The minimal universe

Great Debates
1

So this post is necessarily going to be a bit abstract, speculative & vague but I’m hoping it’ll move to somewhere productive. It also has a lot of both physics & philosophy in it.

Imagine the set of all possible universes. In some universes, Hitler will have won WWII, in others, gravity will be 9.3 m/s instead of 9.81 etc.

Now, my question is, of the set of possible universes, what would constitute the most “minimal” universe in the set. In other words, how much of our universe can we strip away and still have it be a universe.

So let’s get the easy stuff out of the way first, we can obviously strip away all matter and imagine a matterless universe.

What about dimensions? It seems like reducing down from 3 dimensions to 0 dimension universe is going to be easy. But can we remove dimensions all together?

Does the idea of space still make sense in a matterless universe? In this case, is it possible to strip away space completely or is the best we can do is to make space a single point?

Can we strip away the concept of quarks? Even though there are no quarks in our universe anymore, there’s still the idea of quarks, the potential for quarks to form. Can we remove that also from our universe?

What about the 4 forces: gravity, electromagnetism, weak & strong nuclear force? Can we strip those away without doing damage?

What about distance, the concept of distance. Actual distance itself is useless in a universe with no space but that doesn’t mean that we still can’t reason about distance, is that something you can remove from a universe?

What about geometry itself? Can we actually remove geometry from the universe? Can we make pi not be 3.1415… and the internal angles of a triangle not add up to 180 degrees on a euclidean plane?

And the ultimate, in my mind, could we strip out tautologies? Could we have a universe in which “A is A” is an optional, bolt on extra?

In my mind, somewhere as you go down that chain of more and more fundamental things, you reach a point where you can’t remove those things from a universe anymore. However, all of this is gut intuition and I’m not really sure how correct my reasoning is.

To me, the most fascinating dichotomy is between removing the thing and removing the concept of the thing. We can reason about 4 dimensional universes even though no such thing exists in our experience because there exists the concept of a 4 dimensional universe. That concept would still exist even if there was nothing sentient to grasp it. removing dimensions is easier than removing dimensionality.

So I’m wondering, pushing this thought experiment, just what do you conceive as the most minimal possible universe?

2

Actually, Shalmanese, you’re just (self) indulging in what philosophers have done for centuries: positing conceivable worlds. Thee are even philosophers who have suggested that, because they are conceivable, such worlds must really exist!

My problem with these kinds of thought experiment is that I struggle to conceive of things which just don’t make sense to me, such as Beings that are more Supreme because they exist rather than not, or zombies who can share their experiences despite never having had any.

For example, you say you can conceive of a zero-dimensional universe and an absence of fundamental forces. When I try this, I get an ERROR: DOES NOT COMPUTE. Strangely, when I imagine mucking around with pi or considering A=-A not to be absurd, I just imagine a slightly broken calculator which just displays answers which disagree with other calculators whose answers are more ‘useful’.

I suspect we all have personal barriers to what we can really, I mean really really, conceive. My powers of conception are anything but Immaculate.

3

That isn’t a universe, it’s a nothing.

4

Take a look into Victor Stenger, The Comprehensible Cosmos. He argues that the physical laws of the universe are basically consequences of it being as “minimalist” as possible. That is, the physics of the universe come from the fact that all points of view (reference frames) are equally valid.

Maybe there could be a universe with fewer dimensions, almost surely there could be a universe with less matter. Mathematical concepts are consequences of our axioms, so we’re pretty much stuck with them.

5

Is this even supposed to make sense? A ‘concept’ of a thing (or our concept, to be precise) only exists in a universe where 1. the thing exists and 2. a mind exists to conceptualize that thing. So either the conditions are met, or they aren’t, but there is no fundamental dichotomy of the sort you’re referring to.

