Finetuning the multiverse

It has occurred to me that there is a kind of fine-tuning of multiverse theories.

If there is too large a variety of universes within a multiverse, we get skeptical problems. For instance, if all possible laws of nature are realized, then induction-friendly laws like “Gravity is always attractive” are either outnumbered by or at least do not outnumber nasty laws like “Gravity is attractive until the end of March 2026 and repulsive afterwards”. Or if there are too many kinds of material arrangements, we would expect scenarios with local order, like Boltzmann brains to outnumber or at least not be outnumbered by scenarios like brains arising by evolution.

On the other hand, if there are too few universes, then the laws by which universes are generated need to be themselves fine-tuned or else there won’t be life.

So, a multiverse theory needs to be tuned as to the variety of universes it supposes. I don’t have a a great argument that this tuning is highly improbable, but it might be. My intuition says, for what it’s worth, that the on naturalism we should either expect a single universe or a very wide and varied multiverse, and the latter is likely to engender skepticism.

Skepticism and a causeless beginning to the universe

Suppose that the universe began with the Big Bang, and the Big Bang had no cause, so the universe came into existence ex nihilo. It then went through many (infinitely many if time is continuous) stages—the one-second-old universe, the ten-second-old universe, the five-minute-old universe, the one-year-old universe, the 7-million-year-old universe, before arriving at the present 13.7-billion-year-old universe, and then (presumably) going onward.

Question: Why did the universe start in the Big Bang state rather than in one of these many other states?

Assuming the universe has no cause, there does not seem to be any compelling reason to think the Big Bang state is somehow “more likely” as a starting state of the universe. (If anything, it seems a less likely state, because it has lower entropy than the later states.)

Now, granted, if the universe started in a sufficiently “late” (as compared to our state) stage, there would be no observers in that universe other than perhaps Boltzmann brains, due to the universe having expanded too much. So we have an interesting bit of fine-tuning: the universe started in a sufficiently early stage that there was still time for life.

Let’s ignore that otherwise intriguing observation, however, and push ahead. Let S_t be the t-units-of-time-past-Big-Bang stage of a universe like ours. And let’s ask:

• Conditioning on all our observations, and given that the universe has no cause, is it more likely that the universe starts with S₀ (i.e., starts with the Big Bang) than with, say, S_t1, where t₁ > 0?

If the answer is negative, then the supposition of a causeless universe leads to a skeptical hypothesis: we have no more reason to think the universe started with the Big Bang than that it started in the t₁ stage.

The answer may be positive in some cases. As we already saw, if t₁ is past the time of there being any observers—or just past the time of there being any observers making observations like ours—then we can be sure the universe didn’t start in S_t1.

If it turns out that evolutionary is logically necessary for consciousness, as some materialists think (because, basically, evolutionary history is necessary for defining proper function for making functionalism run), we might get a positive answer if t₁ is so close to the present that there was insufficient evolutionary history for our consciousness if the universe started at t₁.

But if t₁ is any time between 0 and about 3.7 billion years ago, our observations do not differentiate between the hypothesis that the universe started with S₀ or that it started with S_t1. Thus, the answer to the bulleted question above is negative. Moreover, it’s negative for each of the many t₁ in the relevant range (more than 0 but less than about 10 billion years). Thus, on a no-cause hypothesis we should not prefer the Big Bang hypothesis over a whole bunch of skeptical hypotheses holding that the universe started in a more developed form.

This argument will please theists who think the universe had a cause. Of course, the theist still has to find a way to give a positive answer to the bulleted question. I think there are two ways of doing so. First, likely a perfect being would have a preference for greater creaturely participation in creation, and creating the universe in, say, the 10 billion year stage, or indeed in any post-Big Bang stage, would pointlessly cut short creaturely participation in creation (e.g., in the 10 billion year stage, the Solar System would be created ex nihilo, rather than being generated from a star-forming nebula). Second, such a being would be likely to create a world that doesn’t make true what is intuitively to us a “skeptical hypothesis”.

