What does "space" consist of?

[Agen]

This is hard to explain, but it has been bugging me for quite some time. Is there a limit to where and object can exist or there is no limit, meaning you can calculate the position of an object forever and get an unlimited amount of digits? What I mean is does space consist of some points where the smallest possible objects can exsist (the smallest space possible) and an object cant exsist in between there points?

[ronthepon]

Good question. It's been bugging me as well.

 

Rotational motion will be facing problems if it is so.

[InfiniteNow]

You might find some clarification (however, not likely an exact answer) by studying Planck lengths and Planck time...

 

http://en.wikipedia.org/wiki/Planck_length

 

http://en.wikipedia.org/wiki/Planck_time

[Qfwfq]

Although often taken to mean a discreteness of space, the Planck length is simply a scale under which the laws of physics aren't expected to be the same as above it. I fully agree with Ron:

Rotational motion will be facing problems if it is so.

and the same for the Lorentz group. Good thinking, Ron! :doh:

[Nootropic]

The elusive vacuum energy, anyone?

[InfiniteNow]

Check out Cassimir effect.

[Jay-qu]

what about it? even if it did exsist, we are going to have a hard time finding out how to use it!

[Alon]

what about it? even if it did exsist, we are going to have a hard time finding out how to use it!

it's not a matter of if it exists, it does, as infinitenow mentioned casimir effect is an evidence of it.

 

anyway, i think that space doesnt consist of a particular matter or ideal points, it's merely a vaccum state.

in the atom, most of it compose of vaccum, which in it there are the nucleus and the electron.

[Tormod]

it's not a matter of if it exists, it does, as infinitenow mentioned casimir effect is an evidence of it.

 

No, an effect is not a proof of anything, it is merely an indication that something is being affected by something else.

[TheFaithfulStone]

I took that to mean "Yes the Casimir effect does exist."

 

So here's the big question - is space time quantized?

 

What does it mean if the answer is yes? What does it mean if the answer is no?

 

Why does it spell trouble for rotational motion?

 

TFS

[Alon]

No, an effect is not a proof of anything, it is merely an indication that something is being affected by something else.

but the casimir effect is an indication of some sort of vaccum energy, is it not?

[Qfwfq]

Yes, I agree that the Casimir effect is a consequence of vacuum fluctuations.

 

So here's the big question - is space time quantized?

 

What does it mean if the answer is yes? What does it mean if the answer is no?

 

Why does it spell trouble for rotational motion?

The answer is no and it would mean a great difficulty with isotropy of space, as well as with Lorentz boosts.

 

Which direction would the unit movement be in and according to which reference? If you allow them to be in any direction, you end up with the possibility of any displacement. In any case, if you allow rotation of a given angle [math]\alpha[/math] around a given point, this implies displacements of [math]\alpha r[/math] at each distance [math]r[/math].

[Tormod]

but the casimir effect is an indication of some sort of vaccum energy, is it not?

 

Possibly (even likely), but it is not proof of it. Just nitpicking on my behalf.

[UKOK]

I signed up to this forum last night because I was googling the plank length because I was trying to get my head around exactly this discussion.

 

I am glad someone earlier correct the view that plank length is the smallest possible distance. If this were the case then we could argue that space is made up from discrete chunks. I had problems with this but my conclusions are far from lucid at the moment. This all started from a different question for me. Why is the speed of light what it is and why a maxima? what other limitations were there around both distance and time.

 

My worry is that if the smallest distance is x then motion is also constrained to move in chunks because something cannot move a distance smaller than x.

 

For example, imagine the edge of a golf ball travelling through space at 100,000 miles an hour. If it is unable to move less than the plank length then how does it jump the 'gap'. If point A and point B are plank distance apart then it needs to be at point A at time X and point B at time Y where time Y is the time it takes to move plank distance at 100,000 miles per hour (lest call it Z).

 

But what happend in between as the edge of the ball cannot be in between those two positions as it would mean moving a distance smaller than plank. The alternative is that the ball sits at point A for the period Z and then instantaneously appears at point B.

 

This says to me that things move around by being stationary at points and then moving plank distance instantaneously where the interval of the jumps is dictated by the speed (i.e. how long it remains stationary). This raises too many questions if this were to be the case and so I believe that space time is continuous. I.e. it can be infinitely divided and still end up with spacetime.

[IDMclean]

This all started from a different question for me. Why is the speed of light what it is and why a maxima? what other limitations were there around both distance and time.

 

Just a slight correction. c is invariant to in reference to frames. Not maximal.

 

This subject is talked about in a paper that I have read to some extent, though my understanding is far from complete. Suffice it to say that they talk about much of what is being currently discussed.

 

Faster-than-c signals, special relativity, and causality. It is mainly concerned with casimir vacuums, and faster than c propagation speeds of light in different vacuum expectations.

[CraigD]

My worry is that if the smallest distance is x then motion is also constrained to move in chunks because something cannot move a distance smaller than x.

…

This says to me that things move around by being stationary at points and then moving plank distance instantaneously where the interval of the jumps is dictated by the speed (i.e. how long it remains stationary). This raises too many questions if this were to be the case and so I believe that space time is continuous. I.e. it can be infinitely divided and still end up with spacetime.

My understanding is that best current theory predicts that space is continuous in the way UKOK describes.

 

The Planck length, mass, and time units exist mostly for convenience in working with physics – their use eliminates a lot of inconvenient constants appearing in equations. The view that space and time are, in a counterintuitive way, “quantatized” into distinct chunks is, I think, due to the uncertainty principle, which predicts that it’s impossible to predict the position at a precise time of body of a specifically known mass and velocity more precisely than to within a specific volume of space. What the body is “really” doing on a scale finer than can be observed is … unobservable. To ease our understanding, there’s nothing wrong with imagining it to be moving in the way we perceive everyday objects to, so long as we understand that we can never actually observe this. Though quantum theory forbids bodies in certain situations from being observed in certain regions (eg: electrons in “forbidden” shells around an atomic nucleus), these regions are positioned in a smooth, continuous way in space, so quantum theory doesn’t imply a fixed quantatization of space.

 

Several theories about the ultimate nature of reality include a feature commonly called the holographic principle, which leads to the conclusion that all of reality can be represented as a large single integer. If this is true (the proving or disproving of which, if successful at all, is likely to be the work of generations of theorists), then OKOK's worry that space is ultimately “chunky”, or “granular”, is founded. However, to fit current observed data, the granule size predicted by these theories is many times smaller than the Planck length.

[Farsight]

This is just opinion, I can't justify it or prove it at this moment in time, but:

 

I think space is smooth and continuous. But the things in it and the things that act upon them, are not. The analogy is your display screen. It's the pixels and the mouse pointing that are discrete. Not the expanse of screen.