As our video games become more and more lifelike, it's becoming clear that at some point, perhaps soon, our simulations will be indistinguishable from reality.

If that's true, how do we know it didn't already happen?

Could we be in a simulation now?

10 00:00:29,600 --> 00:00:31,190 Before I get into details, I want to share with you a conversation I recently had about this idea with my colleague at the Hayden Planetarium in New York City.

In fact, with its director Neil deGrasse Tyson, along with comedian Eugene Mirman, as part of Neil's "StarTalk" radio show.

I'm Leo Zua-- Zusa-- on Instagram.

How about the recent articles about the possibility of us being part of a simulation and the Big Bang being just the seeding event of such a simulation.

Thanks!

I'm totally there.

Yeah.

I'm digging it.

Every minute of it.

You don't like it?

Yeah?

I'm loving it.

I want to hear your-- I'm loving it.

I want to hear this.

I'm loving it.

Well, so who made the simulation?

Some snot-nosed kid in the parents' basement of an alien civilization, who's bored, and they're more advanced than we are, and they have way more computing power than we are-- Right, so it's like a little handheld Nintendo you can do-- Exactly.

And so they program in enough detail to completely simulate every molecule in this universe.

And we are here for their entertainment.

Why else can you explain, where things are going along just fine in the world, that all of a sudden, there's a complete disruption.

The snot-nosed kid?

Culturally, politically, economically, a complete disruption-- I think they throw it in for entertainment.

That's what I think.

OK, I'm going to say.

I have two things to say.

Firstly, I predict that you don't believe that.

That's my first prediction.

OK.

I'm not going to, I don't know, put thought in your head.

That's an argument for why that that's more likely than any other scenario.

I'll tell you that in a minute.

But the numbers game, OK?

So the idea that if you need to produce one universe capable of producing universe simulations.

And that's all you need.

And if that universe produces billions of universe simulations, then any universe that you happen to find yourself in-- is more likely to be one of them-- Than the one universe that started it all.

The way that virtual reality now exists, and you know, video games have advanced, it is likely that, in say, 1,000 years, whatever our virtual reality would be-- Or 30 years.

30 years.

[LAUGHTER] A thousand or 30.

Well, 30 years, whatever it was, would potentially be physical.

Like you would be able to feel it.

OK, so, no, no, no, it doesn't even require that.

It just requires that what you program in there has-- in your Nintendo, whatever it is-- has enough complexity that in the mind of the characters in that game, they think they're real.

Right.

So-- It had free will.

It can't simulate the whole universe, because to simulate a universe perfectly, you need a computer the size of a universe.

Do you?

Do you?

Yes.

I don't know.

Because-- I mean, assuming it's a perfect-- Dub, dub, dub, dub!

The conversation goes in lots of fun directions.

You can check out more on "StarTalk" radio, link in the description.

Now Neil uses an entertaining example of us being a Sims game for hyper advanced alien basement dwellers.

That's a hilarious image.

But he's illustrating a very serious point.

That under certain assumptions, virtual minds should vastly outnumber real minds in our universe.

If so, shouldn't we be virtual minds?

Let's dive deeper into this rabbit hole and decide if this actually makes sense.

But before we do so, we should be clear about what type of simulation we're talking about here.

Let's avoid the idea that the entire universe is simulated, right down to every atom, electron, or vibrating quantum field.

That is a much deeper rabbit hole, one we'll need the holographic principle to explore.

It's a whole big thing, and we'll get back to it.

Instead, today I want to talk about the idea that it's our experience of the universe that is simulated.

That we are simulated minds in a virtual universe that has just enough detail to convince us of its reality.

I'm talking about so-called ancestor simulations, an idea proposed by Oxford University's Nick Bostrom.

It goes like this.

Bostrom argues that in the future it will be possible to simulate the action of all the neurons of the human brain and to simulate the sensory input to that brain with enough fidelity to convince the simulation that it's a real person.

Now that's not too much of a stretch.

There's a good chance we'll be able to do that within a generation or two.

However, Bostrom crunches the numbers to show that a super advanced civilization could do this on such a scale that these sorts of virtual minds vastly outnumber real minds.

Why would they bother?

For science-- he proposes that an advanced civilization may want to run simulations of its own history to study the behavior of the types of minds that lived that history.

He calls these ancestor simulations.

Let's look at the numbers.

The human brain has 100 billion neurons and well over 100 trillion synapses.

It's been estimated that the entire operation of a single brain could be simulated with somewhere between 100 trillion to 100 quadrillion binary operations for every second of time that the brain experiences.

Bostrom argues that it doesn't take anywhere near that much computing power to then simulate an external environment with the fidelity needed to fool the virtual brain that its environment is real.