The argument will also please the now-less-common atheist who thinks the universe is eternal.

Complexity and skeptical hypotheses

Suppose a strong epistemic preference for simpler theories of the world. One might then think that a simulation hypothesis is automatically more complex than the best physical story about our world, because in addition to all the complexity of our simulated cosmos, it includes the complexity of whatever physical cosmos houses the hardware running the simulation.

But this need not be the case. The best physical story about our world makes our world include vast amounts of information that would not need to be included in the simulation. To simulate the history of the human race, we at most need information on the particles wihtin a sphere of radius about a hundred thousand light-years, so basically just the Milky Way Galaxy, a very small fraction of the particles in the world. And even that is a vast overstatement. One can surely have a low simulation resolution for a lot of stuff, simulating things only on a macroscopic level, and only including particle-level information when the simulated humans peer into scientific instruments. So the information content of the simulation software could be much, much lower than the information content of the physical world that our best theories say we live in.

But what about the simulation hardware itself? Wouldn’t that need to live in a complex physical universe? Maybe, but that universe need not be as complex as our physical theories claim ours to be. It could be a universe that has a level of physical complexity optimized for running the computing hardware. The granularity of that universe could be much coarser than ours. For instance, instead of that universe being made of tiny subatomic particles like ours, requiring many (but fewer and fewer with progress in miniaturization) particles per logic gate, we could suppose a universe optimized for computing whose fundamental building blocks are logic gates, memory cells, etc.

I am dubious, thus, whether we can rule out simulation hypotheses by an epistemic preference for simpler theories. The same goes for Berkeleian skeptical hypotheses on which there is no physical world, but we are disembodied minds being presented with qualia.

And of course the “local five minute hypothesis”, on which the universe is five minutes old and has a radius of five light-minutes, posits a world with intuitively much less complexity than the world of our best theories, a world with vastly fewer particles.

But if we cannot avoid skeptical hypotheses on grounds of complexity, how can we avoid them?

My current view is that we simply have to suppose that our priors are normatively constrained by human nature (which on my Aristotelian view is a form, a real entity), and human nature requires us to have non-skeptical priors. This is a very anthropocentric account.

Multiverses as a skeptical hypothesis

1. A multiverse hypothesis that counters the fine-tuning argument posits laws of nature that vary across physical reality.

2. A hypothesis that posits laws of nature that vary across physical reality contradicts the uniformity of nature.

3. A hypothesis that contradicts the uniformity of nature is a global skeptical hypothesis.

4. Global skeptical hypotheses should be denied.

5. So, a multiverse hypothesis that counters the fine-tuning argument should be denied.

The thought behind (1) is that the constants in the laws of nature are part and parcel of the laws. This can be denied. But still, the above argument seems to have some plausibility.

Boltzmann brain blackouts

Some cosmological theories lead to the worrisome conclusion that most people with present brain states like ours are Boltzmann brains—random aggregations of molecules in space that came together to form a brain in a little bubble of oxygen. Usually when people talk about Boltzmann brains, they talk of how this induces a sceptical problem for the theory that generates them. Thinking about Boltzmann brain issues that way leads to messy epistemological questions such as whether we get to simply assume that we have hands, and the like. Moreover, if there is evidence for the cosmological theory, then that becomes evidence for Boltzmann brains, which then undermines the evidence for the cosmological theory, and that’s all a mess.

Here is how I suggest we think about what happens when a cosmological theory T leads to a Boltzmann brain issue. The vast majority of Boltzmann brains—even ones with brain states like ours—are short-lived. Their bubble of oxygen dissipates in the absence of gravity, and after a brief moment of hypoxia they die. So think of the point this way. If a cosmological theory predicts a large ratio of Boltzmann brains to ordinary evolved brains, then the theory makes an empirical prediction: in a moment you are extremely likely to start blacking out. So just do the experiment: wait a moment and see if you’re blacking out. If you’re not, then you’ve got very strong disconfirmation of the cosmological theory, and you’re done with it. You don’t have to worry about self-defeat, Moorean questions about whether you have two hands, or anything deep like that. (And if you are blacking out, then if it’s a Boltzmann brain related blockout, you’ll be dead in a moment. If you do come back to, and not in the afterlife, that’s massive evidence against the theory again, but now you should see a doctor about your blackout problem.)

