...C...D...E
(B2) occurs before (A1)

Ships << ....1..2..3..4..5
Observer - -
Planet >> ...A..B..C..D..E
(A1) & B2) same time

Ships - - .....1...2...3...4...5
Observer >>
Planet >>>> ......A.B.C.D.E
(B2) occurs after (A1)

So you B needs to fire before A to score the hits
Observer sees simultaneous hits
Ships see A firing before B

Timing and spacing of Cannon on the planet view must both be changed to achieve simultaneous firings and hits from the view of the ships.

Randall B

 

[bino]

ok let's say there is a ship 100ft long moving at .90c. a planet perpendicular has guns 101ft apart at rest. the guns line of fire are parrallel to each other. the planet plans it out so that the ship will be in between the bullets when the ship flies past the planet. would the bullets hit the ship or not?

this was my original question. there is only one ship with a length of 100 when its going .90c. there is two guns separated from each other by 101.A and B are guns they shoot one bullet each the lines are the paths the ship and the bullets go. so it looks like this:
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now my questions are:
would A or B shoot first?
if we set a ship off from the planet instead of guns then the ship we just launched would look like it took off crooked?
what would happen from both views if we did not have the lorenz contraction?

 

[RandallB]

I'm done here

Asprin got it started into a lot of varied questions and ideas here.

Seems like it's gone full circle. I've learned a bit!
Using a half relative speed observer was a good insite I'll use again.

See you in another thread.

RB

 

[bino]

would A or B shoot first?
if we set a ship off from the planet instead of guns then the ship we just launched would look like it took off crooked?
what would happen from both views if we did not have the lorenz contraction?

 

[Doc Al]

If you are serious about getting those questions answered you need to state them precisely. Define each scenario completely.

 

[bino]

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would gun A or gun B shoot first if they shot off at the same time according to the planet?
i know one of them shoots before the other. in which case, instead of shooting off two guns, the planet launches a ship. i assume since both sides of the ship are being launched at the same time one side of the ship would take off before the other from the view of ship A.

 

[Doc Al]

would gun A or gun B shoot first if they shot off at the same time according to the planet?
i know one of them shoots before the other.

According to who? See post #49. (The ship will say gun B fires first.)

in which case, instead of shooting off two guns, the planet launches a ship. i assume since both sides of the ship are being launched at the same time one side of the ship would take off before the other from the view of ship A.

I assume you mean that a large ship taking off vertically with thrusters at each end firing simultaneously according to the planet? Then, correct, the moving ship will observe the front thruster to fire before the back one. There are no "rigid" bodies in relativity.

 

[bino]

i was asking as if there were a ship that had one engine where gun A is and one engine where gun B is. both engines would be launching at the same time according to the planet. and since gun B fires before gun A then engine B would launch before engine A according to ship A. in which case the ship B would be taking off crooked according to ship A. right?

 

[bino]

i was asking as if there were a ship that had one engine where gun A is and one engine where gun B is. both engines would be launching at the same time according to the planet. and since gun B fires before gun A then engine B would launch before engine A according to ship A. in which case the ship B would be taking off crooked according to ship A. right?