The Anthropic Principle (2000)
physics.sfsu.edu
physics.sfsu.edu
On day XX/YY/ZZZZ, Joe hosts a board-game party and a bunch of people show up. During the course of the party, Joe reveals to everyone his d100 policy.
Tim asks him what his die-roll this morning was. Joe tells Tim that he rolled a 1. Tim exclaims "The only reason we're here is because you rolled a 1! How did this incredible piece of luck come to pass?"
Adam responds "There's nothing incredible about what happened. If Joe hadn't rolled a 1 today, we wouldn't be here. We would never have this discussion, or have it on some other day when he does roll a 1."
~This~ morning Joe rolled a dice, and it came up 1, so he hosted a board-game party.
During the party Joe hints that the die he rolls may be very large, but stops short of outright saying so.
Joe also refuses to say whether he rolls the die every morning, or if it was just this morning.
The interesting questions are:
How big is the die?
How often is it rolled?
Does Joe do anything at all if he rolls almost anything other than a 1, or does he just lie in bed?
If the very large die is only rolled once, and all non-1s are very boring, then it is remarkable that we're here.
That's a very interesting point you raised, and I was thinking about this as well. If the universe only "exists once", and life is very unlikely but it still came to be, then it does seem remarkable.
However, this is based on the presumption that life is non-boring, and all other potential universes devoid of life are boring. This seems like a very subjective presumption. Clearly we are biased towards thinking that our own existence, or the similar existence of "life" is special. But a skeptic would claim that from a purely scientific perspective, there's no reason to believe that a universe without life is any more boring than our universe.
To quote neutral milk hotel, "how strange it is to be anything at all"
e.g Q: out of billions of stars what is the chance that this discussion takes place at a planet that can support intelligent life?
A: high
In your case, in 19/20 possible worlds, there will be a group of disappointed friends not playing board games. It is reasonable to look for an explanation of why one finds oneself in the 1/20 case and not in the 19/20 case.
In the anthropic principle, in (N-1) cases there is nobody there to ask the question. Therefore, given that there is an entity capable of asking the question, there is no need to explain why that entity happens to find itself in a universe where question-asking entities are possible. Given that the friends exist at all, there is no need to explain why they are playing cards.
The anthropic principle doesn't answer the question of why there is a universe at all, how many universes there are, have been, or will be, or how many universes have contained intelligence. All it says is that we should not be surprised to find ourselves in a universe where intelligent life is possible, since it would be impossible for us to find ourselves anywhere else.
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?
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.
This is the diameter of the observable universe. We don't know if the universe is infinitely big, but all signs (e.g. the flatness of space as far as we can measure it) point to it being infinite, or very very much larger than our observable sphere.
I don't understand why I'm constantly having to inform smart people of this very basic fact. Is there something wrong with the way we teach astronomy? Can you help me spread the word?
Then picture us as ants on a surface that appears flat as far as we can see. Are we on an infinitely sized surface? Either we are, or it's a sphere but the surface is curved but so slightly that it appears flat. This implies the sphere is much bigger than our observable area.
Note, we're assuming the universe doesn't just end we arbitrary boundaries. It either is infinite or it curves back on itself.
Our observable sphere is nowhere near 90 thousand million ly in diameter since that would violate relativity. Our observable sphere in ly is always smaller than the age of the universe in years (so ~14 thousand million years).
Also, what you said is no fact, basic or not, it's just some misconception you have about cosmology so you should stop spreading that word since you are misinforming people you talk to.
In a nutshell: A Universe that begins in a singularity cannot have an infinite diameter and while it's true that we do calculate the size of the Universe by assuming the expansion rate right after the Big Bang and that rate might be wrong, it still cannot be infinite without violating the major principles of physics and the all big bang theory.
Our observable sphere in ly is always smaller than the age of the universe in years (so ~14 thousand million years)
This ignores the basic fact that the universe is expanding at an accelerating rate. I'm comfortable calling this one a fact. Many 9s behind that confidence percentage (even if the number of nines was recently lowered).