In fact, you don’t even have to wait: on cosmological theories that generate too many Boltzmann brains, you should expect to already be starting to black out—because most of the Boltzmann brains will be extremely short-lived.

Objection: There will be long-lived Boltzmann brains, too.

Response: Sure. But for entropic reasons they will be much less common than the short-lived ones. You might, of course, worry that in many of these cosmological scenarios there are infinitely many Boltzmann brains, and infinitely many are short-lived and infinitely many are long-lived, and you can’t say that the short-lived ones are more common. The short-lived ones will be more common in a “typical” large finite region, but overall we just have infinity. Now, if you are worried about this—and I think you should be—then that worry already applied at the beginning of the story when you looked at the ratio of ordinary to Boltzmann brains, because there will be infinitely many of each on such a cosmological theory, and the formulation of the problem that I gave at the beginning, namely that Boltzmann brains greatly outnumber ordinary brains, is inaccurate. (I think if you do have this worry, then the theory has another problem, namely that probabilistic reasoning makes no sense in a world described by the theory. That is a kind of sceptical and self-defeat problem, but of a different nature.)

My point in this post is modest: if you want to say that Boltzmann brains greatly outnumber ordinary brains, then instead of thinking deep stuff about self-defeat of theories and scepticism, you should just think of the theory that generates this prediction as falsified by future observation.

Trust and scepticism

To avoid scepticism, we need to trust that human epistemic practices and reality match up. This trust is clearly at least a part of a central epistemic virtue.

Now, trusting persons is a virtue, the virtue of faith. But trusting in general, apart from trusting persons, is not. Theism can thus neatly account for how the trusting that is at the heart of human epistemic practices is virtuous: it is an implicit trust in our creator.

Consciousness of one's choices

Here is a plausible thesis:

1. Consciousness of one’s choice is necessary for moral responsibility.

I go back and forth on (1). Here is a closely related thesis that is false:

2. Knowledge of one’s choice is necessary for moral responsibility.

For imagine Alice who on the basis of a mistaken interpretation of neurosience thinks there are no choices. Then it could well be that Alice does not know that she is making any choices. But surely this mistake does not take away her moral responsibility for her choice.

Alice presumably still has consciousness of her choice, much as the sceptic still has perception of the external world. So Alice isn’t a counterexample to (1). But I wonder if (1) is very plausible once one has realized that (2) is false. For once we have realized that (2) is false, we realize that in Alice’s case the consciousness of her choice is not knowledge-conferring. And such consciousness just does not seem significant enough to matter for moral responsibility.

Skepticism and the Principle of Sufficient Reason now online

Rob Koons' and my article "Skepticism and the Principle of Sufficient Reason", forthcoming in Philosophical Studies, is now online.

Humeans should be (Kenneth-)Pearceans

I have long thought that Humeanism leads to strong inductive scepticism about the future—the thesis that typical inductive generalizations about the future aren’t even more likely than not—roughly because there are a lot more induction-unfriendly worlds with our world’s history than induction-friendly ones.

But this argument assumes that there isn’t some extra-systemic explanation of why we have an induction-friendly physical reality. If there is, then the mere counting of worlds does nothing. Now, standard theism provides such an extra-systemic explanation. But standard theism is incompatible with Humeanism, because God-to-world causation is incompatible with the Humean understanding of causation.

However, it’s occurred to me today that there is a non-standard theism that could furnish the Humean with an escape: Kenneth Pearce has advocated a theism on which God explains the contingent world in a non-causal way.

