I'm not a physicist nor a physics student. Sorry if I'm writing nonsense.

I'd like to understand how physicists can go on elaborating more and more theories, while the bigger problems have remained unsolved for centuries (afaik).

For example, Zeno's paradoxes. So which is it? Is time infinitely divisible or not? Is space infinitely divisible or not? How can things move?

Why is it said that time is a "dimension"? The way I see it, it's just an illusion created by the motion of all things that exist.

My favorite one: does void exist? If not, what are we really doing when we suck the air out of a sealed container? But if void does exist, how come particles keep popping up in the void (according to quantum physics, right?)?

Anyway, I'm putting my flame suit on.

Ambitwistor

I'd like to understand how physicists can go on elaborating more and more theories, while the bigger problems have remained unsolved for centuries (afaik).

That really depends on your opinion as to what the "bigger problems" are. There's only so much point in arguing about philosophy.

Zeno's paradox was resolved with the invention of calculus.

So which is it? Is time infinitely divisible or not? Is space infinitely divisible or not?

We don't know, but there's no paradox either way.

Why is it said that time is a "dimension"?

In order to specify the state of a particle, you have to give not only its location, but the time at which it is at that location. Time is a dimension even in Newtonian physics. In relativity, Einstein found that time was not only a dimension, but it was unified with the space dimensions: two events that are at different locations in space but occur at the same time according to one observer, occur at different locations in space and at different times according to another observer. Shifting reference frames mixes the time and space separations.

The way I see it, it's just an illusion created by the motion of all things that exist.

It's kind of pointless arguing over whether time is "real" or "an illusion". What matters in physics is, we can measure something with clocks, and we call that time.

My favorite one: does void exist? If not, what are we really doing when we suck the air out of a sealed container?

We never make a perfect vacuum when we suck the air out; there is always some left over.

But if void does exist, how come particles keep popping up in the void (according to quantum physics, right?)?

It's just a matter of what you choose to mean by the word "void". Again, this is a question of philosophy, not physics.

Staff Emeritus
Gold Member

Originally posted by druk
I'm not a physicist nor a physics student. Sorry if I'm writing nonsense.
Welcome to physicsforums.
I'd like to understand how physicists can go on elaborating more and more theories, while the bigger problems have remained unsolved for centuries (afaik).
Simple. We don't. We solve the most trivial problems first.
For example, Zeno's paradoxes. So which is it? Is time infinitely divisible or not? Is space infinitely divisible or not? How can things move?
Zeno's paradox was solved by the discovery of calculus some four hundred years ago. Simply put, an infinite series does not necessarily have an infinite sum.
Why is it said that time is a "dimension"? The way I see it, it's just an illusion created by the motion of all things that exist.
Time is a dimension because "meet me at the pizza parlor at 3 pm" and "meet me at the pizza parlor at 3 am" are two distinctly different locations in "spacetime." It doesn't suffice to provide just the location ("the pizza parlor") -- you have to provide another coordinate, time, to fully specify the meeting -- and that is the very definition of a dimension.
My favorite one: does void exist? If not, what are we really doing when we suck the air out of a sealed container? But if void does exist, how come particles keep popping up in the void (according to quantum physics, right?)?
Depends on what you want 'void' to mean. Physics supposes there is such a thing as a vacuum, which is the lowest energy state possible. It is defined to be 'vacuum' simply by virtue of its lowest possible energy. Calling it 'vacuum' does not mean it is really empty -- it can be seething with virtual particles. A better term than 'vacuum' would be 'lowest energy configuration.' The terms mean exactly the same thing to a physicist. While the popular idea is that 'vacuum' means being completely devoid of all particles, a physicist just thinks of the vacuum as the lowest energy configuration, which isn't necessarily completely devoid of particles.

- Warren

Staff Emeritus
Gold Member
Arrrrrgh you did it again Ambi.