A Universe that begins in a singularity cannot have an infinite diameter
Based on what logic? You are probably imagining an infinitesimally small sphere expanding out and becoming the universe. This is a good description of only our observable universe. There's no reason not to think that point wasn't part of an infinitely large manifold. This would point to an infinitely large universe.
I'm not an expert, but in my curiosity I've spoken to Dr. Don Lincoln from Fermilab about this very topic, so that's the source of my confidence. Along with my own subsequent (armchair) research. I've since followed up and done my best to understand why this misconception is so prevalent. I'm convinced it's because many sources say "universe" when they mean "observable universe", leading to many misconceptions.
You seem as misinformed as most.
And that ignores the basic fact that information about those parts of the Universe didn't have time to arrive yet (that is where relativity is violated). You are mixing the concept of "observable universe" with "observed universe". At a given time, given the expansion rate of the universe you have an "observable universe" (those ~90E9 ly), but it will only be fully observable somewhere in the future, in the present you only get to observe ~14E9 ly). In a nutshell what you are proposing is that we are observing particles with infinite redshift. Or perhaps in a simpler way: You can be observing today parts of the universe that are (for instance) 25E9 ly away today, but you are observing particles of light that left that part of the universe a long time ago so that the c x t condition was never violated.
> "This is a good description of only our observable universe. There's no reason not to think that point wasn't part of an infinitely large manifold. This would point to an infinitely large universe."
Based on the theory of the Big Bang which is the de facto theory accepted by Cosmology. It is true that you could have an infinitely large manifold and that is a very interesting theory. But I was answering inside the actual theory that is the accepted one now-a-days the Big Bang (and I actually referred that in the answer). Also, even inside the manifold theory theory, our universe that is what is being discussed here, would still not have an infinite diameter.
Furthermore, your reference to relativity is also incorrect. The expansion of the Universe is not caused by objects moving away from each other, which would be limited by the speed of light. The expansion of the Universe is actually an expansion of space itself, which is not limited by the speed of light. You should look up the "metric expansion of the universe".
In general, relativity is known to be incomplete on a cosmological scale. The situation is much more complicated due to the existence of dark energy and dark matter. You should read about the Lambda-CDM model if you want to learn more about the state of modern cosmology.
I never said that and in fact I explained that the issue here is the metric of the universe expanding, not the particles moving away from each other.
> "is a difference between the size of the observable Universe now and the size when the light was emitted"
Nope, I also never said that.
Seriously just go read what I actually wrote instead of writing whatever goes in your mind with no regard for what is actually being discussed.
You could just clarify your statements/reasoning to try and progress the discussion instead of getting overly defensive.
I was the one explaining to the OP of the thread that the universe is 90E9 ly in diameter (and also, just to clarify for the future so that it doesn't get mixed up yet again, that this is just an approach based on what we know about the history of the universe), it is therefore ridiculous that I also said that it violates relativity. So, sorry if I'm "overly defensive" about you mixing everything up and me having to use my time to answer you so that you don't twist everything I said on the thread.
His other fact is also pointless - it doesn't matter how old the universe is now; the idea is that most Boltzman brains will form in the future.
2nd. The great grandparent asked: "So why are we not Boltzmann Brains ourselves?" and that's what was being answered.
I hope that this teaching will get you to accept it...
The current accepted size of the observable universe is ~90 billion light years in diameter. If you were referring to some other statement that you think violates relativity then feel free to clear things up.
if you're upset about people making assumptions about your comments then (calmly) address those and clarify your point(s). Don't make aggressive and pejorative assumptions of your own.
The statement was made about the infinite size of the Universe and the OP (along the way) was talking about the observable Universe. He is mixing the extent of the Universe with the spatial dimensions of the Universe (so, the better word here is actually space). It is still an open debate if the dimensions of the Universe (space) are infinite (although what we knows seems to point that way), but the extent of the Universe is not infinite, if it was, that would violate relativity (or the standard model as I explained along the thread).
You have just suggested the universe expands at roughly 6c, no?
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).
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.
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.
Can this be seen as evidence that the timeline of humanity will be relatively short in the big picture? Because it would seem like a strange coincidence to be born at the beginning of it. This is even more true for the survival time of humans with modern technology. Assuming the era of technologically advanced humans will last for, say 200M years, it's extremely unlikely to be born at the first 100 years (0.00005 %).
