## Presentism and simultaneity

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Presentism is the position that all that exists, exists in the present. Though one can speak of the past, and of events in the past, strictly speaking (in this position), there is no temporal event located there, that we are strictly referring to (as opposed to a memory of); and the same, or so for the future.

But what is present?

That which is present right here, right now; I mean by this: this now, this time on the clock, on this table, this morning; and all that is simultaneous with this now.

This, taking into account a little physics (I mean special and not general relativity) is justified locally; for the concept of simultaneity is still possible then.

So I can talk about now - in this room, or a little further away - on this earth.

But for distant places, which will be moving in some way to where I am here now, the concept of simultaneity fails.

Thus does presentism fail? (I mean for this reason; and not for others - since there are others).

This can be fixed - I think - if we take into account how some thing, or place (say, a star or galaxy) is moving in relation to us (since the concept of simultaneity is not absolute, but relational).

In this sense, it seems we can fix up the notion of what is present to me now, not just here, in my room; or a little further - on this earth; but everywhere.

But is this correct?

1Yes, it's an argument put forward by Putnam. You need a particular foliation of the universe to make sense of a present in relativity. Some argue that there is one, based on cosmic time. – Quentin Ruyant – 2016-06-01T15:10:31.960

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I think that according to special relativity, there is no now somewhere else, regardless of the distance, at least as long as we are not talking of quantum mechanics scales, "now" is only "here".

This is how Feynman puts it: "Alpha Centauri 'now' is an idea or concept of our mind; it is not something that is really definable physically at the moment." but the point is that it does not matter if we are talking of another galaxy or another continent, or another city or another room.

the tip of a light cone is just a point in space-time and any event outside the light cone has no fact-of-the-matter time order relation to it, regardless of the distance.

it is actually a mind blowing property of space-time, that we do not appreciate enough.

naturally, we have a little complexity in that the brain is about 10-15 cm in diameter, a problem that can be exploited for an indeterminate amount of contemplation.

you may be thinking now, "what is this guy talking about? didn't he hear of relative simultaneity?"

The planes of relative simultaneity are useful as mathematical abstractions but do not fit the bill of a Now. try to think about it while walking back and forth in your room, contemplating deeply what some hypothetical aliens are doing right now 2.5M light years away (on the axis of your march), but note that this remote Now of yours absurdly shifts back and forth days or even weeks each time you change direction. this problem is called the Andromeda Paradox.

as for presentism, it seems to me that things that have ceased to exist in your past light cone, like Socrates, do not exist (anymore), and things that will come into being in your future light cone, like the philosophers of the 31st century, do not exist (yet), and as for events outside your light cone, it is meaningless to ask if they have already happened or not.

there is no such thing as a snapshot of existence in the universe.

'Present to me now'; sounds quite physical to me; but it isn't the usual language of physics, I agree: I'm just choosing a specific position and time. – Mozibur Ullah – 2015-09-12T09:32:08.697

@MoziburUllah, right, I edited the answer. – nir – 2015-09-12T10:51:10.560

@JohnAm, simultaneity depends on the reference frame in the sense of mathematical analysis or as (I think Einstein put it) a matter of convention; I don't think that it has any bearing on the nature or "real" state of the world. if you take that convention too seriously you end up with the Andromeda paradox

– nir – 2015-09-12T11:04:23.570

1the article on the andromeda paradox early on mentions 'the plane of simultaneity'; this, I think is what I'm referring to above. – Mozibur Ullah – 2015-09-12T12:38:50.813

@nir: I do realise that presentism fails for the 'Andromeda paradox' - I wrote it fails for 'other reasons'; it's why I specifically wanted to focus on relative simultaneity; thanks for verifying that. – Mozibur Ullah – 2015-09-12T20:17:40.340

if Einstein talked about the illusion of the past, of the present and the future, i 'm pretty sure at the time of his death when he encountered the past that he had once wishfully denied, when he understood that the future welcomes him no more, and that the entrance of the welcoming present found impregnable locked, then at that specific moment he must have laughed ironically looking back to the bold leap he has taken in a figure of speech. – John Am – 2015-09-13T10:01:36.853

@JohnAm, while I don't believe in eternalism, I don't know how we may be able to communicate if you are pretty sure what Einstein must have experienced on his death bed - I'm for example pretty sure that you have no idea what he was thinking of. – nir – 2015-09-13T10:38:56.213

Don't read it literally. – John Am – 2015-09-13T10:42:39.713

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Comments are not for extended discussion; this conversation has been moved to chat.

