Topics in Retrocausality

Swammerdami · Dec 13, 2020

Reports of, and scientific studies of, precognition will not go away. A future event causes something in its past! Here is a summary of some of the research: Precognition as a form of prospection: A review of the evidence.

A recent post at TFT linked to such a study. By chance(!?) I watched Tenet the next day. (I don't think it will spoil the movie to reveal that security forces engage in temporal pincer attacks with one team arriving at the end of the battle and moving backwards in time, using "inverted" weapons.) I decided a "Topics in Retrocausality" thread was needed. Let's start with fundamental physics. (I am not a physicist and hope someone will come along and clear up my confusions!)

(1) Space is isotropic.
The fundamental laws of physics are the same in any spatial direction. "Up" and "down" may seem very different to someone hanging precariously on a cliff, but that's due to local terrain (especially Earth's gravity) and is not a result of fundamental laws.

(2) Time is isotropic.
From the introduction of the paper linked above:

While taking this line of research seriously may seem beyond the pale to some, it is worth remembering that advances in psychology and physics have repeatedly demonstrated that everyday intuitions about the nature of reality only partially reflect the nature of reality itself. It is possible that such imprecise intuitions include the concept of a fixed “arrow of time,” which Einstein famously called a “stubbornly persistent illusion.”

The isotropy of time is said to be a necessary assumption of special relativity. Many physicists carefully avoid the use of words like cause and effect.

The fundamental laws of physics are the same in either direction. The equations of Gravity (whether Newton's or Einstein's), Maxwell, Dirac, Weyl, etc. do not "care" about time's direction. Let f() be the operator which predicts the universe (whether a list of particles, or wave functions) one second after the present universe, so that
. . . . . S_t+1 = f(S_t)
Then the same function can be applied in the other direction to predict the past!
. . . . . S^*_t-1 = f(S^*_t)
The substitution of S^* for S is to address some trivia:
(a) velocities must all be inverted. A train racing from Chicago to New York is racing from New York to Chicago when the video is played backwards.
(b) the vector associated with magnetic field must also be reversed.
(c) the spatial reflection (x,y,z) --> (x,z,y) can be imposed to counter a peculiarity of weak interactions.

We remember our past and plan our future, so time certainly doesn't seem isotropic! But perhaps, like the guy hanging on a cliff who doesn't think space is isotropic, the arrow of time we experience is a result of "local terrain."

(I know some of you are eager to pound on Reply and mention the Second Law of Thermodynamics. There will be much discussion of that "Law" in this thread, but for now just note that it is not a fundamental law. The equations of Maxwell, Einstein, etc. all do just fine without it!)

(3) Quantum computing
In an ordinary computer, 20 bits can represent any ONE of a million numbers. But in a new kid of computer, 20 qubits can represent ALL million numbers simultaneously. Computations are performed on all million numbers simultaneously; the wave functions later collapse around the number that fulfills a goal set by an algorithm like Shor's or Grover's. Is this not retrocausality, that future goal affecting which number the computation really acted on?

(4) Photosynthesis
Most of the Earth's biomass uses an almost magical chemical structure, featuring both magnesium and manganese ions, to harness energy. A particle of sunshine strips an electron from the magnesium in chlorophyll; the electron begins bouncing around. (A positively-charged "hole" is created when the electron is dislodged; that hole also bounces around.) The plant then "hopes" the electron will arrive at, and be put to use by, the manganese ion in a "reaction center" buried in a plethora of chlorophyll molecules.

In a classical model, most electrons would bounce at random and usually encounter their associated "hole" with the electronic energy then dissipated as waste heat. But instead, the electron and hole are quantum waves which explore various paths in parallel and "tunnel" to the manganese-based reaction center with almost 100% efficiency! I think this tunneling is quite analogous to Grover's algorithm for quantum computing!

(5) EPR and GHZ paradoxes resolved!
Bell's Theorem, and the "paradoxical" outcomes of the EPR and GHZ experiments are said to defy all common sense. In event A, 2 or 3 entangled photons are created; suppose these photons are sent to Venus (where one photon is measured with event B) and Mars (where event C measures the other photon). Event B seems to affect Event C, though those measurements can be timed so that any communication would need to travel faster than light. Almost everyone calls this unfathomable; proof that quantum physics "makes no sense"!

But all paradox disappears if we allow retrocausality. Event B creates a time-reversed photon which travels to A and affects its twin, which then travels to Event C. No paradox at all!

