# What is Simultaneity: Definition and 297 Discussions

In music, a simultaneity is more than one complete musical texture occurring at the same time, rather than in succession. This first appeared in the music of Charles Ives, and is common in the music of Conlon Nancarrow and others.
In music theory, a pitch simultaneity is more than one pitch or pitch class all of which occur at the same time, or simultaneously: "A set of notes sounded together." Simultaneity is a more specific and more general term than chord: many but not all chords or harmonies are simultaneities, though not all but some simultaneities are chords. For example, arpeggios are chords whose tones are not simultaneous. "The practice of harmony typically involves both simultaneity...and linearity."A simultaneity succession is a series of different groups of pitches or pitch classes, each of which is played at the same time as the other pitches of its group. Thus, a simultaneity succession is a succession of simultaneities.
Similarly, simultaneity succession is a more general term than chord progression or harmonic progression: most chord progressions or harmonic progressions are then simultaneity successions, though not all simultaneity successions are harmonic progressions and not all simultaneities are chords.

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1. ### I Relativity of Simultaneity and Length Contraction

This has probably been discussed/explained many times before so I apologize in advance. Please just direct me to the relevant thread if it has. In Morin, "Special Relativity For the Enthusiastic Beginner", he explains the loss of simultaneity and specifically the "rear clock ahead" effect. If...
2. ### B Help understanding the Relativity of Simultaneity

Hello everyone, So I think maybe what confused me with the symmetry of time dilation was not understanding relativity of simultaneity. After looking into it if you have two clocks P and Q that synchronize when they meet and if ##\gamma## is 2 then from P's reference frame P equaling 10 and Q...
3. ### I Simultaneity and Reality: Construct a thought experiment similar to this one described by Einstein

I want to construct an experiment similar to that described by Einstein in his thought experiment: https://en.wikisource.org/wiki/Relativity:_The_Special_and_General_Theory/Part_I#Section_9_-_The_Relativity_of_Simultaneity How would I design it to ensure the light from the flashes at the back...
4. ### I Is Simultaneity Absolute or Relative in the Theory of Relativity?

When two remote events are observed/measured to be simultaneous in one inertial frame, the same events will not be simultaneous when observed from a second frame in uniform motion relative to the first. Why is this distinction in the kinematics of light not considered an operational distinction...
5. ### B Quantum entanglement and simultaneity

I know very little about quantum physics. I was looking up the definition of quantum entanglement and asked ChatGPT to explain it. Here is an interesting phrase in its answer: "Once the particles are entangled, measurements made on one of the particles will instantaneously affect the state of...
6. ### B The synchronization of clocks and the relativity of motion

In his thought experiment on the relativity of simultaneity, Einstein synchronizes two clocks A and B (at either end of a rod) to the clock C in a stationary frame, while A and B (the rod) is moving relative to C. The equations Einstein finishes with demonstrate how observers moving with A and...
7. ### A Hyperplanes of Simultaneity and BigBang

As a layman in physics, I cannot understand the block universe concept followed by Rietdijk-Putnam-Penrose Argument. Let me clarify my question as follows: Suppose two objects, one stationary and one moving towards the other one at constant relativistic speed, e.g. 05.c and let's also presume...
8. ### I Relativity & Simultaneity Convention: Meaning & Impact

Hi all, I have been figuring out relativity. I was just wondering how meaningful the simultaneity convention is, how meaningful it is for say something a million light years away to be on our plane of simultaneity. I'm guessing not very, we must really wait for light to get to use to have...
9. ### I Train Simulation: Observer A and B Contradiction?

