[Travis Tremlee (OP)]

According to Einstein's equations of special relativity, the faster one moves through space, then the slower they move through time.
T = t/(1-(v/c)^2)^(1/2).

In general relativity, time near a massive object also slows down in accordance with the general relativity equation
T = t/(1-2GM/Rc^2)^(1/2)

Is a time machine an isolation machine? That is to say, quantum theory is not really about microscopic and sub-microscopic particles, it is about isolated things that do not interact with the external environment such that weird quantum effects can occur.

In that respect what we call a wormhole might be a form of macroscopic quantum tunneling.

How do we build a time machine?

So, when at rest, we are falling through the dimension of time at the speed of light. By moving faster and faster through space, time will slow down. For a rocket nearing the speed of light, processes slow down but it is a relative slow down so the people on the rocket do not realize they are practically frozen in time.

I have imagined the attempt to travel back in time must be analogous to falling up hill. It is not something that would occur naturally.

Going faster than the speed of light means going backwards in time. Of course, it is impossible for a material(matter) object to even reach the speed of light. It appears that the barrier to time travel into the past is mighty and impossible to cross.

But we most likely live in a multiverse of parallel realities. These realities might exist in a spectrum such that they are all infinitely close to each other – just as radio frequencies exist on a spectrum to be reached by tuning a radio dial.

There are some theories that propose our universe or "multiverse" is a gigantic quantum computer. Perhaps what time really is, might be analogous to a sequence of computational or statistical "shifting" from parallel reality to parallel reality. We usually do not notice any differences between the parallels because we are shifting to realities that are almost exactly like what we remember...

That would imply that the future and the past are in some form of communication or co-determination.

The future would in a sense would influence or help to determine the past...
 
Wormholes seem more like a quantum phenomena and macroscopic wormholes might be related to spinning black holes. Time dilation due to the intense gravity of black holes causes time to slow down and light to be extremely redshifted. The light cannot escape the event horizon of the black hole so its path becomes a circular... But the late Stephen Hawking described how particles can escape black holes through Hawking radiation which seems to describe something like quantum tunneling for the escapee particles and thus black holes also radiate. The smaller they are, the more they radiate. I suspect that wormholes can be described as a kind of macroscopic quantum tunneling ...hypothetically speaking...


The opening of a wormhole would resemble a sphere.

Still, the feeling of gravity from the black hole is communicated to observers outside the event horizon. The communication "escapes" the black hole it seems. I recall reading that there is no limit to how fast space-time itself can be stretched or contracted. That does raise the question about gravitons though. I have read science discussions online explaining that the reason communication for the feeling of gravity is felt outside of the black hole is that gravity is a geometric property of spacetime.

Communication across space cannot be faster than c, the speed of light. That is to say, communication in an inertial reference frame cannot be faster than the speed of light. But warp drive can hypothetically propel a spacecraft at multiples of c greater than 1.

They explain that gravitational waves – and thus gravitons, cannot travel faster than the speed of light either, so I am not completely sure about warp drive...

A wormhole takes a shortcut through hyperspace and I imagine the rules of hyperspace are different from the rules of our normal spacetime within this universe.

[Kryptid]

We usually do not notice any differences between the parallels because we are shifting to realities that are almost exactly like what we remember...

How could you know the difference?

Wormholes seem more like a quantum phenomena

It has been suggested that wormholes are form of quantum entanglement: https://www.zmescience.com/research/quantum-entanglement-wormholes-0424/#:~:text=New%20theory%20suggests%20quantum%20entanglement%20and%20wormholes%20are%20linked%20together,-byTibi%20Puiu&text=In%20a%20pair%20of%20entangled,are%20millions%20of%20miles%20away.

They explain that gravitational waves – and thus gravitons, cannot travel faster than the speed of light either, so I am not completely sure about warp drive...

That is indeed an objection that I've seen to a faster-than-light warp drive. You would need some way to send a signal to the space in front of you to tell it how to warp. If that signal is limited to the speed of light, that would seem to limit how fast the warp drive can go.

[puppypower]

The second law states that the entropy of the universe has to increase. This is why there is not perpetual motion. There is no such thing as perpetual motion, since although energy is conserved over time, entropy will increase over time. If we used a machine to go back into time, since it is not 100% efficient, we will add entropy to the past. This will change the past.

Entropy is a state variable, meaning for any given state of matter the entropy will be a fixed value.  Water at 25C and 1 atmosphere has a very specific measured entropy that is always the same for this state. Entropy has a connection to the facades of matter; state.

If we were to go to the past we add, at the very least, machine entropy. We would change the state or facade of the past to reflect the entropy increase that we have added. In essence this is not really the past, but a different past, that may not lead to our present. You may never be born in the present, since you would have already lived in the past. It never happened.

If your time machine was still working in the altered past, and you decide to go back to the present, you will add entropy to the present, when your arrive. Now the present is not the same since a new state will appear. It would still be interesting, but not what you might expect. You would need special training to be prepared for anything.

[Kryptid]

This will change the past.

Not necessarily: https://en.wikipedia.org/wiki/Novikov_self-consistency_principle