Simultaneity Definition and 298 Threads

Hey! So basically I studied General Relativity for a while and was moving on to Special Relativity and there's one thing in it that I can't seem to understand, simultaneity. So I've seen videos explaining it with a train, an observer in the moving train and an observer outside the train as the...

Hi, I read through einsteins popular book on relativity translated into english around 1922 and subsequently read the original 1905 paper on the electrodynamics of moving bodies. So we have a fixed observer seeing flashes happening at the same time and we have a moving observer seeing one...

Is there any method/model for determining simultaneity of events farther apart than light can ever travel? I'm guessing not. Would it be wrong to say that the non-observable universe exists only in our past (or future)?

I was just wondering. According to Lorentz transformations, if two events are simultaneous in one reference frame, they will generally not be simultaneous in another. The time difference that I get between the two events in the other reference frame is \Delta t^{`} = \gamma\beta\Delta x...

I understand when two observer one at rest wrt Earth and the other in motion wrt earth, two events cannot happen at the same time to both the observer. So, is it, the moment, the observer which was in motion comes to rest wrt earth, would two events now, at once happen at the same time, to both...

Am i right in thinking that relativistic simultaneity explanations tend not to mention the fact that one of the ‘simultaneous’ events may well be red shifted and the other blue shifted and by analysing wavelengths you could presumably work out whether the event was in reality simultanous or not.

I found this spacetime diagram at https://en.wikipedia.org/wiki/Proper_acceleration with an accelerating traveler, resulting in "curved" hyperplanes of simultaneity. Notice how the simultaneity planes are angled "normally" (The faster the steeper the slope and no slope when stationary) but...

Two spaceships with their engines shut off and identical radio receiver-amplifier-reemitting devices are in the empty space, very far from each other and from any celestial body. The lag time from absorbing to reemitting in the device is vary small compared to the return time of the signal (2t)...

An isolated mechanical system can be represented by a point in a high-dimensional configuration space. This point evolves along a line. The variational principle of Jacobi says that, among many imagined trajectories between two points, only the SHORTEST is real and is associated with situations...

Homework Statement I get ##~t_1-t_2=\frac{u}{c^2}(x_1-x_2)## Homework Equations Lorentz transformations: $$x'=\frac{x-ut}{\sqrt{1-u^2/c^2}}$$ $$t'=\frac{t-ux/c^2}{\sqrt{1-u^2/c^2}}$$ The Attempt at a Solution t' are times in the moving system S' and are equal, the times t in the fixed...

Thanks for opening the millionth thread about this. My teacher has been explaining special relativity and I became confused at simultaneity. This is my train of thought, where did I go wrong? Say a sensor is moving at a speed of c-1 m/s to the right. Somewhere to the left of the sensor there's...

I thought of yet another simultaneity paradox that I find even more confusing: We're just in space with spaceships. There's a ship moving past us at some relativistic speed. On the front and back of the ship there are thrusters at the top that can be activated by a pulse of laser light striking...

My question is based around the popular thought experiment regarding Einstein's relativity of simultaneity. That is, the one regarding two lightning strikes and two observers. Observer 1 is stationary relative to the ground, and is located equidistant between lightning strikes A and B. Observer...

I'll start with link describing the phenomenon: https://books.google.com/books?id=WTfnBwAAQBAJ&pg=PA43&lpg=PA43&dq=relativity+twist+rotating+cylinder&source=bl&ots=C2SDJNPF2K&sig=ImFDYGm_0qK7JoDU0ulsxLk3sMU&hl=en&sa=X#v=onepage&q=relativity%20twist%20rotating%20cylinder&f=false Quote: "A...

I know variations of these have probably been asked numerous times before, but I'm having trouble with this specific scenario. Imagine the classic Train Paradox, except instead of lighting strikes we have an observer at the centre of the train shooting laser pulses towards the rear (Event E1)...

Wasn't sure whether to post this in SR or QP here, but chose the latter. Assuming: 1. The results of a quantum measurement are random, and that Alice and Bob (performing simultaneous measurements on widely separated, entangled particles) end up with measurements that are perfectly correlated...

