Boltzmann brains

[unixronin]

New Scientist for August 18-24 contains an article talking about Boltzmann brains and the nature of the Universe.  (The concept of the Boltzmann brain is basically this:  We know elementary particles are constantly popping in and out of existence from quantum vacuum fluctuations.  Occasionally, entire atoms pop into existence in this way.  The more complex a construct, the lower the probability of its spontaneous appearance.  Theoretically, given a sufficiently large space and a sufficiently long time, quantum fluctuations should cause complete functioning consciousnesses able to observe the Universe to spontaneously pop into being.)  Much of the thread of the article seems to center around discussion of how crucial it is that Boltzmann brains never outnumber physical human observers, because if that happened we wouldn't be typical of the Universe, and everything we know might go poof.

Oh, boy.  There's that old anthropic bugbear raising its head again.  Let us suppose that tomorrow, some theorist irrefutably proves that, 10^{10^30} years from now, Boltzmann brains will dominate the Universe.  Would his proof cause the universe as we know it to suddenly disappear in a flash of logic?  I rather doubt it.  (In fact, were we able to somehow prove that Boltzmann brains becoming the majority obeservers of the Universe would cause the end of existence as we know it, it would logically follow that, at least for now, such quantum observers do not outnumber us.)  Does it even MATTER whether we are typical observers of the Universe, or whether our little corner of it is typical?  Again, I rather doubt it.  Nothing that happens to the Universe in the deep future can possibly affect the demonstrable fact that right now, we and our little hospitable corner of the Universe exist.

I propose that we will never fully understand the Universe, so long as our theories about the nature of the Universe are unconsciously built atop a foundation that says it is necessary we remain somehow significant to the Universe, even if only by virtue of being a typically representative sample of it.  I roll to disbelieve that the Universe as a whole gives a blind tinker's damn (figuratively speaking, of course) whether we exist or not.

This, I think, is modern science's version of arguing about how many angels can dance on the head of a pin.

Comments

[meglimir.livejournal.com]

Why would being typical (or not) affect whether we perceive something to exist?

[unixronin.livejournal.com]

Good question. The fractured chain of reasoning appears to go something like this:

1. We're the most important observers of the Universe, therefore it's really important that we be typical, otherwise the Universe as a whole might not be as we perceive our region of it. (No proof or justification given of the importance maxim.)


2. Boltzmann brains are not like us, therefore they might perceive the universe differently than we do.


3. (Unexplained logic implying that somehow, what the observer perceives creates reality, rather than reality defining the scope of what's there for the observer to observe)


4. Boltzmann brains might someday outnumber "ordinary" observers.


5. Oh noes!!!1! What if their perception of reality outweighs ours? We might not be around, 10^{10^30} years from now! (Like we expect to be ANYWAY ... that's far, far beyond the age of baryonic matter. I think the estimates are that all the protons in the Universe will have decayed something like 10¹⁶⁰ years from now.)

Personally, I think it comes down to people with too much time on their hands and not enough real work to do.

[johnkzin.livejournal.com]

2. Boltzmann brains are not like us, therefore they might perceive the universe differently than we do.


There's a MIGHTY big assumption there.

Yes, IF THEY EXIST AT ALL, they come into existence in a manner which is fundamentally different from what we BELIEVE to be the origin of our existence and consciousness. And MAYBE that means that they perceive the universe in a different way than we do. And MAYBE that means that their observation of their corner of the universe will have different fundamental laws than ours. So, IF * MAYBE ^ 2 doesn't strike me as a huge possibility.

I'm not terribly worried. I'm willing to bet its less probable than being killed by pirates, or a toppling vending machine. And, we all know what that means.

(incidentally, #3 isn't a very uncommon interpretation of quantum mechanics; I forget what it's called, but it basically takes "the observer affects the observation" statement to the extreme of saying that the observer, even unconsciously, dictates the observation ... of course, that assumes a lone observer, and how much affect it has is on the quantum scale, so it's not like they're exactly saying you can successfully will a gold bar to appear on your desk ... but my point is: I have a lot more respect for #3 than I do for #2 ... and a lot more respect for #2 than for #5)

[unixronin.livejournal.com]

Personally, I think even assumption #1 is highly suspect in itself. I think the whole idea that we have to be somehow significant in the universe is a kind of cosmic tunnel vision. We may have abandoned first the geocentric universe, then the heliocentric one, but it seems we still simply cannot conceive of the idea of a cosmos to which our existence is utterly irrelevant. We seem to have a psychological need to believe that somehow, it matters to the universe that we're here. Isn't it enough that we are here?