I have not seen this exact configuration discussed. Observer A in middle of train. Observer B at station. Both A and B think the other is moving. Observer A synchronizes two clocks and puts one at each end of train. Lightning strikes both clocks stopping them when A passes B. B says...
10. ### B A question about relativity of simultaneity

Hello. I'm new here and very much afraid of breaking rules. I would gladly post this question in the Homework section, because it's homework, but my question doesn't fit the template, it's a theory question. I hoped to find it in Relativity FAQ's, but it's not there. I can tell you I grasped...
11. ### I Understanding Simultaneity Through Male & Female Clocks Meeting

This is not a homework question, just a scenario I've come up with. Imagine I have a male and a female clock moving towards each other. If they're in sync, one will fit inside the other and they'll continue on their way. If not, they'll collide. (Apologies for the crude drawings.) I place these...
12. ### SH2372 General Relativity - Lecture 5

0:00 What is spacetime? 20:20 Kinematics, basic definitions 35:18 Motion of test particles 41:18 Frequency shift of light 1:10:19 Simultaneity
13. ### I Einstein Definition of Simultaneity for Langevin Observers

Hi, reading this old thread Second postulate of SR quiz question I'd like to ask for a clarification on the following: Here the Einstein definition of simultaneity to a given event on the Langevin observer's worldline locally means take the events on the 3D spacelike orthogonal complement to...
14. ### I Simultaneity of accelerated clocks

<Moderators note: split from https://www.physicsforums.com/threads/is-the-relativity-of-simultaneity-more-than-just-a-fudge-factor.1012027/#post-6596771 > I have a (probably) stupid question. My rest frame contains myself and the usual rigid 3D array of clocks. I use Einstein's method to...
15. ### B Is the relativity of simultaneity more than just a fudge factor?

<Moderator’s note: a reference to an article published in a predatory journal has been removed. References on PF should be from the professional scientific literature or from other sources consistent with the professional scientific literature> I read through many posting on various threads in...
16. ### Special relativity - measure of a rod and simultaneity

Hi, I´m trying to solve a special relativity problem, and I think I need some help. There are two inertial frames of reference, ##O## and ##O'##, the last one moving with relative velocity ##v## in the ##x## direction. There's a rod with length ##L'## fixed to frame ##O'##, such that front end...
17. ### A Teaching SR without simultaneity

This thread, some earlier ones, and my signature got me thinking a bit about whether it would be a good idea to de-emphasize simultaneity when teaching SR since it is a frame dependent concept. I did not do much thinking myself yet but would like to hear people’s opinions and thoughts on how...
18. ### I Relative Simultaneity: Comparing 2 Incompatible Calculation Methods

Hello, Hope you had a merry Christmas, :wink: In order to deepen some knowledge on the notion of relative simultaneity, I studied a graph taken from a video, and the ages of the twins being very very rounded, I decided to make precise calculations using two methods different. I would like to...
19. ### I Global simultaneity surfaces - how to adjust proper time?

Hi, searching on PF I found this old post Global simultaneity surfaces. I read the book "General Relativity for Mathematicians"- Sachs and Wu section 2.3 - Reference frames (see the page attached). They define a congruence of worldlines as 'proper time synchronizable' iff there exist a...
20. ### Relativity and Simultaneity: A Cosmic Perspective

Posed question is that a comment plunges into Jupiter. Same time as my physics class starts on Earth. My friend is traveling towards Jupiter at a significant percentage of c. Would the person in spaceship say that the comment collision occurred before, after or as class started? My answer: same...
21. ### Special relativity and simultaneity: Spacecraft and Target

I made an exercise whose question is like that: A spacecraft moves with speed v at the axis x. There are two target at the axis x, in which the distance between them is L at the ground frame. Suppose that the spacecraft shoot the target simultaneously when it passes by the target. A|so...
22. ### Explaining Voltage Split in Series Circuits with Ohm's Law

Let us set up a very simple circuit, with two resistors in series as shown in the sketch. We know that for this particular circuit ##V_{14} = V_{12} + V_{23}##. But what I have always wondered is: How does the circuit "know" that once I introduce a battery of ##8 V## that each of the bulbs...
23. ### I Relativity of simultaneity doubt

