"Why is there something instead of nothing"
Since there are two threads with the same title I guess my answer works for both of them...

This is the central theme of Heidegger's Introduction to Metaphysics :"Why are there beings at all instead of nothing" (p. 215)

What he does is essentially recast and reconceptualize the understanding of the nature of Being in a way that encompasses the concept of nothing. One of his most interesting conclusions is:
The concept of being that has been accepted up to now does not suffice to name everything that "is". (p. 218)

I recommend this, it's a good read, extremely dense but fairly short. As the "successor to Being and Time" alone it is worth consideration.

Which sounds like Luke is asking not about an empty world, but about there being no world ("a non-existent world"). Maybe he is confusing the two? — Pfhorrest

As I understand it, modal realists consider what is possible (i.e. possible worlds) to be actual, unlike actualists who draw a distinction between what is actual and what is possible.

For modal realists, what is possible necessarily exists (as possible worlds).
For actualists, what is possible does not necessarily exist (and only what is actual exists).

This is why modal realists cannot admit the existence of nothing ("no world"): because the existence of something is possible, i.e. because possible worlds necessarily exist.

But for actualists, what is possible does not equate to what is actual (possible worlds are not actual), so the existence of nothing ("no world") is merely possible without being actual. For the actualist it is not logically impossible that nothing might exist, whereas for the modal realist it is logically impossible that nothing might exist.

As for your own version of modal realism where "actual" is indexical, presumably this means that the "actual" world is the one in which one (currently) resides/inhabits. This seems to imply that a possible world requires someone to inhabit it in order for it to be "actual". If so, then how can there actually be an empty possible world? Moreover, can there exist an actual possible world without inhabitants?

... it is not logically impossible that nothing might exist ... — Luke

In so far as "nothing" denotes not-exist, your statement is doubly self-contradictory.

In so far as "nothing" denotes not-exist, your statement is doubly self-contradictory. — 180 Proof

I admit it was very poorly written, but where’s the contradiction?

To clarify, it is logically possible (for an actualist) that there could exist nothing or “no world”.

I highly appreciate the explanations. Thank you.

So if I understand correctly, then a modal realist way of thinking is like imagining the universe to be infinite where there is many versions of the world by sheer chance. And depending on the area of the universe, laws can change so that gravity falls upwards, for example. So in that universe, there are many worlds you might call a possible, real version of the world, but none of them would be "nothing" and be a world at the same time.

As I understand it, modal realists consider what is possible (i.e. possible worlds) to be actual — Luke

As for your own version of modal realism where "actual" is indexical — Luke

The usual (Lewis) form of modal realism also takes "actual" to be indexical, and so in those terms would not say that everything possible is actual. I agree with that too, but it's not peculiar to me. (). The modal realist says that other possible worlds exist in the same way that the actual world exists, but not that they are actual, in the same way that an eternalist says that other times besides the present exist as much as the present does, but not that they are present.

For the actualist it is not logically impossible that nothing might exist, whereas for the modal realist it is logically impossible that nothing might exist. — Luke

Both an actualist and a modal realist can use the language of possible worlds the same, they just take it to mean different things ontologically speaking. In that language of possible worlds, under either interpretation, it makes no logical sense to say "there's a possible world where there is no world". So in either case, it's not logically possible that there be no world at all.

However it is logically possible, in either case, for there to be a world in which there is nothing, i.e. an empty world, as Banno pointed out.

