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Also relevant: Boltzmann Brains https://en.wikipedia.org/wiki/Boltzmann_brain https://en.wikipedia.org/wiki/Boltzmann_brain A Boltzmann Brain is (very roughly

by jzl 10y ago

Also relevant: Boltzmann Brains https://en.wikipedia.org/wiki/Boltzmann_brain https://en.wikipedia.org/wiki/Boltzmann_brain A Boltzmann Brain is (very roughly) a "brain", i.e. self-aware entity, that appears spontaneously in the middle of the universe due to random quantum fluctuations. In an infinitely old and infinitely large universe this should actually be a common occurrence. So why are we not Boltzmann Brains ourselves? Why are we all here observing the universe clustered together on this one planet a mere 15 billion years since it came into being? Why is there so much structure?

zardo 10y ago
>Why is there so much structure? Because complex structures (brains) are much more likely to form out of self-assembling sub-structures than from random noise. And Boltzmann brains wouldn't be on hackernews.
acqq 10y ago
> In an infinitely old and infinitely large universe this should actually be a common occurrence. So why are we not Boltzmann Brains ourselves? Our Universe of 13.8 Billion years (think: just 13.8 G years -- my fingernail-sized camera card has more bytes than that number) is infinitely younger than an infinitely old Universe.
- akvadrako 10y ago
  A year is a lot larger than one byte.
- jzl 10y ago
  I didn't word my post very well (I posted the "infinitely old" comment), but what I meant was that it should be more likely to be a Boltzmann Brain in an infinitely old universe than a human standing on Earth in a ~14 Billion year old universe. So why are we the latter rather than the former? That's basically what the anthropic principle is all about. The fact that we are the latter tells us a lot about how the universe, or universes as the case may be, work.
Analog24 10y ago
I believe the concept is a little different than what you stated. It starts with the assumption that the Universe is actually in or very close to a maximal entropy state, which is orders and orders of magnitudes more likely than the low entropy state we perceive. The idea of a Boltzmann brain is that a downward fluctuation in entropy from this maximum entropy state could result in forming a consciousness with our associated memories and experiences and this is more likely, statistically speaking, than the alternative possibility: that we actually live in an extremely low entropy state of the Universe.
jbmorgado 10y ago
> "In an infinitely old and infinitely large universe this should actually be a common occurrence. So why are we not Boltzmann Brains ourselves?" Because our Universe is neither infinitely old (is about ~14 thousand millions years old) nor infinitely large (is about 90 thousand millions ly in diameter). Now this might seem big for you, but it's actually infinitesimal when compared to the number of necessary permutations in order for higher intelligence to appear solely by a quantum fluctuation. This means that the only scientific possibility for higher intelligence to appear, is then that only a very small set of universe conditions must occur so that atoms then stars then planets then life then intelligent life has the time and conditions to form.
- daxorid 10y ago
  Because our Universe is neither infinitely old (is about ~14 thousand millions years old) nor infinitely large (is about 90 thousand millions ly in diameter) You have just suggested the universe expands at roughly 6c, no?
  - lucozade 10y ago
    That's correct. Current estimates are that spacetime at the edge of the observable universe is expanding at about 6c.
  - jbmorgado 10y ago
    In the early moments after the big bang, the metric of the universe expanded much faster than the speed of light increasing it's size way above the c x t linearity. This doesn't violate relativity though, since what is expanding is the length of the spacial dimensions, but the particles between themselves are moving slower than the speed of light (imagine 2 points in the surface of a balloon when the ballon is inflating).
  - Analog24 10y ago
    The acceleration of the Universe has not been constant. In the very early Universe there was a period called Inflation where the speed of expansion was much much much faster than the speed of light.
pfd1986 10y ago
We can't forget that Boltzmann was purely thinking of (near) equilibrium structures. Structure emerges spontaneously minimizing free-energy, totally OK with LBs high entropy laws.
grkvlt 10y ago
Is there any way to tell that you are not, in fact, a Boltzmann brain with simulated memories and inputs that just imagines everything else exists? I assume it's hard to refute, like Solipsism?

by jzl 10y ago

zardo 10y ago

>Why is there so much structure? Because complex structures (brains) are much more likely to form out of self-assembling sub-structures than from random noise. And Boltzmann brains wouldn't be on hackernews.

acqq 10y ago

> In an infinitely old and infinitely large universe this should actually be a common occurrence. So why are we not Boltzmann Brains ourselves? Our Universe of 13.8 Billion years (think: just 13.8 G years -- my fingernail-sized camera card has more bytes than that number) is infinitely younger than an infinitely old Universe.

akvadrako 10y ago
A year is a lot larger than one byte.
jzl 10y ago
I didn't word my post very well (I posted the "infinitely old" comment), but what I meant was that it should be more likely to be a Boltzmann Brain in an infinitely old universe than a human standing on Earth in a ~14 Billion year old universe. So why are we the latter rather than the former? That's basically what the anthropic principle is all about. The fact that we are the latter tells us a lot about how the universe, or universes as the case may be, work.

Analog24 10y ago

I believe the concept is a little different than what you stated. It starts with the assumption that the Universe is actually in or very close to a maximal entropy state, which is orders and orders of magnitudes more likely than the low entropy state we perceive. The idea of a Boltzmann brain is that a downward fluctuation in entropy from this maximum entropy state could result in forming a consciousness with our associated memories and experiences and this is more likely, statistically speaking, than the alternative possibility: that we actually live in an extremely low entropy state of the Universe.

jbmorgado 10y ago

> "In an infinitely old and infinitely large universe this should actually be a common occurrence. So why are we not Boltzmann Brains ourselves?" Because our Universe is neither infinitely old (is about ~14 thousand millions years old) nor infinitely large (is about 90 thousand millions ly in diameter). Now this might seem big for you, but it's actually infinitesimal when compared to the number of necessary permutations in order for higher intelligence to appear solely by a quantum fluctuation. This means that the only scientific possibility for higher intelligence to appear, is then that only a very small set of universe conditions must occur so that atoms then stars then planets then life then intelligent life has the time and conditions to form.

daxorid 10y ago
Because our Universe is neither infinitely old (is about ~14 thousand millions years old) nor infinitely large (is about 90 thousand millions ly in diameter) You have just suggested the universe expands at roughly 6c, no?
- lucozade 10y ago
  That's correct. Current estimates are that spacetime at the edge of the observable universe is expanding at about 6c.
- jbmorgado 10y ago
  In the early moments after the big bang, the metric of the universe expanded much faster than the speed of light increasing it's size way above the c x t linearity. This doesn't violate relativity though, since what is expanding is the length of the spacial dimensions, but the particles between themselves are moving slower than the speed of light (imagine 2 points in the surface of a balloon when the ballon is inflating).
- Analog24 10y ago
  The acceleration of the Universe has not been constant. In the very early Universe there was a period called Inflation where the speed of expansion was much much much faster than the speed of light.

pfd1986 10y ago

We can't forget that Boltzmann was purely thinking of (near) equilibrium structures. Structure emerges spontaneously minimizing free-energy, totally OK with LBs high entropy laws.

grkvlt 10y ago

Is there any way to tell that you are not, in fact, a Boltzmann brain with simulated memories and inputs that just imagines everything else exists? I assume it's hard to refute, like Solipsism?