(excuse me for my english, but I'm studying physics and I am not a native English speaker) One observer OE, is on the ground, we take him as the fixed frame of reference. The other OT is on the train that is moving relatively to the OE at a costant velocity ( they are both inertial frame of...
24. ### I Relativity of Simultaneity Questions

Hi All, I've been doing some reading on the above but having some problems understanding certain parts of it (maybe it's wrong from Wikipedia!) To simplify it for me I will first pose a simple scenario where we are not factoring in speed yet, then go from there. Say we have two planets A and B...
25. E

### A Exploring Epsilon Simultaneity: Advantages and Applications

What is the advantage of considering the generalised simultaneity criterion ##t = (1-\epsilon)t_1 + \epsilon t_2## for ##\epsilon## between ##0## and ##1##? How does varying the parameter ##\epsilon## help to elucidate the structure of the special theory? I think the surfaces of simultaneity are...
26. ### B Doubt about the relativity of simultaneity

(I hope my English is understood). Hello, I have a question regarding the relativity of simultaneity. The mean temperature of the cosmic microwave background tells us how big the universe is with respect to the recombination epoch. If I now measure that the mean temperature of the cosmic...
27. ### Unlocking the Power of Simultaneity: Tips for Taking the First Step

What is my first step here? I'm not sure of where to start?
28. ### I How Does Relativity of Simultaneity Clash w/Thermodynamics?

In special relativity, observers can disagree on the order of events - if Alice thinks events A, B and C are simultaneous, Bob can think A happened before B which happened before C, and Carlos thinks C happened before B which happened before A - provided A, B and C are not causally connected, of...
29. ### B Calculating Relativity of Simultaneity

The question is in reference to calculating relativity of simultaneity. I am on the step where I take the time in Alice's frame from the front and from the rear clock and minus it to the get the total time. I end up with gamma squared etc (For more details see the picture below) I have...
30. ### B Bell's theorem, QFT, and the Relativity of Simultaneity

I've been slowly grinding away with what I can about quantum mechanics and QFT. I'm not sure how far I've gotten but I've come up against a bit of a roadblock concerning how the relativity of simultaneity applies in QFT with specific reference to the outcome of Bell tests. My misunderstanding...
31. ### B Solving Doubts about Simultaneity Exp. in Special Relativity

I'm reading about how the concept of simultaneity breaks down in special relativity. Here's the relevant paragraph: ----- Consider a photon source ##C_0## in a train car situated equidistant between detectors ##C_1## and ##C_2##. The source emits photons back to back. In a reference frame at...
32. ### I The Simultaneity Paradox: Investigating Net Rotation of a Balanced Beam

Suppose there is a beam balanced on a fulcrum at its center of mass. One observer at rest with respect to the beam sees two lightning bolts strike the ends of the beam simultaneously, such that there is no net rotation of the beam. However, a moving inertial observer sees one bolt strike one...
33. ### I Relativity of Simultaneity: What Einstein's Contribution Was

Something that I consider very silly, yet I try to solve relates to the relativity of simultaneity. According to SR , two evevnts taking place in different positions along the line of relative motion of two inertial observers are not simultaneous in both frames. Now, I wanted to see how this...
34. ### B Simultaneity & Non-Invariant Variables: Is the Speed of Light Necessary?

The famous example demonstrating that simultaneity is an non-invariant variable would be the lighting bolts striking a fast moving train. Or a projector at a mid-point shooting off two beams at the same time to receivers on the opposite ends (for the person at rest and not on the train's...
35. ### I Observers A & B: Rest & Simultaneity

Suppose we have two observers A and B and they are at rest. Observer A observes two objects falling from height H (A has same distance between the two objects). Does observer B will measure different times for the duration of falling of the two objects ? (because the two object are not in the...
36. ### I Simultaneity of two light rays in different reference frames

I am studying the fact that two events that are simultaneous in a frame aren't (in general) simultaneous in another. The lamp is equidistant from the two ends. When the light is switched on an observer on the train sees how both light rays hit the back and the front of the train...
37. ### I Simultaneity on a moving train

