As a layperson, time travel seems impossible to me. Prove me wrong!

Yes, you identified a problem!

The four dimensions are the three dimensions of space and the one dimension of time.

Einstein showed that the Newtonian model of space being separate from time is just not how this universe works. What we have is space-time.

We can't separate the x axis from the y and z axes. And, it is just as impossible to separate time from space-time.

That was Einstein's contribution. That IS fundamental to the standard model of physics that is accepted universally today.

After saying "4 dimensions" that post went on to say that time is NOT a dimension!! Oops!

 

The things are concrete, that which gives the things meaning, identity, exist in the abstract.

 

I agree. In fact, I'd point out that we can talk about the measurements we make just like we can talk about numbers, rocks, photons and anything else.

So, I really don't see a line of any kind. In fact, if anyone actually thought about it that way, it seems like it would be a roadblock to progress, not a help.

Also, there IS a definition of abstract that human beings use ALL THE TIME without even thinking about it.

We commonly create abstractions of objects - like we have looked at a lot of doors, and have an abstraction of "door" that can be usefully applied and that we can all refer to. Even small children have created thousands of abstractions and they can discuss those effectively, just as if they are the real article.

 

Well, recall that the conversation began by my suggesting that time travel, in the HG Wells sci fi sense, is impossible, given that the past, and the future do not exist in the concrete sense, they exist solely in the abstract, and by virtue of the fact that a machine, in my lay opinion, cannot travel to the abstract, time travel in the Wells sense is impossible, whereupon I asked to be proven wrong on that point.

This contention by me triggered the marathon conversation on what I meant by 'exist in the abstract'

 

I only posted it because of a google query, and that was dished up, which, of course, could be wrong.

 

They are ALL things.

I haven't seen a reference to something that isn't a thing.

The standard model of physics is a thing. The abstraction of a triangle is a thing. All these things can be referenced in exactly the same was as physical objects are referenced.

But, more than that one doesn't get to see ANY of the things that so many people work with. They are ALL basically piles of data. Stars are arrays of numbers collected by some highly specialized collector.

In particle physics what one gets is terabytes of data which is then subjected to statistical analysis.

In quantum mechanics one has to deal with a statistical representation of location, and that is what one gets to work on.

 

Yes.

I cited a model of space-time that is accepted by physicists.

 

That model, as I understand it, does not conflict with the following concept:

The past did exist, and the future will exist.

They do exist, however, in the mind (which, if such find their way in print, doesn't change the fact)

I realize that physics doesn't address issues concerning the mind.

It's still true, however, even if the postulate is philosophical.

 

Have you read Number of the Beast, or Pursuit of the Pankara? Both by Heinlein. In it he postulates 6 dimensions: 3 space related axis and 3 time related one. Quite an interesting read.

 

Hmm... who cares. So many folks get wrapped up about consequential deviations, the effectiveness of traveling time would end in disaster. Why? Who does the traveling? People. And should people not be tempted to change outcomes in past eras to "improve" future outcomes for them? It seems only natural. So, why waste the time doing something that we know ends horribly wrong?

 

Physics addresses everything, doesn't it? How could physics ignore part of this universe.

Instead of saying "in the mind" why not just say "remembered" for the past and something more like "suspected based on current conditions and past experience" for the future.

 

What if space can be folded? What if time/space dimensions run parallel?

 

There are various models created by theoretical physicists that include a LOT of dimensions - like, at least a dozen for some!! I really don't know what to think about that. But, if there is a multiverse it can't all be in our dimensions, that's for sure!

As to the scifi, I do have a lot of respect for the genre and for the authors you mention, but I really don't read much scifi - not even most of the classics. I'm probably missing out.

 

Well, the past and future exist in the abstract, the mind, or however you choose to describe it, it means the same thing.

The entire point of raising that point is that, in my lay opinion, machine cannot travel to a mental picture, past or future.

So, if someone can prove me wrong on that point, I welcome it.

If there is proof, it would have to establish that the past and future do exist in some other dimension hitherto not discovered, or something like that, or something that quantum physics can shed light upon.

However, if my contention that the past and future are just pictures in the mind, accurate recollections or fanciful musings, how can a machine travel to them?

 

This isn't physics, though.

 

Well, do the past and the future exist in the mind, or not?

 

In Jack Finney's book Time and Again that is pretty much exactly how he accomplishes time travel. That is, he creates a picture of the year 1882 exact in every tiny detail in a warehouse and then places the subject in it. His belief does the rest.

I don't think that would work for a minute but Finney makes a good story.

Roger Penrose seems to ascribe to this theory, at least theoretically

 

That's a great question, and we don't really know for certain. There are several quantum phenomena that seem to suggest or imply the past and future exist, but to actually find out would be very technologically and pragmatically difficult for a variety or reasons.

 

What are they?

 

Well I would have to keep changing my clothes for instance.
Diapers at 150 years old isn't a good look...

 

Works for me.

 

I don't have a clue as to what that means to you.

If you mean, "Can we think about the future an the past?", I'd say obviously so. Every healthy human does that that constantly throughout every day.

If you mean, "Is there a specific past that absolutely did happen?", I'd say obviously so.

And, I'd point out that we can discuss the past, present and future just like we can discuss anything else. So, if you want to claim that these are ONLY in the "mind", I'd say that regardless of what you mean by that I would say absolutely not. We share them. We talk about them. We can test them. They are real.

 

Great question. This might be much more complicated than you really want to know, or take too much effort for me to explain here.

You might be familiar with the phenomena of interference. It seems two particles (or photons) will never set off in the same direction if those particles would then be destined to interfere with each other in a 'destructive' way. Normally we know that which direction the particle would take off in will be random, but actually we know it is not entirely random. The particles seem to have some way of knowing what will happen in the future, and will not set off on their adventure if they do not like what would happen if they set out in that exact direction.

This implies that particles behave like "strings" through time. And why don't particles go certain directions? Because the strings can't "pull them ahead" in that direction. Just like you can't dangle something on a string down through a cutting spinning blade.

In other words, the present isn't only decided by what happened in the past, but also by what will happen in the future.

 

That question is kind of irrelevant to whether a time machine could be built.

What I mean is, suppose I took you back in time in a time machine. We might even be able to see the past.
But you would still claim that we had actually not gone back in time, that we had never moved through time, and that the "us" who were watching what we were watching were not the same "us" who we seem to remember being in the future.

If, on the other hand, you mean that the past and future do not literally exist, that if we were somehow able to go forward in time (faster than the normal rate of time) we would find nothing, because it does not exist yet, that is a different issue.