Huw Price writes that quantum physics with its seeming paradoxes is exactly what we should expect if our universe has time isotropy, if retrocausality is real.

I've not even mentioned the dreaded Second Law of Thermodynamics yet, nor the problem of advanced radiation, nor Boltzmann's interesting insights way back in the 19th century, but let's start from here.

But first, since the disappearance of the paradoxes of Bell's Theorem, etc. is IMO a strong argument for retrocausality, let's review one of those paradoxes. I find the (100%) GHZ "paradox" much clearer than the probabilities Bell's Theorem. Anyone who wades through this paper won't want or need my summary which, being a useless tangent, I've hidden.

Show

Jayjay · Dec 14, 2020

How can you tell whether B caused A and C, rather than C causing A and B? If the choice is arbitrary, what does causality even mean?

Swammerdami · Dec 15, 2020

Jayjay said:
How can you tell whether B caused A and C, rather than C causing A and B? If the choice is arbitrary, what does causality even mean?

Correct! As I mentioned already [(2) above], physicists who pursue these questions avoid using the words 'cause' and 'effect' altogether!

We certainly experience cause and effect in our macro-world. Watering the plants caused the flowers to bloom; we didn't water them because they bloomed in the future (or did we?). But these macro-events involve many quintillions of molecules acting somehow in unison; when we shrink down and watch just 2 or 3 molecules interacting, things aren't so clear.

The absolute distinction between past and future — the direction of Time's Arrow — is challenged by retrocausality. Yet the causality arrow is already sometimes reversed by philosophers, e.g. in Calvinism. I'll offer one cute example:
There is a nursery song in Thailand where the natural cause-effect relationship
. . . . . "Why does the frog croak? Why does the frog croak? It croaks because it rains."
is reversed to produce
. . . . . "Why does it rain? Why does it rain? It rains because the frog croaks."
(Unfortunately my Thai informants have no explanation for this reversal.)

Saint Augustine said:
What is time? If nobody asks me, I know; but if I were desirous to explain it to one that should ask me, plainly I know not.

Huw Price said:
the stock philosophical debates about time [] have not changed much since the time of Saint Augustine or even earlier.

At a 1991 conference on the Physical Origins of Time Asymmetry

Julian Barbour said:
During the Workshop, I conducted a very informal straw-poll, putting the following question to each of the 42 participants: Do you believe time is a truly basic concept that must appear in the foundations of any theory of the world, or is it an effective concept that can be derived from more primitive notions in the same way that a notion of temperature can be recovered in statistical mechanics?

The results were as follows: 20 said there was no time at a fundamental level, 12 declared themselves to be undecided or wished to abstain, and 10 believed time did exist at the most basic level. However, among the 12 in the undecided/abstain column, 5 were sympathetic to or inclined to the belief that time should not appear at the most basic level of theory.

I don't know whether Newton explicitly observed that his Laws of Motion and Gravitation were time-reversible. Pierre-Simon Marquis de Laplace noted this in the 18th century, and it was well-known by the 19th century, when the Second Law of Thermodynamics was developed:
. . . . . E^ntropy_t ≥ E^ntropy_t' whenever t ≥ t'
Time asymmetry derived statistically from the S_t+1 = f(S_t) mentioned in #1.
Yet we could derive the opposite inequality if we start with S^*_t-1 = f(S^*_t) ! (Sorry, S rather than E^ntropy is the usual symbol for entropy but I painted myself into a corner by using S else-wise in the first post. Well, at least you know now that this series of posts wasn't premeditated!

(Thermodynamics was developed before the Atomic theory was widely accepted, and some confusion will arise because of a distinction between "classical thermodynamics" and "statistical thermodynamics." Without objection let's please regard the latter as the correct theory.)

The physicists developing the Second Law were well aware of the paradox: How can we get time asymmetry in a law derived from time-symmetric axioms! Now might be the time to mention the bizarre notion of "Boltzmann brains", but I'll just close this post with some remarks from a famous Nobel Prize-winner.

Richard Feynman said:
So far as we know, all the fundamental laws of physics, such as Newton's equations, are reversible. Then were does irreversibility come from? It comes from order going to disorder, but we do not understand this until we know the origin of the order. Why is it that the situations we find ourselves in every day are always out of equilibrium?

One possible explanation is the following. Look again at our box of mixed white and black molecules. Now it is possible, if we wait long enough, by sheer, grossly improbable, but possible, accident, that the distribution of molecules gets to be mostly white on one side and mostly black on the other. After that, as time goes on and accidents continue, they get more mixed up again.

