Talk:Rietdijk–Putnam argument

message: "If one of the people were walking towards the Andromeda Galaxy, then events in this galaxy might be hours or even days advanced of the events on Andromeda for the person walking in the other direction.[contradictory]"
It is not contradictory. It is the whole point of the argument! This is what special relativity tells us. Betaneptune (talk) 07:28, 9 September 2021 (UTC)
thread_title: contradictory

message: The names Rietdijk and Putnam occur only in the title. At the very least, to be in accordance with the Manual of Style, the article should begin in a fashion like this: "In late-night discussions on special relativity, the Rietdijk-Putnam argument is the argument that ...". That is, we need to see the name of the article back in some context. Then the name needs to be explained: "The argument is named after Penrose's two dogs, Rietdijk and Putname, who happened to be walking in opposite directions when he conceived of the argument." I'm not sure the references given meet the criterium of being reliable sources. -- --LambiamTalk 15:56, 28 September 2006 (UTC)
replies: text: Your problem of sources is now answered. The problem of whether or not the world is a nD manifold is central to physics. Why are you insulting such eminent scientists and philosophers as Penrose, Putnam and Rietdijk? Geometer 10:26, 13 October 2006 (UTC)
thread_title: Name

message: Nastyyy.. I only wanted to add an article to explain an interesting area of philosophy. I hate this edit warring business. I am out of here. Bye Geometer 08:26, 16 October 2006 (UTC)
replies: text: For heavens sake, I've removed the tag, without my concerns answered. But you're the best candidate to enhance this article. --Pjacobi 09:07, 16 October 2006 (UTC)
thread_title: Reversions - Edit war by [[User:Pjacobi|Pjacobi]]

message: The illustration of the Andromeda Paradox is explained only by reference to the Wiki article on Special Relativity and to a Wiki book.  The article on Special Relativity veers between the simplest example of relativity and mathematical theorems.  There is nothing apparent there (without studying the subject in depth) that provides the necessary reference to the example given in this article.  Could somone please either add a specific and detailed reference or provide a concise explanation for the example given?
LookingGlass (talk) 20:30, 18 October 2012 (UTC)
thread_title:  The relativity of simultaneity and the Andromeda paradox. 

message: The explanation in the diagram is backwards. In SR, the more one moves through space, the less one can move through time. Therefore it is Monday on Andromeda for the moving observer, and Tuesday for the stationary observer.  — Preceding unsigned comment added by Irthomasthomas (talk • contribs) 10:18, 13 July 2019 (UTC)
replies: text: It is even worse. The concept of an entity "moving in time" or "moving in space" is conceptually flawed, since the time as well as the space coordinates depend on the relative motion states of observers. There is no way to define "time" or "space" without fixing one observer and relating her coordinate system to another observer through a Lorentz transformation. Also, there is no such thing as a "stationary" observer.  — Preceding unsigned comment added by Tigelriegel (talk • contribs) 21:17, 17 January 2020 (UTC)

text: No, if the car is moving towards Andromeda, then it is later, Tuesday in this example, for the driver than for somebody standing next to the passing car (for whom it is Monday on Andromeda). [Btw, if the car is driving away from Andromeda, it's Sunday for the driver.] - The "in SR, the more one moves spatially, the less one moves through time" has nothing to do with it (the latter means that for the standing person, time is dilated in the car (and btw also the other way around)). But the diagram is still (and utterly) wrong because the coordinate system for the car is rotated to the left, instead of changed according to the Lorentz-transformation. Also, on Andromeda, Tuesday (with the decision made) comes before Monday (before the decision) in the diagram, which is obviously wrong. Relativity (and reality) doesn't work that way. --Felix Tritschler (talk) 16:13, 5 October 2020 (UTC)
thread_title:  Diagram is wrong 

message: In his presentation of the Andromeda Paradox, Roger Penrose made a fatal mistake when he states: "Then they can hark back to that chance encounter, and come to the conclusion that at that time, according to one of them, the decision lay in the uncertain future, while to the other, it lay in the certain past." 
At the time of their encounter both "see" -- if at all that would be possible -- and agree upon what has happened about 2.5 Mio years ago in the Andromeda Galaxy (which is about 2.5 Mio light years away from Earth) and not what happens there at the same time as both meet.
Thereby Penrose contradicts the two preceding sentences with the correct statements: "In fact neither of the people can yet know of the launching of the space fleet. They can know only later, when telescopic observations from Earth reveal that the fleet is indeed on its way."
This will be 2.5 Mio years after their encounter and then the two persons will disagree on what happens in Andromeda, if they keep their state of motion for the whole time, because then they will be several light days apart (about 4 light days, if their relative velocity is constantly 5 km/h for 2.5 Mio years in the direction of Andromeda). In this situation, however, they cannot communicate instantaneously anymore.
If the one closer to Andromeda, say Bob, would in the moment he sees the invasion fleet launching from Andromeda take his phone and call the second person, say John, to tell him about it, the phone signal would need under best conditions 4 light days to travel to John. So, when John hears his phone ring and picks up, the light of the invasion fleet launching towards the Earth would reach him in this moment, too, and he would agree to Bob: "Yes, you are right, I also see the invasion fleet leaving Andromeda". So, what?! Where is the paradox?
The fault in Roger Penrose's argument is to mix the two instances: the encounter of Bob and John in the park and the actual observation of the fleet launching from Andromeda by Bob 2.5 Mio years later at a location which is 4 light days away from the park where Bob and John had their encounter.
There is no relatevistic effect in this scenario other than the finite speed of light. No time dilatation or space contraction has to be taken into account, because the relative velocity for all protagonists (Bob, John, and the fleet commanders in the Andromeda Galaxy) is very small.
The formula to calculate the distance in light days between Bob and John after 2.5 Mio years can very easily be derived like this:
L  (distance to Andromeda): 2.5 Mio light years
t  (time for light to travel L): L/c = 2.5 Mio years
d  (distance between Bob and John after t for a relative velocity of v = 5 km/h): vL/c = 2,500,000 x 365.24 x 24 x 5 km
Δt (time light needs to travel d): (vL/c)/c = (2,500,000 x 365.24 x 24 x 5) km / (300,000 x 3,600 km/h) ≈ 0.8 x 24 x 5 light hours = 4 light days.Rolf108 (talk) 10:47, 18 November 2021 (UTC)
thread_title:  The catch in Roger Penrose's argument