:rolleyes:

6

There are no forces without matter. No mass means no gravity. No electrons means no electromagnestism. No subatomic particles means no strong or weak force. You are left with a vacuum state where for all intents and purposes there is no time or distance. Concepts like pi or geometry or gravitational constants are meaningless because they are just tools for describing the universe.

7

Bwa? I have a concept of a unicorn, yet I’m pretty sure it doesn’t actually exist.

8

Oops, sorry, that’s an embarrassing oversight. What I was getting at was the absurdity of imagining a universe devoid of anything, and then wondering: “Can we strip away the concept of quarks? Even though there are no quarks in our universe anymore, there’s still the idea of quarks, the potential for quarks to form.” The concept of quarks only exists in our universe, which has the right conditions for human minds to exist and conceive such things. And I don’t even know what is meant by “the idea of quarks, the potential for quarks to form”.

9

It seems to me all you need to qualify as a universe is information. Any set of data for which some question could be true or false is a universe. A .jpg file is a universe of sorts, but a static one. Universes become more interesting if they have time. Any computer simulation could be considered a universe with a time dimension. Universes we would consider interesting would have to be complicated enough to construct intelligent beings, and these would have to be pretty complex, like ours. I’m curious whether intelligence would be possible in universes simpler than ours.

10

Ooh, I completely forgot about time! Can we remove time from a universe?

Let me pose a thought experiment. Assume you have a universe with zero particles in it, does gravity exist? Now, say you took that universe and added one particle, is there now gravity in that universe? A particle can’t act on itself so there’s no actual gravitational force. What if we then add another particle? Is it the second particle that creates gravity? If you accept that it’s possible to have universes with different gravitational constants, what determines the gravitational constant? Is it possible to have a matterless universe in which, if you were to add 2 particles, G would be 3 and another matterless universe in which, if you were to add 2 particles, G would be 4? If so, are these two matterless universes the same thing or different things?

Also, is there a difference between a universe in which G has a value of 0 and a universe in which the concept of gravity does not exist? If so, what is that difference, if not, why not?

11

I had a big long complicated discussion about this with another friend of mine and my position was that information, no matter how intricately it is arranged, must necessarily be meaningless without a schema, a way of interpreting that information and this means that information cannot be a universe.

No matter how you arrange bits, those bits won’t do anything unless something outside of those bits is there to interpret it. This is the point where my head started hurting because I couldn’t figure out what it was that’s “running” the universe.

12

In our current universe, by our current laws of geometry, it is impossible to form a triangle with side lengths 1, 1 & 3 (assuming euclidian plane, straight lines blah blah). I would argue that our universe does not contain the concept of a 1, 1, 3 triangle.

Now speculatively, if we could imagine universes in which geometry itself was different, there could conceivably be a universe in which a 1, 1, 3 triangle makes perfect, mundane sense. It’s a bit of a stretch but just go with me here.

Now, my question is, is a universe which is particle for particle, identical to us and contains no actual 1, 1, 3 triangles but which the potential for making 1, 1, 3 triangles is present a different universe from the one that we currently inhabit?

13

There are no quarks anymore?

14

The most minimal universe that’s ever been discussed scientifically is, to my knowledge, the de Sitter cosmology, which contains no matter at all, and no forces other than a particular variant of gravity (the cosmological constant). In our own Universe, the cosmological constant is generally interpreted as a sort of “matter” (using the term loosely) called the cosmological constant, but that interpretation doesn’t really work in the de Sitter model. As it’s usually formulated, normal gravity like we’re familiar with (which requires matter to act as a source) still exists in the equations governing de Sitter space, though without any actual matter in the space, it’s rather irrelevant, and could be easily enough removed.

Of course, de Sitter space doesn’t describe the real Universe that we actually live in, since ours does contain matter. But it’s useful as a toy model to help understand more complicated universes, and is the basis for other models (like Hoyle’s steady state model) which did hope to describe the real Universe.

15

From your link:

Any thoughts about this unsourced speculation?

16

Not since DS9 got cancelled.