Small

[Gingerbaker]

As everything beyond our universe is infinitely large, does that mean also that things can be infinitely small. So you could have an infinite amount of small universes inside one of our known atoms…quarks…smaller and smaller…smaller…..?

[ToraToraTora]

spacenoob: "Is space, like, split up into tiny cubes?" In a manner of speaking, yes.
The Planck length is space time quantized, the minimum unit first theorised by Max Planck the legendary physicist. Think of it like money, a pound is made up of 100 pence, now imagine 1p is the smallest possible unit, in physics that's the Planck length. My link above covers it.

[davebro]

so - string theory or loop quantum gravity ?

[jim360]

Perhaps you should read your link again, TTT:

// it has been conjectured that ... the familiar notion of distance [is] inapplicable below the Planck length. It is *possible* that the Planck length is the shortest *physically measurable* distance ... [emphasis added] //

So you're misunderstood two things: firstly, we don't yet know whether the Planck length is physically meaningful, although it's likely to be, eg roughly it's the scale at which quantum gravity effects are significant. Secondly, even if it *is* meaningful then it's not in the literal sense of "nothing smaller exists", but rather "nothing we can do physically could measure anything smaller".

As a further point, the Planck length, as derived in the wiki link, is merely a way of combining physical constants to produce something that has dimensions of length.

Spacetime is almost certainly continuous, and it's at the very least wrong to say that we've established otherwise.

Hopefully that clears things up, ScienceNoob.

[THECORBYLOON]

Is there proof there is nothing shorter than the Planck length?

[ToraToraTora]

Jim, ok thanks for clarifying.

[ToraToraTora]

So jim would you say then that if the Planck length is (probably) the smallest measurable there are smaller immeasurable things? Can things therefore be infinitely small as suggested in the OP?

[ScienceNoob]

Thanks jim360! Although I think it would be cool if space was made up of tiny cubes!

[Old_Geezer]

ScienceNoob
IMO yes, everything comes in separate bits. But not being expert in such things I'll watch out for others posting reasoned arguments how it can possibly be otherwise. IMO even emergent time is a result of such a split, so it isn't just space. All conjecture at present though.

[jim360]

I'm not aware of anything stopping it. If nothing else, as I'm sure Naomi would point out, there's just a lot of stuff we just don't know :P

In this case for example, trying to work out what goes on at, or smaller than, the Planck Length, is *very* difficult. To probe it, you need to go to energy scales vastly beyond anything we're capable of, something like 10^16 times more energy than in the LHC for example. In terms of length scales, that's roughly the difference between the Milky Way and London.

There are certainly theories in which indeed the Planck length is the minimum meaningful distance scale -- loop quantum gravities, apparently. They aren't my field, so I wouldn't want to offer any firm opinions, beyond noting that they are still very much in the development stage.

[roadman]

Its all relative man

[douglas9401]

Is a Planck length equal to two short Plancks?

Asking for a corrected geezer.

[jno]

the answer's probably in the documentary film, douglas. Made some years ago by Eric Sykes as I recall.

[THECORBYLOON]

Since everything in the whole universe was created from nothing, followed by a massive expansion, that would suggest to me that at that point, there must have been an awful lot of something smaller than a Planck length.

[naomi24]

Jim, //If nothing else, as I'm sure Naomi would point out, there's just a lot of stuff we just don't know :P //

I guess that's a 'grin' at the end there but I don't understand why it's there. You are right - that is what I would say. Do you disagree with it?

[jim360]

Not exactly a disagreement, I just thought it was amusing that our positions, however briefly, overlapped. That said, I think we probably tend to mean different things by "we don't know", but that's a conversation for another time.

[naomi24]

Jim, How can 'we don't know' mean anything other than 'we don't know'?

[jim360]

It's what comes afterwards, ie for me it's more of a "we don't know, but we can still expect such-and-such...". I always got the sense, and in this I may be mistaken, that for you the sentence just ends as "We don't know."

[naomi24]

Jim, //I always got the sense, and in this I may be mistaken, that for you the sentence just ends as "We don't know."//

It does really. 'We can expect' often leads to disappointment so I tend not to depend upon conjecture.

[jim360]

It's not really a conjecture, exactly. For example, suppose you have created a theory that describes what might happen at very small scales. What happens when you take that theory and "zoom out"? The answer is that you should be able to describe what happens at large scales -- you can "recover" our current understanding of physics from this new theory.

This is how, for example, Einstein knew he'd got his equations for General Relativity correct: he could get Newtonian physics right. Likewise, in an early draft, that conceptually is the same as his actual paper in terms of what's going on, he got the equations "wrong", and knew they must be wrong because he wasn't getting Newtonian gravity out of it.

So it is in this case. We don't know what's going on at Planck scales, and indeed it may even be that nothing special happens there. But we *do* know, or at least we know to expect, that if you get the small-scale right, then it will be an extension of, rather than a replacement for, General Relativity. As a case on point, Loop Quantum Gravity, whatever the hell that is, seems to be running into this precise roadblock right now, ie we aren't getting out of it anything that matches our current understanding.

The point really is that the "...but we can still expect such-and-such" is that, in order to make progress, it's good to establish a sensible starting point. And a very sensible starting point is this idea that our current description, while surely incomplete, is correct as far as it goes. General Relativity is a good description of gravity, that has survived countless experimental checks, that only breaks down in extreme examples -- but in that case, you want to patch it, rather than tear it all up.

[naomi24]

But none of that is what we’re talking about, Jim. I mentioned multiple universes so I think it’s pretty safe to say ‘we don’t know’ and mean exactly that.