I don’t know of another option for the Humean in the literature. I know of three candidates for extra-systemic explanations of physical reality:

1. there isn’t one

2. there is one, and it’s theistic

3. there is one, and it’s necessitarian (e.g., Optimalism).

The Humean can’t take the necessitarian way out, because Humeanism is strongly opposed to such necessities. The first option leads to inductive scepticism. That leaves 2. But Humeans cannot accept causal theism. So that leaves them non-causal theism.

Animal consciousness

I wonder if a non-theist can be reasonably confident that non-human animals feel pain.

Start with functionalism. The precise functional system involved with feeling pain in us has no isomorph in non-human animals. For instance, in us, damage data from the senses is routed through a decision subsystem that rationally weighs moral considerations along with considerations of self-interest prior to deciding whether one should flee the stimulus, while in non-human animals there are (as far as we know) no moral considerations.

We can now have two hypotheses about what functional system is needed for pain: (a) there needs to be a weighing of damage data along with specifically moral consideration inputs, or (b) there just needs to be a weighing of damage data along with other inputs of whatsoever sort.

We cannot do any experiments to distinguish the two hypotheses. For the two hypotheses predict the same overt behavior. And even self-experimentation will be of no use. I suppose one could—at serious ethical risk—try to disable the brain’s processing of moral data, and prick oneself with a pin and check if it hurts. But while the two hypotheses do make different predictions as to what would happen in such a case, they do not make different predictions as to what one would remember after the experiment was done or how one would behave during the experiment.

Similar problems arise for every other theory of mind I know of. For in all of them, it seems we are not in a position to know precisely which range of neural structures gives rise to pain. For instance, on emergentism we know that pain emerges from our neural structures, but it seems we have no way of knowing how far we can depart from our neural structures and still get pain. On Searle-style biologism, where functionalistically irrelevant biological detail is essential for mental properties, it seems we have no way of figuring out which biological biological details permit mental function. And so on.

I know of only one story about how we can be reasonably confident that non-human animals feel pain: God, who knows everything, creates us with the intuition that certain behaviors mean pain, and in fact these behaviors do occur in non-human animals.

The local five minute hypothesis, the Big Bang and creation

The local five minute hypothesis is that the earth, with everything on it, and the environment five light-minutes out from it, come into existence five minutes ago.

Let’s estimate the probability of getting something like a local five minute hypothesis by placing particles at random in the observable universe. Of course, in a continuous spacetime the probability of getting exactly the arrangement we have is zero or infinitesimal. But we only need to get things right to within a margin of error of a Planck distance for all practical purposes.

The volume of the observable universe is about 10⁸⁰ cubic meters. The Planck volume is about 10⁻¹⁰⁵ cubic meters. So, getting a single particle at random within a Planck volume of where it is has a probability of about 10⁻¹⁸⁵.

But, if we’re doing our back-of-envelope calculation in a non-quantum setting (i.e., with no uncertainty principle), we also need to set the velocity for the particles. Let’s make our margin of error be the equivalent of moving a Planck distance within ten minutes. So our margin of error for velocity in any direction will be about 10⁻³⁵ meters in 600 seconds, or about 10⁻³⁸ meters per second. Speeds range from 0 to the speed of light, or about 10⁸ meters per second, so the probability of getting each of the three components of the velocity right is about 10⁻⁴⁶, and since we have three directions right is something like 10⁻¹³⁸. The probability of getting both the position and velocity of a particle right is then 10^{−(185 + 138)} = 10⁻³²³. Yeah, that’s small. Also, there are about 100 different types of particles, and there are a few other determinables like spin, so let’s multiply that by about 10⁻³ to get 10⁻³²⁶.

The total mass of planetary stuff within around five light minutes of earth—namely, Earth, Mass and Venus—is around 10²⁵ kilograms. There are no more than about 10²⁵ atoms, and hence about 10²⁷ particles, per kilogram. So, we have 10⁵² particles we need to arrange within our volume.