- Warren

Simple. We don't. We solve the most trivial problems first.
OK, it's nice that we all agree, then.
Zeno's paradox was solved by the discovery of calculus some four hundred years ago. Simply put, an infinite series does not necessarily have an infinite sum.
I've read something about that, but I really don't buy it. Calculus (and mathematics, for that matter) is just a very complex tautology, so it doesn't really add to the solution, I think. Of course language is a very complex tautology, too. I may be wrong, though.
Time is a dimension because "meet me at the pizza parlor at 3 pm" and "meet me at the pizza parlor at 3 am" are two distinctly different locations in "spacetime." It doesn't suffice to provide just the location ("the pizza parlor") -- you have to provide another coordinate, time, to fully specify the meeting -- and that is the very definition of a dimension.
You have a point, but it seems odd that the pizza parlor can exist without time, but time cannot exist without the pizza parlor, because it's the pizza parlor's motion (the universe's motion) that creates time.
Depends on what you want 'void' to mean. Physics supposes there is such a thing as a vacuum, which is the lowest energy state possible. It is defined to be 'vacuum' simply by virtue of its lowest possible energy. Calling it 'vacuum' does not mean it is really empty -- it can be seething with virtual particles. A better term than 'vacuum' would be 'lowest energy configuration.' The terms mean exactly the same thing to a physicist. While the popular idea is that 'vacuum' means being completely devoid of all particles, a physicist just thinks of the vacuum as the lowest energy configuration, which isn't necessarily completely devoid of particles.
So, actual vacuum doesn't exist, because the energy level can never reach zero.But what would you say that there is between one particle and the one immediately next to it? At some point they are not making contact (otherwise they would be moving in the same direction at the same speed forever), so if vacuum doesn't exist, that space must be filled with something. Not energy, because energy means actual particles (or not?). Another particle then? But then, this would mean that a particle only can move when another particle is willing to take its place. Is that so?

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Originally posted by druk
Calculus (and mathematics, for that matter) is just a very complex tautology
It sounds to me like you don't know much math. Let me guess -- math is hard, so you just threw up your hands and gave up, right? I imagine that you just declared that it's needless repetition to rationalize the fact that you consciously chose to stop studying it because you found it so difficult. Tragic.
You have a point, but it seems odd that the pizza parlor can exist without time, but time cannot exist without the pizza parlor, because it's the pizza parlor's motion (the universe's motion) that creates time.
It is meaningless to speculate whether or not something can exist without time, because neither you nor I have ever seen a universe without. And besides, exactly how can the entire universe have motion? What could you use to measure the universe's motion? What standard would you measure this motion against? This sounds like gibberish to me.
So, actual vacuum doesn't exist, because the energy level can never reach zero.
What a physicist would call a 'vacuum' certainly exists. What a layman calls a 'vacuum' does not exist.
But what would you say that there is between one particle and the one immediately next to it?
It might be a void with absolutely no particles. There is a non-zero probability, however, that the space will not be totally empty.

- Warren

Homework Helper

Originally posted by druk

I may be wrong, though.

Congratulations, you too can now be a scientist!

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I have an idea - https://www.physicsforums.com/forumdisplay.php?s=&daysprune=&forumid=112

Nautica

Mentor

Originally posted by druk
You have a point, but it seems odd that the pizza parlor can exist without time, but time cannot exist without the pizza parlor, because it's the pizza parlor's motion (the universe's motion) that creates time.
The pizza parlor does not exist without time since it is possible to specify a time at which the pizza parlor does not exist. So specifying "the pizza parlor" does provide a hint as to the time: you can safely assume that the time someone plans to meet you will be one at which the pizza parlor exists. Its just that its not accurate enough to actually meet without a specific time.
It sounds to me like you don't know much math.
I don't like math either. Its a royal pain in the ass. But druk, its an essential tool without which it would not be possible to describe (much less predict) anything quantatative about how the universe works.

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