[ExI] Is there an alternative to the block time view?

[Jason Resch]

(Splitting off this topic from a previous thread)

>       Do you think this is true? And since I am not a physicist, I make
> no claim, but
> >       just wanted to bring this to your attention.
> >
> > It is true they there remains a consistent notion of causality embedded
> within
> > the 4D structure of spacetime, but it is wrong when it says relativity
> remains
> > consistent with an objective passage of time.
> >
> > See this for a more detailed explanation of why relativity is
> incompatible
> > with a passage of time: https://philpapers.org/rec/PETITA
>
> I'm sorry, but I am not skilled enough and do not have time enough to
> argue this
> point. When it comes to relativity, causality and the passage of time, I
> have to
> let other list members who are way more skilled physicists than I am step
> in and
> continue the discussion from here. I can only say that based on what I
> see, it
> does not seem like it is settled.
>


It has been argued that Einstein's relativity rules out two conceptions of
time found in the philosophy of time
<https://www.preposterousuniverse.com/blog/2015/04/03/the-reality-of-time/>.
Those three possibilities are:

   - *presentism* (only a single point in time, the present, is real, past
   and future states are non-existent and have no reality).
   - *possibilism* (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).
   - *eternalism* (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")

See diagram:
https://cdn.alwaysasking.com/wp-content/uploads/2020/08/Three-Conceptions-of-Time.png

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.

*Some reference quotes:*

"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."
-- Briane Greene in “The Elegant Universe” (1999)

"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."
-- Albert Einstein in “Relativity: The Special and General Theory” 15th
edition (1952)

"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."
-- Hermann Minkowski in "Space and Time" (1909)

"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."
-- Kip Thorne in "What is Space-Time?
<https://www.youtube.com/watch?v=mvdlN4H4T54>" (2013)


*Some arguments:*

*The relativity of simultaneity*

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.
See: https://alwaysasking.com/what-is-time/#Relativity_of_Simultaneity

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).
See: https://alwaysasking.com/what-is-time/#Clock_Desynchronization

"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."
-- Albert Einstein in "Relativity: The Special and the General Theory"
(1916)

*Andromeda Paradox*

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.

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?

"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.
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.
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”?"
-- Roger Penrose, in “The Emperor’s New Mind” (1989)

"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."
-- Hilary Putnam in "Time and Physical Geometry" (1967)

See: https://alwaysasking.com/what-is-time/#The_Andromeda_paradox

Jason
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