We’re ready to finish the calculation. The probability of arranging these many particles with the right types and within our position and velocity margins of error is:

• (10⁻³²⁶)¹⁰⁵² ≈ 10^{−102.5 × 1052} ≈ 10⁻¹⁰⁵⁵.

Notice, interestingly, that most of the 55 comes from the number of particles we are dealing with. In fact, our calculations show that basically getting 10^N particles in the right configuration has, very roughly, a probability of around 10^{−10N + 3}.

So what? Well, Roger Penrose has estimated the probability of a universe with an initial entropy like ours at 10⁻¹⁰¹²³. So, now we have two hypotheses:

• A universe like ours came into existence with a Big Bang

• The localized five minute hypothesis.

If there is no intelligence behind the universes, and if probabilistic calculations are at all appropriate for things coming into existence ex nihilo, the above probability calculations seem about right, and the localized five minute hypothesis wins by a vast margin: 10⁻¹⁰⁵⁵ to 10⁻¹⁰¹²³ or, roughly, 10¹⁰¹²³ to 1. And if probabilistic calculations are not appropriate, then we cannot compare the hypotheses probabilistically, and lots of scepticism also follows. Hence, if there is no intelligence behind the universe, scepticism about everything more than five minutes ago and more than five light minutes from us follows.

Recognizing the finite

We have a simple procedure for recognizing finite sequences. We start at the beginning and go through the sequence one item at a time (e.g., by scanning with our eyes). If we reach the end, we are confident the sequence was finite. This procedure can be relied on if and only if there are no supertasks—i.e., if and only if it is impossible to have an infinite sequence of tasks started and completed.

How do we know that there are no supertasks? Either empirically or a priori. To know it empirically, we would have to know that the various tasks we’ve completed were finite. But how would we know of any tasks we’ve completed that it’s finite if not by the above procedure?

So we have to know it a priori.

And the only story I know of how we could do that is by a priori cognizing some anti-infinity principle like Causal Finitism.

I am not sure how strong the above argument is. It is a little too close to standard sceptical worries for comfort.

The five minute hypothesis

Let S(t) be the state our universe actually has t units of time after the Big Bang.

Let’s suppose that our universe begins at time 0, i.e., at the Big Bang. Then we can ask this question:

1. Why did the universe begin to exist in state S(0) rather than in one of the infinitely many states S(t) for t > 0?

If naturalism is true, the universe’s beginning as it does is probably a brute (unexplained) contingent fact. And while the state S(0) is rather different in physical arrangement from the states S(t) for t > 0, it does not seem different with respect to the likelihood of brutely coming into existence ex nihilo. So the question (1) is not easily to be dismissed, in the way that one might dismiss the question “Why is the third digit of the gravitational constant in SI units a 7 instead of some other digit?” by saying “Well, it had to something, and there is nothing special about 7.” For there is something special about S(0), namely that it is a singularity state that blocks retrodiction, but this something special does not seem relevant to the likelihood of brutely coming into existence—if only because brute coming into existence cannot be probabilistically quantified.

Theism, on the other hand, provides a satisfying answer to (1). First, as a warmup, we might have a good theistic story why the initial state isn’t S(t) for a very large t: perhaps the universe will no longer be habitable after t, and God has good reason to create a habitable universe. Second, we have a good reason why the initial state should be S(0): a singularity is a natural barrier to retrodiction, and so creating a universe whose past goes back to a singularity is creating a universe where the retrodictive knowledge of beings like us is maximized (cf. Robin Collins’ ideas on our world being optimized for science). And knowledge is good. So God has reason to create a world in initial state S(0).