Question from non-physicist. Hope there is a simple answer. In Einstein's thought experiment with moving train and embankment: If there is an observer in the middle of one of the train cars and one light beam is flashed from inside each side of the car (same location on each sides) towards the...
38. ### B Einstein's train and simultaneity

[Moderator's note: Spin off from previous thread: https://www.physicsforums.com/threads/is-the-andromeda-paradox-accepted-in-physics.960861/] There's just one thing I don't understand about all this, Einstein's train thought experiment. It basically states that an observer in a train moving...
39. ### I Is Simultaneity still alive in QM?

In Classical Mechanics, according to SR, the concept of simultaneity is dead, a meaningless concept. But in QM, entanglement implies that some limited form of simultaneity exists. If we have two particles correlated due to entanglement, a measurement of one particle immediately gives us the...
40. ### I Relativistic Simultaneity: A Thought Experiment

Hi guys, I've been asked to check somebody's relativity logic and i'd love to get s second opinion as it's easy to slip up. There is a train, with an observer (A) in the middle, with a device that fires marbles simultaneously up the train and down the train. There is also a...
41. ### I Simultaneity and the Twin Paradox

Here is a diagram from the Wikipedia. I'm sure you understand what this represents. Those who don't, can go to the Wikipedia page (https://en.wikipedia.org/wiki/Twin_paradox) and see all the details. After my prior post, I have a better appreciation for simultaneity. Originally, when I looked...
42. ### Relative Simultaneity: Free Resources to Help You Understand

Hello I'm having a lot of trouble understanding simultinaity and would appreciate any free book or article reccomendations.
43. ### B Einstein's Thought Experiment on Simultaneity | Newbie Q&A

Hello I am investigating a thought experiment conducted by Einstein in which he imagines a man on a train platform (it is being explained on a documentary I am watching). Two lightning bolts equidistant from him strike at either side. He sees these bolts of lighting strike at the same time. A...
44. ### I Relative Simultaneity: Flashlight in Moving Ship

Imagine you are in the center of a ship moving at V to the right relative to earth. You have a flashlight in your hand and two perfect reflectors on each end of the ship. If you turn on the flashlight will you observe the reflected light from both ends to hit you simultaneously? What will...
45. ### Special Relativity - Relativity of Simultaneity?

Homework Statement A thin rod of proper length 4a is traveling along the x-axis of a frame S with a speed ##{\frac {\sqrt 3} 2}c## in the positive x-direction. A hollow cylinder CD of proper length 2a is placed with its axis along the x-axis, so that when the ends of the cylinder are open the...
46. ### I Tangible example of relativity of simultaneity

I always liked the idea of starting relativity discussions with the idea that your father could travel at a substantial fraction of the speed of light and return back at roughly the same age as you. This makes time dilation seem interesting, and drives curiosity in students. But I'm struggling...
47. ### I Find Solutions to Helical Worldline's Surfaces of Simultaneity

For an inertial frame in flat spacetime with cartesian coordinates, and a particle in that frame whose worldline is a helix (moving in a circle at constant speed in x-y plane), given an arbitrary event with coordinates ##t##, ##x##, and ##y##, (we won’t worry about ##z##) how would I go about...
48. ### B I cannot grasp simultaneity in Special Relativity

Hi everyone, I'm struggling to grasp simultaneity in Special Relativity. Since I am struggling conceptually, I have posted my question here. But if you think this problem I made up modified should go to homework, I apologise (and feel free to move it). Suppose we have two light sources...
49. ### Simultaneity and diversity for water supply infrastructure

Hello, Is anyone familiar with the French Standard DTU for water supply infrastructure networks. I'm not understanding how to apply the diversity factors and coefficient of simultaneity to calculate the instantaneous maxumum demand and where to apply it. I was thinking of applying the formula...
50. ### B Solving the Mystery of Simultaneity: A Relativity Question

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...