There is only the present moment. This isn’t philosophical mumbo-jumbo, I mean physically, time is a single point.
It’s completely different than our modern conception of time, which started when Minkowski space, originally used for Maxwell’s equations of electromagnetism, was adopted by Minkowski’s former student Einstein as the geometric basis for Relativity in the early 20th century. At first Einstein treated it as a mathematical convenience; later he came to adopt it as physical reality.
The history of science is full of cases where something was introduced as a mathematical convenience and later people decided it was physically real. Atoms were treated as a convenience by European alchemists and scientists but eventually they decided they were real things. (The ancient Greeks thought atoms were real, but they also thought object archetypes were real (the ideal chair, the ideal horse, etc). With atoms they didn’t advance beyond approx the Periodic Table stage, where atoms can still be just functional concepts. It was Einstein’s analysis of Brownian motion that put the nail in the coffin. Though some prominent physicists continued to debate it!) Light quanta (photons) were treated as a mere mathematical tool when introduced to solve the ultraviolet catastrophe. Same with atomic orbitals of electrons, the wave nature of particles, and renormalization (not accorded physical status exactly but still embraced as description of reality). This tendency to see what works mathematically as more than just math but indeed reality has been fruitful.
In Minkowski space, time is an extended, more-or-less infinite linear dimension perpendicular to the three space dimensions. This view of spacetime, in particular the extended laid-out-to-view nature of time, is not only baked into most of physics but has become part of popular culture. It’s great as a mathematical tool and to help us visualize things, not only for relatively but also in all areas of life: economics, business planning, thinking about our own lives, etc.
But I believe this particular bridge is one too far – as a description of reality, Minkowski space is wrong. Time is just one point.
Loop quantum gravity does away with the time dimension and space dimensions too. I was heartened when I found this out! I’d been planning for decades for relativity without time, though only recently toyed with throwing out space too. It’s clear now that both of these aren’t real, or at least they’re not what Minkowski space say they are. Pretty sure I’m still behind the loop quantum gravity people on this.
Advantages…
No need to wonder why time travel is allowed in physics but has never been observed and would cause all kinds of logical conundrums and causality violations anyway.
No need to wonder why time can’t move the other direction. It’s not moving any direction.
No need to wonder why it seems like there are two different kinds of time: the time dimension, and how fast things are moving in the time dimension!
Disadvantages…
Need to rework Relativity. No sweat, hang on a bit…
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