Technical note: Perhaps there is no singularity state S(0), but instead there are states S(t) for t > 0. If so, then replace S(t) in the above argument by something facts about limits from above of S(t). Abstractly, we can form such units as disjunctions of shrinking conjunctions: let U(t)=⋁_δ>0⋀_0<ϵ<δS(t+ϵ), and say that the universe “begins to exist in state U(t)” provided that it doesn’t exist time t or earlier, but that U(t) correctly describes an opening interval of the universe’s existence. Then replace (1) with the question:

2. Why did the universe begin to exist in state U(0) rather than in one of the infinitely many states S(t) or U(t)?

Mathematical structures, physics and Bayesian epistemology

It seems that every mathematical structure (there are some technicalities as to how to define it) could metaphysically be the correct description of fundamental physical structure. This means that making Bayesianism be the whole story about epistemology—even for idealized agents—is a hopeless endeavor. For there is no hope for an epistemologically useful probability measure over the collection of all mathematical structures unless we rule out the vast majority of structures as having zero probability.

A natural law or divine command epistemology can solve this problem by requiring us to assign zero probability to some non-actual physical structures that are metaphysically possible but that our Creator wants us to be able to rule out a priori. In other words, our Creator can make us so that we only take epistemically seriously a small subset of the possibilia. This might help with the problem of scepticism, too.

Beatific vision and scepticism

One way to think of the beatific vision is as a conscious experience whose quale is God himself. Not a representation of God, but the infinite and simple God himself. Such an experience would have have a striking epistemological feature. Ordinary veridical experiences are subject to sceptical worries because the qualia involved in them can occur in non-veridical experiences, or at least can have close facsimiles occurring in non-veridical experiences. But while everything is similar to God, the similarity is always infinitely remote. Moreover, there is a deep qualitative difference between God in the beatific vision and other qualia. No other quale is a person or even a substance.

Thus, someone who has the beatific vision is in the position of having an experience that is infinitely different from all other experiences, veridical or not. This, I think, rules out at least one kind of sceptical worry, and hence the beatific vision is also a fulfillment of the Cartesian quest for certainty—though that is far from being the most important feature of the beatific vision.

Are we in a computer simulation?

Do we live in a computer simulation?

Here’s a quick and naive thought. We would expect most computer simulations to be of pretty poor quality and limited in scope. If we are in a simulation, the simulation we are in is of extremely high quality and of great scope. That’s not what we would expect on the simulation hypothesis. So, probably, we don’t live in a computer simulation.

But the following argument is pretty convincing: 1. If materialism is true, then probably a computer simulation of a brain can think (since the best materialist theory of mind is functionalism). 2. If a computer simulation of a brain can think, then most thinkers live inside computer simulations.

So, the argument that we don’t live in a computer simulation gives us evidence against materialism.

Realism and anti-reductionism

The ordinary sentence "There are four chairs in my office" is true (in its ordinary context). Furthermore, its being true tells us very little about fundamental ontology. Fundamental physical reality could be made out of a single field, a handful of fields, particles in three-dimensional space, particles in ten-dimensional space, a single vector in a Hilbert space, etc., and yet the sentence could be true.

An interesting consequence: Even if in fact physical reality is made out of particles in three-dimensional space, we should not analyze the sentence to mean that there are four disjoint pluralities of particles each arranged chairwise in my office. For if that were what the sentence meant, it would tell us about which of the fundamental physical ontologies is correct. Rather, the sentence is true because of a certain arrangement of particles (or fields or whatever).

If there is such a broad range of fundamental ontologies that "There are four chairs in my office" is compatible with, it seems that the sentence should also be compatible with various sceptical scenarios, such as that I am a brain in a vat being fed data from a computer simulation. In that case, the chair sentence would be true due to facts about the computer simulation, in much the way that "There are four chairs in this Minecraft house" is true. It would be very difficult to be open to a wide variety of fundamental physics stories about the chair sentence without being open to the sentence being true in virtue of facts about a computer simulation.

But now suppose that the same kind of thing is true for other sentences about physical things like tables, dogs, trees, human bodies, etc.: each of these sentences can be made true by a wide array of physical ontologies. Then it seems that nothing we say about physical things rules out sceptical scenarios: yes, I know I have two hands, but my having two hands could be grounded by facts about a computer simulation. At this point the meaningfulness of the sceptical question whether I know I am not a brain in a vat is breaking down. And with it, realism is breaking down.