That's debatable, because the environment needs to be perfectly consistent with respect to all measurements made by all brains in that environment.

But whatever, let's go with Bostrom's assumption.

A full ancestor simulation would simulate all humans that ever lived, going back, say, 50,000 years.

It's estimated that around 100 billion people have lived and died.

An average 30 year lifespan gives each of them a billion seconds.

And each of those seconds requires 10 to the power of 14 to 10 to the power of 17 operations.

Multiply those numbers together, and you get 10 to the 34 to 10 to the 37 binary operations to simulate all of human history.

Bostrom say 10 to the 33 to 36, but potato, potahto.

You can mess with any of those numbers and still remain within those few factors of 10.

So how long would that take to compute for a super advanced civilization?

Well, Bostrom uses Robert Bradbury's estimate-- that a computer the size of a large planet, a so-called Jupiter brain, would be capable of performing 10 to the power of 42 operations per second.

In other words, it will be capable of simulating the entire mental lives of all humans in history a million times over every single second.

Just one such computer would generate an insanely large number of lifelong mental experiences that are indistinguishable from the type of mental experience that you and I are having right now.

That's true, even if you scale back, say, to a computer the size of the moon, or if you assume several more orders of magnitude in the computing power needed to run the simulation.

Bostrom claims the following, which he calls the simulation argument.

If ancestor simulations are something that even some civilizations end up creating-- so if they advance far enough, and decide it's a good idea-- then most of the self-aware minds that ever come into existence will be simulated ones.

Therefore, we are an ancestor simulation.

This sort of existential angst about disembodied brains being more common than real ones didn't start with Bostrom.

The thought experiment is similar to that of the Boltzmann brain.

The idea is that in an infinite multiverse, it should be vastly more common for particles to randomly assemble into a brain that is having exactly your current experience of the world than for particles to randomly produce big bangs.

We talk about that in our last episode.

But both ancestor simulations and Boltzmann brains require us to invoke something like the Copernican principle.

It tells us that we aren't in a special place in the universe.

We're on a typical planet around a typical star in a typical galaxy, with one exception.

Our place in the universe must have been able to produce and sustain us, so we're somewhere habitable.

That last addendum is an application of the anthropic principle.

We must observe a universe or a part thereof that can have observers.

Copernican reasoning with a dash of the anthropic principle tells us that we should be the most typical, the most common type of observer, that could possibly be having our current experience.

So if the virtual minds of an ancestor simulation are vastly more common than the minds of the original living creatures that made the simulation, and if the simulated experience is completely consistent with our own experience, then it's more likely that we are those more typical observers.

I should note that Bostrom is on record as placing the odds at less than 50% that we're a simulation.

Why?

Because he thinks it just as likely that either all civilizations die out before being able to make vast scale ancestor simulations, or essentially no super advanced civilizations choose to make them.

The ancestor simulation idea suffers from some of the same issues as the Boltzmann brain idea.

We already talked about Sean Carroll's argument against concluding that we are Boltzmann brains.

As soon as we do so, we must also conclude that we probably don't have the capacity to have carried out that line of reasoning in the first place.

A Boltzmann brain is as delusional about the consistency of its mental faculties as it is about its existence before that instant.

Similarly, in the case of ancestor simulations, upon deciding that we are simulated, we acknowledge that there is no experiment that we can do to prove that we are not.

The hypothesis is unfalsifiable.

Bostrom himself points out that, upon being found out by one of its resident minds, the simulation can be instantly edited or rewound.

In fact, this editability is a necessity.

These simulations can only cover a tiny fraction of the universe.

So they are prone to inconsistencies.

It's far more computationally economical to edit out the discovery of these inconsistencies than it is to simulate enough of the universe so that inconsistencies don't happen.

Another big issue is just the potential for spectacular overreach in using these Copernican and entropic arguments.

Bostrum himself even weighs in on this with regards Boltzmann brains.

He posits a type of Bayesian reasoning, so assessing the probability of the hypothesis being true by taking into account prior probabilities.

Imagine a philosopher telling a cosmologist that we must surely live in a universe capable of producing the most brains, because that universe would give the maximum probability of our own existence, which is the one thing we know for sure is true.

Therefore, scientists should come up with cosmologies that generate the most minds.

The universe that has the most minds must be the one we're in.

Bostrom labels this the presumptuous philosopher problem and warns against such reasoning.

But I wonder if he needs to reject his own ancestor simulation idea on the same grounds.

Highly specific scenarios like ancestor simulations or Boltzmann brains generate impossibly large numbers of minds that are identical to our own.

But where do you stop?

With a little imagination, yet more mind factory universes can be conceived and simulated "usses" multiply exponentially.

Which type of fake you are you?

Just for now, I strongly recommend that we proceed as though we are real life observers, part