I What multiverse model is this author referring to?

John's Barrow book "The Constants of Nature" in chapter 13, he talks about a hypothetical multiverse composed of universes governed by other logics. Specifically, he talks about different approaches that physicists take when studying the multiverse, and he mentions a radical approach where even logic could change from one universe to another. But he does not specify any multiverse model...So what is he talking about? Is it there any multiverse model where even the fundamental logic of universes could change?
 

haushofer

Science Advisor
Insights Author
2,169
529
Not within the three frameworks of physics (MWI, inflation and the string landscape) as far as I know. It seems like wild speculation.
 

ohwilleke

Gold Member
1,422
347
It is popular in cosmology to imagine that there are many possible laws of nature all of which exist in one universe or another to try to explain why our universe is the way that it is, often in conjunction with the anthropic principle.

The problem with this approach is that this is done using Bayesian statistics with an arbitrary "prior" expectation concerning how the possibilities are distributed that has no empirical basis, which makes it purely speculative.

Many critics of this approach are loathe to even call this kind of approach "scientific" but it is used by a fair number of professional trained and employed theoretical physicists.
 
It is not clear what a universe obeying a "different logic" means. If we observe such a universe from the outside, it will certainly obey our laws of logic. If we watch a movie about a mental institution, the logic of the inpatients may be broken, but our own logic does work.

Ludwig Wittgenstein pondered if 2 + 2 = 4 is an empirical fact or somehow dictated by logic. We may imagine a universe where every internal observer at every experiment would observe 2 + 2 = 5. Then one might say that the universe obeys a "different logic", for the observers living inside that universe.

If everything in a universe would happen in a random way, then "logic" would not be of much use for the creatures living there.
 

MathematicalPhysicist

Gold Member
4,083
132
It is not clear what a universe obeying a "different logic" means. If we observe such a universe from the outside, it will certainly obey our laws of logic. If we watch a movie about a mental institution, the logic of the inpatients may be broken, but our own logic does work.

Ludwig Wittgenstein pondered if 2 + 2 = 4 is an empirical fact or somehow dictated by logic. We may imagine a universe where every internal observer at every experiment would observe 2 + 2 = 5. Then one might say that the universe obeys a "different logic", for the observers living inside that universe.

If everything in a universe would happen in a random way, then "logic" would not be of much use for the creatures living there.
2+2=4 is true by definition of 4.
So it would work in every universe possible.
 

Klystron

Gold Member
335
352
And at least one branch of Wittgenstein's philosophy Logical positivism fell out of favor well within the 20th Century particularly after work by Karl Popper, among others. (https://en.wikipedia.org/wiki/Karl_Popper#Philosophy_of_science).

Popper's approach to the statement 2+2=4 appears simple but may offer guidance to understanding the implications of the original post.
Popper's solution[45] was an original contribution in the philosophy of mathematics. His idea was that a number statement such as "2 apples + 2 apples = 4 apples" can be taken in two senses. In one sense it is irrefutable and logically true, in the second sense it is factually true and falsifiable. Concisely, the pure mathematics "2 + 2 = 4" is always true, but, when the formula is applied to real-world apples, it is open to falsification.
 
Klystron, exactly. If I put 2 + 2 apples in a bag and always can count 5 apples when I empty a bag, then I conclude that 2 + 2 = 5 in the physical world. We can imagine a universe where every observer at every situation will count 2 + 2 = 5.

An outside observer may see that the observers living in that universe always make a counting error. Or he may see that apples materialize from nothing. For the outside observer, 2 + 2 = 4, but internal observers will find the rule 2 + 2 = 5 more useful.

One may claim that the rules of logic are an empirical fact for the internal observers. They are not dictated by some Platonic mathematical universe.
 

MathematicalPhysicist

Gold Member
4,083
132
And at least one branch of Wittgenstein's philosophy Logical positivism fell out of favor well within the 20th Century particularly after work by Karl Popper, among others. (https://en.wikipedia.org/wiki/Karl_Popper#Philosophy_of_science).

Popper's approach to the statement 2+2=4 appears simple but may offer guidance to understanding the implications of the original post.
2+2=4 doesn't concern itself with apples, it's a tautology.
2 apples +2 apples will not equal 4 apples just in case one apple does some transformation that adds another one to it. (like in the Banach-Tarski paradox, which is not physical as far as I can tell no physicist has been using this type of maths in his reasoning).
 

Want to reply to this thread?

"What multiverse model is this author referring to?" You must log in or register to reply here.

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top