Bohmian mechanics, multiverse and block universe: past, the present and future all exist together

Albert Einstein firmly believed that humans were trapped in time, much like insects in fossilized resin. He proposed that every instant was predetermined, and each action was a consequence of a preceding action. In his view, individuals had no reins over their lives, merely the ability to observe. The illusion of making choices was just that - an illusion. He professed that life was predetermined before birth.

Had Einstein practiced Christianity, he would have likely been a Calvinist, subscribing to the doctrine that God predestines salvation or damnation before birth. Instead, he embraced the deterministic views of the Jewish philosopher, Spinoza, believing that time was merely a dimension where God orchestrated events.

Einstein's deterministic concepts of time persist to this day. His resistance against any physics that contradicted his philosophy is well-documented, as evidenced by his criticisms of Niels Bohr's quantum mechanics and the theory's predictions of random cosmic events, which clashed with his deterministic beliefs. The famous paraphrased quote, "God does not play dice," encapsulates his views.

Challenging our understanding of the universe, an antiquated theory

An ancient yet peculiar interpretation of quantum physics is resurfacing, threatening to undermine Einstein's theories more than the original ever did. If proven accurate, it could potentially debunk the notion of the past and future being fixed entities, as well as theories such as the multiverse and parallel universes housing diverse versions of ourselves. David Bohm articulated this theory in 1952.

Common knowledge dictates that quantum particles like electrons and photons lack fixed locations or speeds until observed. Quantum mechanics suggests they possess a wave function. According to Niels Bohr's popular interpretation, the act of observation collapses their wave functions, causing them to manifest as particles. This theory is substantiated by experiments like the double-slit experiment, where single particles fired at two slits behave like waves when allowed to hit a detector, but act like particles when intercepted and passed through a specific slit.

Both Einstein and Bohm countered this by arguing that hidden information must determine particle positions and that their appearances were not as random as Bohr claimed. Bohm sought a solution and offered the most bizarre yet somehow convincing interpretation of quantum mechanics, known as "Bohmian mechanics."

Bohmian Mechanics: An Unorthodox Interpretation of Quantum Physics

Bohmian mechanics, also known as the de Broglie-Bohm theory, offers a unique interpretation of quantum mechanics. In this theory, particles such as atoms and electrons are described by a quantum wave function, similar to the Bohr model. However, this is where Bohmian mechanics diverges from the standard quantum theory. In Bohm's model, every particle's position holds a specific value, regardless of whether it's being observed or not. This value is dictated by another function Bohm identified as the Q function, or the guiding function.

The Q function represents the concealed information that Einstein sought for his theories. The deterministic nature of Bohmian mechanics resonated with Einstein's own deterministic views, as it mirrored all predictions made by quantum mechanics. It eliminated the uncertainties associated with wave function collapse and particle positions, and didn't necessitate the existence of a multiverse to provide explanations.

However, Bohmian mechanics carried one aspect that Einstein strongly disagreed with - nonlocality. According to Bohm's theory, each particle's movement, guided by the Q function, depends on the movement of every other particle in the universe, all at once. Even though the particles themselves are local, their interactions with others are entirely nonlocal, thus violating the speed of light constraints.

When you integrate Bohmian mechanics with Einstein's theory of relativity, you end up with an intriguing blend called quantum field theory (QFT). QFT is used to interpret the outcomes of particle collisions in accelerators. Conventional QFT involves operators that depict the creation and annihilation of particles. However, in Bohmian QFT, there's no such occurrence. Instead, particles seem to magically jump from one position to another, giving the illusion of teleportation within the guiding function.

Bohmian mechanics and QFT propose that the entire particle universe shares a single present time, but argue that it's impossible to discern what that present time is. Only the guiding function has this knowledge, and it remains invisible to us. The universe continues to evolve from moment to moment, disregarding Einstein's relativity, but it only allows us to perceive the present at our precise location.

Eternalists vs. Presentists: A Quantum Perspective

Eternalists, including Einstein, propose a block universe theory. They envision the universe as a massive four-dimensional block where events occur, regardless of their randomness – it's all irrevocably "etched in stone." Some eternalists even propose a "growing" block universe, where the past is fixed, but the future remains uncertain.

On the other hand, presentists argue that only the present moment exists, with the past erased and the future not yet inscribed.

Suppose we liken time to a highway. Determinist Eternalists, like Einstein, see us as mere passengers in a self-driving car. While we might have a steering wheel and pedals, the car navigates itself. Going back in time would mean exiting the highway and returning to a previous point. However, our predetermined actions prevent us from altering the past. Some Eternalists believe in free will, but reconciling it with a pre-set future is challenging.

Presentists, conversely, see time as a car in a simulator. While the simulator remains static, it creates the illusion of temporal movement. The "past" is deleted from the simulator's memory, and the future is yet to be computed. Only the present exists.

Before Einstein, Newton had his views about time, likening the universe to a clock, with time flowing and mechanisms harmoniously interacting. Presentists might argue that this clockwork universe perfectly represents the single existing present moment.

Einstein's theory of relativity cast doubts on presentist beliefs, suggesting we can't agree with another person about what the present moment is. For instance, we can't agree that two events occur simultaneously if they're moving relative to each other.

In quantum physics, the rules of relativity don't always apply. Instead, particles can nonlocally influence each other, despite interpretation. While we can't send information faster than light, we can observe particles influencing each other at superluminal speeds.

This raises the question: Do particles influence each other simultaneously? How can this coincide with Einstein's theory denying such a phenomenon?

In the multiverse interpretation of quantum physics, particles affect each other by existing in different places in various universes. It's as if we have multiple copies of the same car traveling on different lanes, with cars appearing and disappearing at random. Sometimes a car splits into two bikes, then merges back into a car. They all collide until observed, causing the lanes to split into separate highways.

Bohmian mechanics suggest our cars travel along the time highway, but they're part of a larger machine, the guiding function. If it's a large car, it might as well be a giant simulator. We navigate our simulator along with everyone else. We can't know precisely what's happening to others in the simulator, as the simulation sometimes makes us vanish from one place and reappear in another. There are no divisions into different highways or machines appearing from nowhere. Instead, our lives unfold within the guiding function determining our reality, always remaining in the present moment. Our universe is simply structured in this way.

The present is described as a 3-D "hypersurface" within a "foliation" of spacetime. A hypersurface is like a surface but in more than two dimensions.

Bohmian mechanics is attractive because it does not need ideas such as wave function collapse, multiverse or even past and future. It restores something of the Newtonian idea of absolute time without violating the theory of relativity at the scale of the universe. It also does not rely on the creation and destruction of particles like quantum field theory, which is an interesting feature, since it is easier to think of particles instead of abstract, imaginary fields that spontaneously create things whenever they are disturbed with sufficient energy.

For now, we cannot distinguish between this and any of the other interpretations of quantum mechanics, but a quantum theory of gravity could make a difference.