Sorry rear door closed and then opened...typo. D On Wednesday, January 22, 2025 at 9:30:29 AM UTC-8 Dirk Van Niekerk wrote:
> Forgive me if this was already done but I would like to clarify the > experiment. Let's assume a covered bridge with two sliding doors. The > bridge is 10 m in length. There is also a car 12 m in length. The front > sliding door is closed and the car drives onto the bridge until the front > almost touches the door and stops. The driver of the car and the bridge > operator both agree that the back of the car sticks out 2 m at the rear. > They propose an experiment. The driver will drive through the bridge at > near the speed of light. When the front of the car is almost at the front > door the bridge operator will quickly close and then open the front door. > And when the back the car is just inside the bridge he will do the same > with the rear door. They complete the experiment and compare notes. > > The bridge guy says that when he was about to close the front door he > noticed that the rear of the car has already passed the rear door, so he > opened and closed both doors at the same time. The driver disagrees. He > sped up to the front door and saw it close and then open. He noticed in his > rear view mirror that that back door was still open and the car still > outside the bridge. As he sped through the front door (now open again) he > notice the rear of the car moving past the rear gate, which then opened and > closed behind him. To resolve the APPARENT paradox they have to account for > length contraction and time dilation. The doors opened and closed > simultaneously in the garage operator's frame but not the driver's > > Dirk > > On Monday, January 13, 2025 at 12:10:04 PM UTC-8 Brent Meeker wrote: > >> >> >> >> On 1/12/2025 11:01 PM, Alan Grayson wrote: >> >> >> >> On Sunday, January 12, 2025 at 6:53:35 PM UTC-7 Brent Meeker wrote: >> >> That's a rather different paradox and of course the answer is nothing >> would happen to the object. The mass increase and length contraction are >> only *relative*: as measured by the observer the object is moving >> relative to. >> >> Brent >> >> It's often stated that the transformed event, usually denoted as the >> Primed Frame, is what is actually measured in the primed frame, such as the >> E and B fields in E&M. But here is an example something NOT measured in >> the primed frame, another is length. So it's hard to consistently interpret >> what the LT does. AG >> >> >> Motion is only relative. The same object at the same time has different >> velocity relative to many other objects. It can't collapse into black hole >> relative to one and not another. In it's own reference frame it must be >> unaffected by inertial motion. In 2 dimensions here's the Lorentz >> transformation of points I used in the garage/car paradox: >> >> (defun lorentz-2d (v) >> "Returns a function that takes a point (t,x) and >> returns the transformed point (t',x')" >> (lambda (p) >> (let ((t0 (car p)) >> (x0 (cadr p)) >> (g (gama v))) >> (list (* g (+ t0 (* v x0))) ;; this is v*x0/c^2 where c=1 >> (* g (+ x0 (* v t0))))))) >> >> >> Brent >> > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/8f81208e-37c5-42da-b70c-508910cb8b9dn%40googlegroups.com.