With both their clocks synced at 00:00 (12 AM), spaceships A and B leave Earth in oposite directions, each at 17308257.5 m/sec (.57735027c), So the Lorentz factor of their relative velocity 259627884.49 m/sec (.866025404c) is 2. They travel in opposite directions at this velocity for 2 hours...

I have some issues understanding the following thought experiment: Suppose you are standing still, and two balls are moving towards you from opposite direction. From your own reference frame, Ball A is ##10^5## m away from you, moving towards you from the left with speed ##0.8c##, and Ball B is...

Hi everybody, I'm new on this forum so I apologize in advance if I don't respect some formalities (and sorry for my English). It is known that in the perspective of the stationary observer the events in the back and in the front of the moving spaceship are not simultaneous. If I understand well...

Homework Statement You are standing at x = 9.0 km and your assistant is standing at x = 3.0 km. Lightning bolt 1 strikes at x = 0 and lighting Bolt #2 strikes at x = 12.0 km. You see the flash from Bolt #2 at t = 10 μs and the flash from Bolt #1 at t = 50 μs. According to your assistant, were...

Homework Statement [/B] Homework Equations The rear clock ahead example gives vL/c^2: The Attempt at a Solution I think the solution is the same, because even if there is a time dilation due to u (downward velocity) both clocks would slow down at the same rate and so the time difference...

Hello everyone, sorry if this is a noob question; I'm just starting out with special relativity. I was wondering whether relativity of simultaneity is a direct consequence of our ability to "know" being dependent on sight (light reaching a point). If, for example, we could only judge an event...

Ok, so here's an example from David Morin's book that I seriously don't understand: Two clocks are positioned at the ends of a train of length L (as measured in its own frame). They are synchronized in the train frame. The train travels past you at speed v. It turns out that if you observe the...

Hi everyone, Recently I randomly thought of a thought experiment of something going faster than light, along the lines of a shadow or some other "non-information carrying object". In this case it would be an empty seat. The idea is to take 800 million and one chairs of half a meter breadth...

I am reminded of Shroedinger's Cat that is only "probably alive or dead" because it is connected to a lethal device that kills if and only if a sub-atomic particle travels to a certain position or is emitted at a certain time, which quantum events have only a probability of occurring. I'm an...

I am puzzled over einstein's thought experiment on simultaneity. In this experiment, a man is standing on a train platform. A woman is sitted in the middle of a moving train traveling towards the man. When the train is half past the man, lightning strikes at the same instant at both ends of...

Einstein's relativity of simultaneity & quantum measurement paradox. Suppose a rocket traveling close to the velocity of light which emits a single photon from its midpoint at point A, illustrated below. The rocket is equipped with a single detector drawn in green at the front of the rocket...

I set up a Twin Paradox scenario and accompanying spacetime diagram to help better understand the resolution, but I had a question about the diagram I was hoping someone here could help answer. Please excuse the hastily drawn diagram! (Note: the ' frame corresponds to the outbound trip, the...

Suppose that frame O' moves at speed v = 0.6c relative to frame O. A rod with two balls is attached to its ends is 10 meters long in its rest frame, O'. Length contraction will tell you that in frame O, the rod is 8 meters long. But aren't the two balls at the ends "events"? They are clearly...

Oops, forgot to finish the title, but don't see how I can edit it. Sorry. How does one reconcile the idea that, according to relativity, one cannot talk of simultaneity, yet one can talk of a slice of spacetime to be space where all the points are at the same time? That is my main question...

Let's say you have a planet rigged to explode only if two bowling balls hit respective sensors at the same time. An unfortunate observer, call him Carl, releases two bowling balls at the same time from his reference frame. Meanwhile, Shirley passes by at nearly the speed of light. From Shirley's...

Homework Statement Two rockets are each 1000m long in their rest frames. Rocket A, traveling at 0.800c relative to the earth, is overtaking Rocket B, which is moving in the same direction at 0.600c. (i) According to the crew on B, how long does A take to completely pass? I.e. how long is it...