– Joseph Weissman – 2015-09-14T00:16:03.567

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The OP writes:

So I can talk about now - in this room, ...

But for distant places, which will be moving in some way [relative] to where I am here now, the concept of simultaneity fails?

Thus does presentism fail? (I mean for this reason; and not for others - since there are others).

"For distant places ... " - in the present moment they are unobservable, but exist nevertheless. "Which are moving ..." - movement does not affect the "plane of simultaneity". Nothing can move anywhere in 'a moment', and the present is a moment.

As for "presentism". With the discovery of relativity one form of presentism was ended. Nevertheless, another remains. The superseded form is summed up by Vesselin Petkov in this article:

Is There an Alternative to the Block Universe View?

If one can talk about a widely (explicitly or implicitly) accepted view on reality it is presentism – the view that it is only the present (the three-dimensional world at the moment now') that exists. This common-sense view, which reflects the way we perceive the world, has two defining features: (i) the world exists only at the constantly changing present moment (past and future do not exist) and (ii) the world is three-dimensional.

The defining feature of special relativity is that the universe is not three-dimensional, so pre-relativistic presentism is incorrect. Simultaneity and the present are not extinguished though. For example, observers (O & O) moving in different frames can see equidistant events (e.g. A) simultaneously, as illustrated in the diagram below. Their movement is actually irrelevant.

An observer can see events in their past light cone, and signal to events in their future light cone. Spacetime outside the light cones, termed 'spacelike', is unobservable, yet there still exist the hypersurface of simultaneity, which is the present.

Richard Feynman somewhat confuses the issue in the quote below from "The Feynman Lectures on Physics, Vol. I, 17-3 Past, present and future". Nevertheless, the unobservability of the present does not affect its existence.

So distant events in the present are unobservable, but the present still exists. Just because we cannot see these distant events in the present does not mean their temporal simultaneity is disrupted one iota.

The only way modern, post-relativistic presentism is broken is by time-travel, which is highly speculative at best. In the example below the past and the present coexist, which contradicts modern presentism.

https://en.wikipedia.org/wiki/Wormhole#Time_travel

The theory of general relativity predicts that if traversable wormholes exist, they can also alter the speed of time. They could allow time travel.[3] This would be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox. However, time connects differently through the wormhole than outside it, so that synchronized clocks at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around.[25] This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry.

For example, consider two clocks at both mouths both showing the date as 2000. After being taken on a trip at relativistic velocities, the accelerated mouth is brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2004 while the stationary mouth's clock read 2012. A traveler who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2004, in the same region but now eight years in the past.

Summary

The defining feature of modern presentism is: (i) the world exists only at the constantly changing present moment (past and future do not exist).

The OP concludes:

But for distant places, which will be moving in some way to where I am here now, the concept of simultaneity fails.

This can be fixed - I think - if we take into account how some thing, or place (say, a star or galaxy) is moving in relation to us (since the concept of simultaneity is not absolute, but relational).

In this sense, it seems we can fix up the notion of what is present to me now, not just here, in my room; or a little further - on this earth; but everywhere.

But is this correct?

No, it is not correct, but the "notion of what is present to me now, ... or everywhere" is fixed by modern presentism, as described.

Although the distant present is unobservable, (and if it does later become observable cannot be agreed on for retrospective simultaneity due to observers having no privileged frame), it has temporal simultaneity, otherwise different times could exist at the same time, as in recipe for time-travel.