In order for the sceptical question to make sense, we need the possibility of saying things that cannot simply be made true by a very wide variety of physical theories, since such things will also be made true by computer simulations. This gives us an interesting anti-reductionist argument. If the statement "I have two hands" is to be understood reductively (and I include non-Aristotelian functionalist views as reductive), then it could still be literally true in the brain-in-a-vat scenario. But if anti-reductionism about hands is true, then the statement wouldn't be true in the brain-in-a-vat scenario. And so I can deny that I am in that scenario simply by saying "I have two hands."

But maybe I am moving too fast here. Maybe "I have two hands" could be literally true in a brain-in-a-vat scenario. Suppose that the anti-reductionism consists of there being Aristotelian forms of hands (presumably accidental forms). But if, for all we know, the form of a hand can inform a bunch of particles, a fact about a vector or the region of a field, then the form of a hand can also inform an aspect of a computer simulation. And so, for all we know, I can literally and non-reductively have hands even if I am a brain in a vat. I am not sure, however, that I need to worry about this. What is important is form, not the precise material substrate. If physical reality is the memory of a giant computer but it isn't a mere simulation but is in fact informed by a multiplicity of substantial and accidental forms corresponding to people, trees, hands, hearts, etc., and these forms are real entities, then the scenario does not seem to me to be a sceptical scenario.

Sceptical scenarios and Quantum Mechanics

It's occurred to me that on most non-Bohmian interpretations of quantum mechanics, we end up being in a superposition of the kind of universe we think we're in and a sceptical scenario, e.g., some brain in a vat scenario, though details of the scenario may differ depending on an interpretation. All that's needed for that to happen is for there to have been a non-zero chance of a sceptical scenario with the same phenomenal states that we actually have. I don't know if this is a problem if the sceptical scenario is assigned low weight by the wavefunction.

A defense of the five minute hypothesis (given a certain false assumption)

Plausibly:

1. If the universe came into existence either for no cause at all or randomly, it is a priori more likely that it came into existence in a higher-entropy state rather than a lower-entropy one.
2. If the universe came into existence fully-formed five minutes ago ("five minute hypothesis"), it came into existence in a higher-entropy state than if it came into existence 13.8 billion years ago ("scientific orthodoxy").
3. So, if the universe came into existence either for no cause at all or randomly, the five minute hypothesis would be a priori more likely than scientific orthodoxy.
4. But there is no a posteriori evidence for scientific orthodoxy over the five minute hypothesis.
5. So, if we think the universe came into existence either for no cause at all or randomly, it is not rationally consistent for us to believe scientific orthodoxy over the five minute hypothesis.

I personally think premise (1) is dubious: I doubt there are meaningful probabilities for the universe to come into existence for no cause at all or randomly. But if there are no meaningful probabilities, then it is not a priori more likely that it come into existence as scientific orthodoxy claims, and the rest of the argument should continue to go through.

Of course, I think we should believe scientific orthodoxy over the five minute hypothesis, so we should reject the no-cause and randomness hypotheses in (1).

An amusing rhetorical way to present the argument is that if the universe came into existence for no cause at all or randomly, we shouldn't prefer scientific orthodoxy to certain young earth views.

I'm probably not a brain in a vat

This is very naive but has only occurred to me:

1. If I were a brain in a vat, I'd expect my experiences to be simple or not very orderly (glitchy); but if I were an ordinary human being as I seem to be, the experiences I would expect would be like that.
2. My experiences are complex, continuous and very orderly.
3. So, probably, I am an ordinary human being rather than a brain in a vat.

Why believe premise (1)? Well, it's hard to hook up all the nine or so senses to simulated data of great complexity. Furthermore, my experiences have diachronic order and complexity over decades. This could be produced by fake memories, but fake memories would likely be hard to impose.

This argument is specific to brains in vats. It might not apply to other sceptical hypotheses.