Thus one possible explanation of the high degree of order in the present-day world is that it is just a question of luck.

[But this doesn't seem to match the evidence.] We therefore conclude that the universe is not a fluctuation, and that the order is a memory of conditions when things started.... For some reason, the universe at one time [e.g. the Big Bang] had a very low entropy for its energy content, and since then the entropy has increased. So that is the way toward the future. That is the origin of all irreversibility, that is what makes the processes of growth and decay, that makes us remember the past and not the future, remember the things which are closer to that moment in history of the universe when the order was higher than now, and why we are not able to remember things where the disorder is higher than now, which we call the future.

Swammerdami · Dec 30, 2020

Continuing the list of topics:

(6) Time's Arrow derives from the low-entropy Big Bang.
Just as a swimmer is forced downstream by rushing water, so it is the rush of negative entropy from billions of years ago (and sunlight that set out 8 minutes ago) that lead to the apparent asymmetry in causality. Many or most theoretical physicists agree with Richard Feynman that this is the case.

(7) Gold Universe
The Big Bang serves as a boundary condition, from which the universe evolves according to the laws of physics. But what if there are TWO boundary conditions: A Big Bang 13+ billion years ago, and a Big Crunch in the far distant future? What if that Big Crunch was like a mirror image of the Big Bang, with negative entropy streaming backwards, so that creatures in the far far distant future would be experiencing a causality arrow pointed in the opposite direction from us?

Thomas Gold proposed this 50+ years ago; it was accepted as a serious possibility by Stephen Hawking and other experts. I think it's largely rejected today as not fitting observations: the universe is expected to keep expanding "forever," rather than collapsing into a Big Crunch. But is our understanding of Dark Matter and "Dark Energy" really good enough to be sure about the far distant future?

If creatures from a planet or an artificial spaceship from a far-distant Big Crunch could somehow survive long enough to encounter our galaxy, and interact with us, how would they appear to us? I think they would seem much weirder than the "inverted" soldiers presented in the Tenet film.

(8) Where is the advanced radiation?
Since Maxwell's laws are time-symmetric, electronic interactions that send radio waves (or light) forward in time, should also be sending waves toward the past! For every photon reaching us which set out from the Sun 8 minutes ago, shouldn't there be a photon traveling in the opposite direction which will reach the Sun 8 minutes from now? The

Wheeler–Feynman_absorber_theory seems to claim that all these "advanced waves" somehow cancel out. !!??!?????

But here I will stop and wait for help! :-{ Can one of our physicists help me understand this Wheeler–Feynman theory?

Swammerdami · Dec 31, 2020

Let me give my own understanding of advanced radiation. I'm starting to "tread on thin ice" but I think this is substantially correct.

Let us think strictly about particles: they are easier to understand than waves, at least for me. (Almost by definition, particles are just as valid a model as waves in particle-wave duality.) Richard Feynman also preferred to think about particles.

A photon is emitted (A) from the interior of the sun, heats an atom (B) near the sun's surface, which in turn transmits a photon to Earth where it collides (C) with the magnesium atom in a chlorophyll molecule. The sequence A->B->C is a normal past-to-future causal path, with the photons representing "retarded radiation."

So where is the "advanced radiation"? And if half the energy is spent on unobserved advanced radiation, the retarded radiation should be halved to conserve energy, but it isn't. The answer is ridiculously simple! The advanced radiation associated with (B) is the photon A->B, but simply viewed in reverse time. Similarly, the photon that traveled from sun to plant leaf in 8 minutes reverses path when it reverses time, so the advanced radiation from the chlorophyll finds the same atom, eight minutes ago, in sun's surface and provides the additional half of the photonic energy. Read about Wheeler–Feynman absorber theory and suffer through a multitude of tedious wave equations (magnetic fields and relativistic speeds need to be reconciled, etc.) but the underlying idea is trivial, at least when one thinks of particles rather than waves. Every photon does double-duty in a transaction: The photon associated with the ordinary retarded wave from (A) to (B) is the very photon associated with an advanced wave from (B) to (A).

So the "inverted" soldiers in the movie Tenet would NOT see a bright sun! The sunlight is all (or almost all) traveling in the wrong temporal direction for "inverted" eyes to see it.

And why is that? Does that mean that the interactions in sun's surface that produce sunlight are not time-symmetric? Again, it is statistical thermodynamics that comes to the rescue. The sun's surface receives its energy from the interior, so its advanced waves are needed for those transactions.

Does this make sense?

Topics in Retrocausality

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