"Spacetime outside the light cones, termed 'spacelike', is unobservable, yet there still exist the hypersurface of simultaneity, which is the present". No, there does not exist "the hypersurface", there exist multiple spacelike hypersurfaces with no intrinsic way to single out one of them. Privileging one of them amounts to reintroducing Lorentz's ether, which is logically possible, but so ad hoc that presentists resorting to that would look desperate. Fortunately, they don't have to. We have no intuition of now, only of here-now, so presentist ontology needs no global simultaneity. – Conifold – 2017-04-24T23:56:12.527

Suppose two philosophers A and B here on earth arguing about another universe U with its own space-time. A says: "surely universe U can be said to exist Now — it presently exist — universe U exists in our present moment". and B says: "Nonsense! universe U is not in our space-time and therefore it is utterly meaningless and nonsensical to say it exists at the present moment!" Who do you think is right? – nir – 2016-06-02T07:17:06.123

@nir I have updated my answer. Please note the "hypersurface of simultaneity". – Chris Degnen – 2016-06-08T09:56:15.887

The paragraph ending with "Their movement is actually irrelevant." is wrong. also, what are you trying to say? that there exists a priviledged absolute plane of simultaneity? if not then it is not clear what it is that you mean by present moment. btw, I think petkov is wrong. Throughout his paper it seems that he assumes that for each observer, simultaneous events are in some sense metaphysically simultaneous or "really" simultaneous, while in fact, these are simply events that take place when synchronized clocks tick a particular time. – nir – 2016-06-08T17:34:10.420

I do not think that we will ever agree on this subject. – nir – 2016-06-08T17:34:25.343

@nir I'm also discussing this on Physics Stackexchange. Actually getting somewhere. (See the comments).

– Chris Degnen – 2016-06-08T17:46:22.677

it seems to me they are all trying to tell you the same thing that you do not want to hear. you have a strong intuition that there must exist such a thing as a present moment, but there is no basis for this intuition in physics. I am not saying it is a simple thing to realize. on the contrary - it is mind bending. nature is utterly mysterious. surely the moon exists, doesn't it? but what does it even mean to say it exists, other than that it exists now, at the present? but alas, there is no now-somewhere else in physics. ouch. – nir – 2016-06-08T18:42:34.337

@nir As I commented on Physics, when Feynman says ""There is no one who can tell us what is really happening right now, at any reasonable distance ..." he means the metaphysical concept "right now". I'm ok with that. It confirms that Philosophy Stackexchange is the correct place for this discussion. – Chris Degnen – 2016-06-08T19:18:29.347

@nir I'm not totally adamant that the present exists (without temporal irregularity). The thought that time-travel could be possible is quite intriguing. However, trying to discuss the concept of the moment Now seems second only to debating the meaning of Nothing. – Chris Degnen – 2016-06-08T19:40:24.997

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"Simultaneity" happens all the time (so to speak.) For example a "fortuitous" encounter is the chance meeting of someone expected to meet in the future that does in fact happen but not according to any plan or "foresight." There is also "spontaneity" where you are "acting" in present time but not really "knowing" where you are going with whatever it is you're thinking or are uncertain as to the outcome. There is also the idea of "serendipity"... a chance meeting that seems to assure one's "future" for all time. These and many other "facts of living" prove that while presentism existsit is only a construct of the mind and not in fact how we as humans nor any other sentient being in fact exists. Birds build nests, whales sing songs...all with a "future purpose" in mind (having shelter, getting food, etc)

Humans are unique in explicitly doing away with time in order to discover "truths" however. The technical term I believe is called "instinct" or in sports "being in the zone" where you are not conscious of time when "acting." For example we have yet to discover any other living organism that attempts to build something like a Cathedral...which we know will require generations or "not in our time" to be completed. This is a unique form of "presentism" as it requires a type of plan that can be understood in the here and now AND in the future thus implying some type of "Master Plan" or "destiny." Of course if I take a well worn footpath and turn it into a road and then some type of highway or "interchange" this might seem to imply some greater intelligence on my part but in reality I'm just trodding the same path and merely expanding (or expounding) on the possibilities should I consider more doing the same. This "more of the same" is neither in the present nor having to do with "simultaneity" but simply projecting out "into the future" what is merely observed. Technically speaking such "thinking" is false as if everything is "just a roll of the dice" the "odds" are still the same...namely the number is the number observed not the odds of said number "going to be observed."

One could argue and be right however if the dice are rolled and two sixes appear every time that "there is a problem with the dice." As Einstein famously said "God does not play dice with the Planets."