If we're asking why that possible world isn't actual, then the modal realist and the actualist diverge on their lines of argument. For the actualist, that's equivalent to asking "why doesn't that empty world exist instead of this one?" For the modal realist, there's no "instead of": both exist the same way, and countless others; the question is just why are we in this one and not that one; and the answer to that is that a world with us in it is by definition not empty.

where "actual" is indexical, presumably this means that the "actual" world is the one in which one (currently) resides/inhabits. This seems to imply that a possible world requires someone to inhabit it in order for it to be "actual". If so, then how can there actually be an empty possible world? Moreover, can there exist an actual possible world without inhabitants? — Luke

See above for clarification about other possible worlds not being "actual" (to us), but also for further clarification: on an eternalist view, "now" is just the time that we exist at. Does that mean that there could never be or have been times without people living in them to call them "now"? No. On an eternalist view, where "now" and "present" are indexical (it's just the time we're at, not ontologically special), that doesn't mean that times without inhabitants don't exist. Just that they aren't anybody's "now", because there's nobody there then to call it "now".

a modal realist way of thinking is like imagining the universe to be infinite where there is many versions of world — FlaccidDoor

So long as it's clear that "world" means something like "universe", and not "planet" like Earth, so we're not talking about somewhere far away in space there being another planet where things fall up, but about an alternate "universe" in a "multiverse" where things are that way.

... there could exist nothing ... — Luke

Not a contradiction? Or, at least, a reification fallacy?

:up: Your patience is much appreciated.

Not a contradiction? Or, at least, a reification fallacy? — 180 Proof

If the (i.e. our, this) universe ceased to exist, then nothing would exist. In other words, there would be “no world”, as it has been otherwise expressed here. Do you think that this cannot be expressed without contradiction?

Given an empty world, it stands to reason that for the world to be empty, a lack of existence needs to exist. A lack of existence in this case seems synonymous with empty space. So that begs the question: is space something or nothing?

If it is, then it seems like a world with nothing is impossible without differentiating empty from nothing, unless a world can exist without the dimension of space.

The modal realist says that other possible worlds exist in the same way that the actual world exists, but not that they are actual, — Pfhorrest

If "possible worlds" is just another name for "possibilities", then it seems uncontroversial that modal realists and actualists alike believe in the existence of possibilities.

The difference seems to be that modal realists consider those possibilities to be actualised (as other possible worlds), whereas actualists considers those possibilities to be unactualised (except in this world).

Both an actualist and a modal realist can use the language of possible worlds the same, they just take it to mean different things ontologically speaking. — Pfhorrest

Isn't the difference that an actualist considers what exists in this world to be all of the (i.e. the only) actualised possibilities, whereas a modal realist considers what exists in all possible worlds to be all of the actualised possibilities? Otherwise, what is the ontological difference between them? As you said, according to the modal realist, our world and other possible worlds "both exist the same way".

In that language of possible worlds, under either interpretation, it makes no logical sense to say "there's a possible world where there is no world". So in either case, it's not logically possible that there be no world at all. — Pfhorrest

This highlights the difference between actualists and modal realists, since modal realists view the possibilities (aka possible worlds) as already actualised, whereas actualists view the possibilities as what could become actualised, or how things might otherwise be in this world. Possible worlds are unactualised, unrealised possibilities for the actualist, who can conceive of the possible non-existence of this one and only world. For the actualist, there is no difference between "no world" and an empty possible world, because that possibility can exist only for this world, and that possibility has not yet been (or is not presently) actualised.

I have heard theories questioning whether "nothing" can exist or whether there can be an empty world. Maybe an empty world can exist. One thing I know is that at least one world (universe) exists. The causal chain that led to my existence is easy enough to scientifically trace, but only to a certain point. Science tells me it all started with a big bang; and religion tells me God willed it. But that doesn't really answer the question. I'm still wondering what caused the big bang or what caused God.

When I start thinking about it like that I obviously wind up in an infinite causal regression. But if there is an infinite causal regression, then there is no initial cause. On the other hand, if there isn't an infinite causal regression, then there is an initial cause that was not caused by anything- a spontaneous existence. Either way, this ancient philosophical question seems to be resolved- Existence is a fact for which there isn't cause.

If "possible worlds" is just another name for "possibilities", then it seems uncontroversial that modal realists and actualists alike believe in the existence of possibilities.