It's interesting to think about how civilization would develop over hundreds, thousands or thousands of thousands years. There have been some pretty significant changes in just the last 100 years, what could happen in millions of years? Civilisation is not a stable system, it seems to be quite volatile. And unlike before, changes and disruptions are not as locally constrained. Perhaps after many thousands of years, there will come a low-probability event that civilization won't recover from.
Imagine you are a soul, in limbo, somewhere outside the universe and elsewhere in another part of reality the universe is progressing through its motions as time goes on. You are an other-reality-style being, yet somehow still allocated as "going to be a homosapiens on Milky Way\Sol\Earth", and your birth will be random during the era of homo sapiens.
Now you can argue about the likliehood of where this random birth happens.
On the other hand, take away the other place, and the souls, and the spooky assignment of types, and just look at the universe as a thing of matter and energy. Some configuration of matter was born to your parents, from their DNA. It is intimately connected to its surroundings by a continual stream of light, heat, air pressure, physical pressure; over millions of seconds it learns. It learns the patterns of air pressure that correspond to other people talking to it, and it learns what things it can and can't push by trying, and what other people talk about.
And it says "isn't it unlikely that I was born here and now, instead of some other time?"
And the question makes no sense. _What_ could have been born somewhere else? or somewhen else? Without its parents DNA, without its particular twenty continuous years of sensory input that it learned from, it would not be itself.
Some other matter, born to other parents, with other DNA, and other childhood experiences, and other knowledge patterns. It would be someone else. Entirely someone else. And ... that happens, we call it "other people".
If you don't believe in a soul, or something like it, what does it mean for you to possibly "be born somewhen else"?
Which is what I was answering. You can't pick a human at random including from the future, unless you're outside the system somehow.
Humans are good at dealing in counterfactuals. 'What would have happened if I hadn't missed the bus?' is a useful question to ask, even if you did miss the bus. What would I be like if I hadn't gone to university/had taken that job/never killed my parents? Obviously the 'I' in those questions cannot be you, exactly, since you did or didn't do those things. But it's still a useful concept or thought experiment, and can give us valuable insights.
The commenter is using 'I' in that counterfactual sense. And certainly, I understood what they meant by it, so they were successful in communicating (at least, to me) which is what matters with language.
similar example - throw a coin 21 time and record result. Now look at that recorded result and behold how unlikely that result is, like one in 2^21 (0.00005%), yet you got it despite the odds :)
In a Bayesian point of view, let's pick some prior probability distribution over lengths of human survival and consider the current age of humanity as a random variable. This gives the posterior probability over lengths of human survival.
I do think that analyzing the stability and trajectory of civilization is very interesting.
> The UU Professor of Anthropics had developed the Special and Inevitable Anthropic Principle, which was that the entire reason for the existence of the universe was the eventual evolution of the UU Professor of Anthropics.
> But this was only a fomal statement of the theory which absolutely everyone, with only some minor details of a `Fill in name here’ nature, secretly believes to be true.
"Then there was the question of why the sun came out during the day instead of at night when it would be more useful."
This is a misunderstanding of what quantum waveform collapse is. It requires an "observation", but not an intelligent observer. For example, in the Schrodinger's Cat thought experiment, the Geiger Counter is a perfectly valid observer.
1. https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
So once a photon is detected, like by making a mark on a screen or camera, it's permanent. In the delayed-choice experiment this happens twice, once for the "interference pattern" and again after the choice.
If you accept that, which I think is intuitive, then it makes the DCQE much easier to grasp. If you want to understand the experiment better, I would recommend this thread:
https://www.physicsforums.com/threads/who-is-puzzled-by-the-...
Duh. Not so insightful as it sounds with a big "principle" name. And other "big named" variants are even less reasonable to be considered.
"NOT Universe can support intelligent life -> NOT Universe can be oberved"
... rather than ...
"Universe can be observed -> Universe can support intelligent life (-> Universe has values which can support life)"
I'm not sure either is more useful than the other.
(I suspect that this page states the weak version in that way in order to make the other versions seem more similar.)