As you point out, there are many maybe's involved in the entire chain of reasoning, and considering that the probable timeframe for the appearance of significant numbers of Boltzmann brains exceeds the believed lifetime of the universe so far by more orders of magnitude than there are believed to be elementary particles in the universe, I find it pretty hard to get excited about the possibility. And let's face it - by that time, the universe WILL BE radically different anyway according to current theories, because all baryonic matter will have long, long, LONG since decayed.

There's a word for this type of speculation, but I can't quite bring it to mind. Not sophistry, not solipsism ... but something akin to those.

[unixronin.livejournal.com]

Oh, and I meant to add, yes, at the quantum level our best models seem to indicate that one cannot observe an event without influencing it in the process. But as far as we can tell, that effect is significant only at close to the quantum level, and has long since disappeared by the time we reach the scale of everyday objects, let alone the universe as a whole. If I look at a plant in my front yard, the photons by which I see it have already completed any interaction with the plant that they're going to before they even reach my eye, and that interaction is unchanged by whether or not my eye happens to subsequently capture those photons (i.e, by whether or not I happen to look out the window).
Apart from anything else, we observe most of the universe as it was long before we even existed to observe it. If our observation of an object so far away that the solar system didn't exist yet when the light we're observing it by began its journey to us, changes that object in time for us to observe the change, then causality is broken and practically the entire structure of physics as we know it collapses.

[johnkzin.livejournal.com]

If I look at a plant in my front yard, the photons by which I see it have already completed any interaction with the plant that they're going to before they even reach my eye, and that interaction is unchanged by whether or not my eye happens to subsequently capture those photons (i.e, by whether or not I happen to look out the window).

That's not necessarily true. There was a paper several years ago that I read where they looked at light coming through the gravitation lens of galaxy A from galaxy B. They were able to perform the standard wave interference vs particle experiments on the light ... observer affecting outcomes of events that happened millions or billions of years ago.

I also heard about (but didn't see a paper for) an experiment where pictures were taken of events and then data randomly sampled to look for particles vs waves, well after the events happened and the pictures all turned out to match the observations (as in, you couldn't look for a particle in the data, and then hope to see a picture of wave interference in the picture, getting around the problem that way: if you looked for a particle in the data, you got a picture of particles, if you looked for wave patterns in the data, you got a picture of waves ... even though both the revelation of the picture and the analysis of the data were both happening well after the event in question).

So, it's not unreasonable that you're affecting the photons hitting the plant, even though the photons aren't getting to your eyes until much later.

Time doesn't play the role that we think it does, in these situations :-}

[unixronin.livejournal.com]

That's not necessarily true. There was a paper several years ago that I read where they looked at light coming through the gravitation lens of galaxy A from galaxy B. They were able to perform the standard wave interference vs particle experiments on the light ... observer affecting outcomes of events that happened millions or billions of years ago.

Well, that's one interpretation. I don't buy the idea that there's retroactive causality taking place — I think it's just that you can observe wave/particle duality in light regardless of how long it took the light to reach you or from how far away, simply because photons exhibit wave/particle duality.

As for roles played by time, I don't think we really understand time well enough to be able to say what it does. We still can't be sure it's not merely a perceptual illusion.

[smandal.livejournal.com]

Well, we can only see about 10 megaparsecs anyway :)

[unixronin.livejournal.com]

Indeed. :) And if, as the article implies, any given Boltzmann brain is likely to only exist for a microsecond before vanishing back into the quantum vacuum, it's only going to have an observational horizon of about three hundred meters anyway.

[lisa-marli.livejournal.com]

OK, Now My Brain hurts.

[plutosonium.livejournal.com]

Theories predicated on the importance of humanity in the cosmos have always annoyed me. How self-important! All they can do is obscure the truth.

[unixronin.livejournal.com]

I agree. When we observe the universe and expound theories based on our observations, we need to do so keeping in mind that there exists precisely zero evidence that the universe is here for our specific benefit.