The difference seems to be that modal realists consider those possibilities to be actualised (as other possible worlds), whereas actualists considers those possibilities to be unactualised (except in this world). — Luke

If you substituted something like "realized" for "actualized" in there, that would be fine. The actualist believes that talk of "possible worlds" is just a figurative way of talking about states of affairs that could (possibly) be real but aren't; only the way things actually are is real, so "actual" and "real" are basically synonymous to them. But the modal realist believes instead that all possible states of affairs are equally real, each a different world, and what makes one state of affairs actual and the others merely possible is that one of them is the way things are in the world we're a part of, and the others aren't.

I keep using this analogy with philosophy of time because it really seems to clarify things. Both a presentist and an eternalist will talk about the past and the future the same. But the presentist considers "the past" to be merely a state of affairs that was once real but is no longer, and the future a state of affairs that has yet to become real but might; while an eternalist considers past, present, and future to be all equally real, and "the present" to just be the time that we happen to be at.

The presentist is like the actualist, while the eternalist is like the modal realist, just regarding time instead of possible worlds. (And I, uniquely so far as I'm aware, collapse those to the same problem, and consider other times to just be a subset of possible worlds, so the world with nothing in it but shrimp is just as real as last year: neither is actual, or present, but both are ways-things-could-be, equally real as the way things actually, presently are, just not the way things are for us, now).

The presentist is like the actualist, while the eternalist is like the modal realist, just regarding time instead of possible worlds. — Pfhorrest

Yes, I get the analogy. The actual world is the one we inhabit, and all the possible worlds which exclude us cannot be realised for us. But, as with the static world of eternalism, it is not as though we could ever "switch" from one possible world to another, or change, anyway. The fix is in, and all possibilities are already realised. But I digress...

Does this mean you concede that it does make logical sense for an actualist to say "there's a possible world where there is no world"?

My 2 bit(coin)s –

Actualism: every possible chess match constitutes chess itself.

Possibilism (i.e. modal realism): every possible ruleset of every possible game is a distinct counterpart of the ruleset of chess.

Actualism: the territory consists of – affords – every possible map of the territory.

Possibilism (i.e. modal realism): every merely possible territory is a counterpart of (this) actual possible territory.

Actualism: every possible world is a version – configuration – of the actual world.

Possibilism: every merely possible world is a counterpart of (this) actual possible world.

Is there any possible version of the actual world that is 'the negation of the actual world' (i.e. nothingness)?

Is there any possible world in which it is true that 'a possible world is not a possible world' (i.e. nothingness)?

but none of them would be "nothing" and be a world at the same time. — FlaccidDoor

That's how I see it.

Does this mean you concede that it does make logical sense for an actualist to say "there's a possible world where there is no world"? — Luke

Nope, because that's like saying "before there was time...".

You could talk about a time in which nothing existed though, or a possible world in which nothing exists. But that's still a time, or a possible world, respectively.

Does this mean you concede that it does make logical sense for an actualist to say "there's a possible world where there is no world"?
— Luke

Nope, because that's like saying "before there was time...".

You could talk about a time in which nothing existed though, or a possible world in which nothing exists. But that's still a time, or a possible world, respectively. — Pfhorrest

Tu quoque???

Nope, because that's like saying "before there was time...". — Pfhorrest

I don't think that's analogous.

The realised empty possible world of the modal realist is equivalent to the actualist's unrealised possibility that this world could cease to exist.

You could talk about a time in which nothing existed though, or a possible world in which nothing exists. But that's still a time, or a possible world, respectively. — Pfhorrest

There is no realised and pre-existing possible world for the actualist like there is for the modal realist. No other worlds exist for the actualist but this one. A "possible world" for the actualist is just an unrealised possibility of this world. That's why it makes logical sense for the actualist to say "there's a possible world where there is no world". It's not some other world; it would be this one, if the possibility of this world's extincton were to be realised.

Empty in not containing any individuals - hence Noether's Theorem could not be proved. — Banno

WHAT is empty?

Do you think it makes sense for a presentist to talk about a time before time, since to her no other times besides the present are real, they're just ways that the present has been or will be? A time before anything existed, sure... but not a time at which it was not any time.