I recently started studying Special Relativity an my book discusses the following: Say I have synchronized two separated clocks in a reference frame S, if then an observer in another reference frame S' for whom the clocks are moving sees the clocks he would say those clocks are out of...

There's something I don't manage to understand in the union between the relativity of simultaneity and the uncertainty of a quantum system's state. Observer A is in a lab on Earth. Observer B is approaching Earth at half the speed of light. On Earth, we build an experiment that gives a result...

Obviously I have to learn how to start a topic, but I believed that in a scientific forum, what matters is the idea, not the presentation. I'll try harder this time. Since every scientist knows very well the ladder paradox, I believe I won't be wrong, by missing something in the set. --- A...

OK, guys and galls, I'm back I admit that the ladder paradox topic that I started was put quite stupidly, and I wouldn't have the chance to make my point, even if Peter didn't lock it. But... we had quite a long conversation in private with him, I learned quite few things, and I believe I made...

Hi everybody, Glad to be with you, in the most popular physics forums on the Internet. First of all, I'm not a physicist and the problem I hope to get the answer from you, is part of the work I'm writing in another field. To cut it short, I don't quite understand how the relativity of...

I was reading about (The train-and-platform thought experiment) from https://en.wikipedia.org/wiki/Relativity_of_simultaneity and was wondering a couple of things. 1.) Would the observer on the train agree with the stationary observer that event A and B happen at the same place in the stationary...

I am having a bit of trouble with understanding a basic point re the concept of relativity of simultaneity. I get the point of observers seeing events at different times, due to the passage of time of light traveling to them from the event. But I don't understand why this precludes events being...

Hey guys, i am not a science guy by any means so any answer written for the layman would be much appreciated. i may not be understanding this right but here it goes: In einstein's relativity of simultaneity we talk about how events A,B, and C are simultaneous for one observer (lets call him...

In Einstein's train/lightning strike thought experiment, the embankment and train observers disagree on the simultaneity of the events. But let's alter the experiment so that if the strikes are seen to be simultaneous, ( embankment observer ), the combined strikes blow up the entire...

A yes answer can cause conceptual problems. What is your opinion?

Over the years I've watched Science try to deal with the Information Paradox regarding black holes. http://news.sciencemag.org/physics/2015/12/physicists-figure-out-how-retrieve-information-black-hole I've always been curious how we got to the point where we see this as a problem in need of a...

Hello, I am having a bit of trouble understanding this diagram. I can accept the example of the moving train with an observer beside the train and an observer on the train, then two lights emit from both ends of the train when the train pass the observer. But this diagram is a little confusing...

Hello PF. I have no problem with the embankment observer. He sees the flashes as simultaneous being equidistant. Likewise the train observer who sees the flashes as separate given he is closer to one flash. What I don't follow is what is the significance of this? Thanks.

In the train example that supposedly shows the relativity of simultaneity, why, in the frame of the observer on the ground, the "midpoint" of the train in the train's frame is still the midpoint? Does it have anything to do with Lorentz contraction? If so, there might be some circular reasoning...

If a train is moving towards two simultaneous flashes and is equidistant from them, they will be seen to be simultaneous. Meanwhile a stationary footbridge observer watching the same train approach, also sees the flashes as equidistant, therefore simultaneous. Can someone explain how observers...

Hello PF. Prior to the train/embankment thought experiment, Einstein argues that in order to determine if events are simultaneous, an equidistant observer is required. The embankment observer is equidistant, and when the light from the two flashes reaches him he sees them as simultaneous. The...

Hello PF. There are two lightning flashes , and two stationary observers. Observer 1 who is equidistant from the flashes, sees them as simultaneous Observer 2 stands one step to the side of observer 1, and is not equidistant. He sees the flashes as separate, the light having unequal distances...

As I understand, one of the Special Relativity roots is the statement that two events SIMULTANEOUS in one inertial frame are NOT necessarily simultaneous in another inertial frame that is moving against the first one. To illustrate and PROVE this statement Einstein gave his well known example...