I don't but that an "intelligent" observer is needed to collapse the waveform, BTW. That uses a very non-physical interpretation of "observer." Any particle that can absorb information, can be said to be "observing." As simple as a reaction that depends on temperature would do it.
How can you propose someting like that? I mean, in a scientific way.
"Once intelligence has evolved and observed the Universe with a single first thought, why didn't it then die out?"
What proof, line of reasoning, logical principle, or evidence do you have to believe that a single first thought would lead to anything dying out? What makes you think there is some underlying Anthropic Principle at work in the universe?
Saying something could be at work is more or less saying "God did it". It doesn't explain or illuminate anything.
Once that single first thought by an intelligence has occurred, the Weak or Strong Anthropic Principle is no longer required to explain the existence of intelligence, and so its continuance has the same unlikeliness as other life forms, i.e. ultimate extinction. The fact humans became the opposite of extinct (e.g. fire, scrolls, nukes) suggests that if the Anthropic Principle applies to the emergence of intelligence, something even "stronger" such as the Final Anthropic Principle could apply to the continuance of intelligence.
I'm not saying there's an underlying Anthropic Principle in the Universe. I'm answering the question to show that the Final Anthropic Principle is as scientific a proposal as anything else.
Here's a review: http://www.fourmilab.ch/documents/tipler.html
And here's a quote from it: "it would be possible for each male to be matched not merely with the most beautiful woman in the world . . . but to be matched with the most beautiful woman whose existence is logically possible."
verifiable here: http://articles.chicagotribune.com/1994-11-30/features/94113...
I have his previous book, co-written with John Barrow, The Anthropic Cosmological Principle. It's taken more seriously.
(a) if they were any other shape (e.g. very long isosceles triangles) conditions wouldn't be suitable for intelligent life to evolve, and we wouldn't be around to observe it, or
(b) Newton's law of gravity constrains them to conic sections. Stable orbit of single planets must be circular or elliptical. Any planets with highly eccentric orbits would have been ejected from the early solar system, leaving only those which are roughly circular?
Of course, the answer is (b), i.e. instead of the emergence of intelligent life determining the laws of physics, the laws of physics allow the evolution of intelligent life. But we only agree on that because we already know Newton's law of gravity. If we didn't know it, some people would believe (a) while others would think that one day a law of gravity would be found which determines planetary motion.
The anthropic principle is not about intelligent life determining the laws of physics. There is no magic there. You have the causality backwards.
I don't have the causality backwards. We don't have a complete knowledge of the laws of physics, and we have something which is unexplained. Whenever this was the case in the past, better laws were found which closed the explanatory gap. Why should it be any different this time?
We could find that the laws of our universe are the only possible set of physical laws. This would be the expectation of the Newtonian era. In that case there is nothing to explain. Or it may be, and currently seems likely, that there are many possible sets of physical laws. Then the question of why we happen to have one of the perhaps very few possible sets of physical laws that allows intelligent life to develop seems to require an explanation. The anthropic principle explains why it really doesn't, because in the (possible or actual) universes where intelligent life is impossible, the question simply doesn't come up.
The point of the anthropic principle is precisely that we shouldn't expect to close the explanatory gap, because there isn't one. We shouldn't be surprised if physical laws seem to be "tuned" to allow intelligent life to emerge.
Imagine that planets orbited in randomly selected geometric shapes, and we happened to be on the only known elliptical one, giving us the conditions required for life. Would this lucky fact require explanation?
No more than the existence of a planet of the right size at the right distance from the sun. You still have physical laws which determine what's possible, but they probably won't (and, in fact, don't) provide a complete explanation.
The weakest form of the Anthropic Principle is uncontroversial. For example, we can use it to conclude that physical laws which don't permit intelligent life to evolve must be wrong. Can we use it to rule out physical laws which don't entail the evolution of intelligent life? I would argue yes, but that doesn't require any fine-tuning of dimensionless constants: an infinite (e.g. Einstein-de Sitter) universe, or Everett's Many Worlds interpretation of quantum mechanics would entail it, given its possibility.
Not a bad guess!
If we were so intelligent, we wouldn't have to ask, so the answer is 42.