How is that analogous? The possibility (now) of there coming to be no possibilities (at some future time) is not illogical.

The possibility (now) of there coming to be no possibilities (at some future time) is not illogical. — Luke

What is (logically) possible or impossible is knowable a priori. Since something does exist now, it is clearly possible that something exists. If there could come to be a state where nothing exists, it would still remain (logically) possible for something to exist -- that possibility would have once been actual, back in the past that is our present, even if it's not longer actual in some annihilated future.

It may be a possibility for the actual world to become empty, devoid of things. But that possibility is still the possibility of an empty world, not of some kind of non-world.

If there could come to be a state where nothing exists, it would still remain (logically) possible for something to exist — Pfhorrest

I’m not saying it’s impossible that something exists - that would be absurd. Im saying it’s possible that nothing could exist, or that there could be “no world”.

It may be a possibility for the actual world to become empty, devoid of things. But that possibility is still the possibility of an empty world, not of some kind of non-world. — Pfhorrest

There is only one world for the actualist: this one. The realisation of the possible annihilation of this world would make it a non-world. It would remain logically possible for this world to exist again after its annihilation, but it would also remain logically possible for this world not to exist again after its annihilation; to remain a non-world.

I’m not saying it’s impossible that something exists — Luke

You said "The possibility (now) of there coming to be no possibilities (at some future time)". If there are no possibilities, then there is no possibility of something existing -- it is impossible for something to exist. If that was just misspeaking on your part, then nevermind.

The realisation of the possible annihilation of this world would make it a non-world — Luke

That is the thing in question. We could annihilate everything in this world, and make it an empty would, but would it then be no world? I say no, and not for any reasons dependent on modal realism. Even if there's only the actual world, if everything in it were annihilated it would remain a world, just an empty one. Just like, if there comes to be some time in the future where nothing exists anymore, that wouldn't be not a time.

You said "The possibility (now) of there coming to be no possibilities (at some future time)". If there are no possibilities, then there is no possibility of something existing -- it is impossible for something to exist. If that was just misspeaking on your part, then nevermind. — Pfhorrest

If this world were annihilated, then there would be no possibilities. I probably should not have said in my last post: "It would remain logically possible for this world to exist again after its annihilation," I was just trying to be even-handed, but I actually don't see how this could be possible. It is possible there could be a big crunch where even the singularity gets annihilated. It's hard to see how there could be any possibilities left in that scenario, or anything left to call a "world".

If this world were annihilated, then there would be no possibilities. — Luke

It sounds like you're not talking about logical possibility, which could be a source of our problem here.

If something is logically possible then it's logically possible always and forever. That's why I said earlier "What is (logically) possible or impossible is knowable a priori." It's not contingent on any particulars of the world. So, since it is clearly logically possible for something to exist, because something does actually exist, then even in a future state of this world where everything is annihilated, it is still logically possible for something to exist. That doesn't mean it's possible in any other sense, like physically or technologically or anything like that.

...even in a future state of this world where everything is annihilated, it is still logically possible for something to exist. — Pfhorrest

What “world” would remain for something to exist in? It’s not that everything in this world would be annihilated, but the world itself.

Why is it logically impossible for a world to be permanently annihilated?

You guys do understand that possible worlds are just made-up, don't you? It's all a word game.

What “world” would remain for something to exist in? It’s not that everything in this world would be annihilated, but the world itself. — Luke

A "world" is just some state of affairs, whether you're a modal realist or an actualist. If there is some state of affairs in which nothing exists, that is still some state of affairs.

In any case, you're missing the point about logical possibility. Even if "the world" was annihilated, it would remain logically possible for "a world" to exist, because "a world" actually exists now, which means it's logically possible now, and logical possibility doesn't change over time, so it remains logically possible always.

A "world" is just some state of affairs, whether you're a modal realist or an actualist — Pfhorrest

I don’t think so. It’s not “a world” for the actualist, because there isn’t more than one; there’s only this actual world.