<div dir="ltr"><div>(Splitting off this topic from a previous thread)</div><div><br></div><div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">>    Do you think this is true? And since I am not a physicist, I make no claim, but<br>>    just wanted to bring this to your attention.<br>><br>> It is true they there remains a consistent notion of causality embedded within<br>> the 4D structure of spacetime, but it is wrong when it says relativity remains<br>> consistent with an objective passage of time.<br>><br>> See this for a more detailed explanation of why relativity is incompatible<br>> with a passage of time: <a href="https://philpapers.org/rec/PETITA" rel="noreferrer" target="_blank">https://philpapers.org/rec/PETITA</a><br><br>I'm sorry, but I am not skilled enough and do not have time enough to argue this<br>point. When it comes to relativity, causality and the passage of time, I have to<br>let other list members who are way more skilled physicists than I am step in and<br>continue the discussion from here. I can only say that based on what I see, it<br>does not seem like it is settled.<br></blockquote><div><br></div></div><div><br></div><div>It has been argued that Einstein's relativity rules out two conceptions of time found in the <a href="https://www.preposterousuniverse.com/blog/2015/04/03/the-reality-of-time/">philosophy of time</a>. Those three possibilities are:</div><div><ul><li><b>presentism</b> (only a single point in time, the present, is real, past and future states are non-existent and have no reality).</li><li><b>possibilism</b> (the past and present are real, but the future is undetermined and not set in stone. Once the present catches up to a future time, it then becomes part of the eternal static past).</li><li><b>eternalism</b> (a.k.a. "block time", all points in time, past, present, and future, are equally real. There is no objective present, nor any objective flow of time. "present" is a word only with local, indexical meaning, like the word "here")</li></ul><div>See diagram: <a href="https://cdn.alwaysasking.com/wp-content/uploads/2020/08/Three-Conceptions-of-Time.png">https://cdn.alwaysasking.com/wp-content/uploads/2020/08/Three-Conceptions-of-Time.png</a></div><div><br></div><div>According to these arguments, relativity (even just special relativity) rules out presentism and possibilism, and establishes eternalism as the correct theory in the philosophy of time.</div></div><div><br></div><div><b><font size="4">Some reference quotes:</font></b></div><div><br></div><div>"Just as we envision all of space as really being out there, as really existing, we should also envision all of time as really being out there, as really existing too."<br>-- Briane Greene in “The Elegant Universe†(1999)<br></div><div><br></div><div>"It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence."<br>-- Albert Einstein in “Relativity: The Special and General Theory†15th edition (1952)<br></div><div><br></div><div>"The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality."<br>-- Hermann Minkowski in "Space and Time" (1909)<br></div><div><br></div><div>"So a physicist stepping back from our universe and thinking about it geometrically and mathematically, thinks of the entire universe as being an entity that we study from outside. And we have the entire future history, the entire past history, all of space and time, or unified spacetime as Minkowski would call it, and each point in [these] four dimensions, (1 time dimension and 3 space dimensions), and each point is an event. The birth of Abraham Lincoln occurred here, [...] his death occurred there, his assasination occurred there. During his life went through spacetime -- though this block universe, where each time represents an event. He went through spacetime through the beginning of the civil war on up to his ultimate death, moving through spacetime, and we describe his life by a curve in this 4-dimensional spacetime in this block universe."</div><div>-- Kip Thorne in "<a href="https://www.youtube.com/watch?v=mvdlN4H4T54">What is Space-Time?</a>" (2013)</div><div><br></div><div><br></div><div><b><font size="4">Some arguments:</font></b></div><div><br></div><div><b>The relativity of simultaneity</b> </div><div><br></div><div>A tenet of special relativity, the relativity of simultaneity refers to the fact that for two co-moving observers, Alice and Bob, an event that belongs in Alice's past, can be part of Bob's future, and vice versa. Two observers can even disagree on the relative order of a series of events. This is impossible if there is a single objective present.</div><div>See: <a href="https://alwaysasking.com/what-is-time/#Relativity_of_Simultaneity">https://alwaysasking.com/what-is-time/#Relativity_of_Simultaneity</a></div><div><br></div><div>A related phenomenon known as clock desynchronization occurs when an object undergoes length contraction: part of the object's proper length reaches through, and extends through time. A rocket ship with clocks in the front and ear of the rocket that are synchronized when the rocket is still, will become desynchronized when the rocket is in relative motion. The object actually stretches across time (the front of the rocket is behind in time compared to the rear of the rocket).</div><div>See: <a href="https://alwaysasking.com/what-is-time/#Clock_Desynchronization">https://alwaysasking.com/what-is-time/#Clock_Desynchronization</a></div><div><br></div><div>"Are two events (e.g. the two strokes of lightning A and B) which are simultaneous with reference to the railway embankment also simultaneous relatively to the train? We shall show directly that the answer must be in the negative."<br>-- Albert Einstein in "Relativity: The Special and the General Theory" (1916)<br></div><div><br></div><div><b>Andromeda Paradox</b></div><div><br></div><div>Roger Penrose came up with a brilliant thought experiment to illustrate this, known as the Andromeda Paradox. In this, two observers, walking in opposite directions pass each other on the sidewalk.</div><div><br></div><div>Due to their different relative motions, they belong to "presents" defined by different cross sections through 4d spacetime. In one person's present, the Andomedeans are still debating in their congress whether or not to invade the milky way. While in the other person's present, the Andomedeans have already voted and are already on their way. How is this possible?</div><div><br></div><div>"Two people pass each other on the street; and according to one of the two people, an Andromedean space fleet has already set off on its journey, while to the other, the decision as to whether or not the journey will actually take place has not yet been made.</div>How can there still be some uncertainty as to the outcome of that decision? If to either person the decision has already been made, then surely there cannot be any uncertainty. The launching of the space fleet is an inevitability. 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.<br>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. Was there then any uncertainty about that future? Or was the future of both people already “fixed�"<br>-- Roger Penrose, in “The Emperor’s New Mind†(1989)<div><br></div><div>"I conclude that the problem of the reality and the determinateness of future events is now solved. Moreover it is solved by physics and not by philosophy. We have learned that we live in a four-dimensional and not a three-dimensional world, and that space and time–or, better, space-like separations and time-like separations–are just two aspects of a single four-dimensional continuum."<br>-- Hilary Putnam in "Time and Physical Geometry" (1967)</div><div><br></div><div>See: <a href="https://alwaysasking.com/what-is-time/#The_Andromeda_paradox">https://alwaysasking.com/what-is-time/#The_Andromeda_paradox</a><br></div><div><br></div><div>Jason</div></div>