As the others here are implying, the current consensus in the Physics community is that the many worlds hypothesis is not falsifiable, and so should be disregarded in favor of funding theories that can be proven or disproven. String theorists, the biggest proponents of the many worlds theory, are generally ostracized from greater physics academia since they have failed to produce any experimental designs to validate their claims for several decades after taking up a lot of tenured positions in the 90's, along with the "pop science" PR campaigning for their position that started then with some popular books and continues to this day in the works of Michio Kaku for example.
Scientifically, we cannot yet talk about theories that are untestable and unfalsifiable. Sure, math or some other theory may imply other dimensions or parellel universes, but how will you measure one?
Would a ruler suffice?
Oof sorry. Gonna need a protractor.
That doesn't measure up for me.
Is that a tractor that lost its amateur status?
Yeah, he took a case of blueberry jam from the neighbor after he helped them out one day, plowing their fields while their Deere was broken down amd they waited for an expert to fly in from Portland.
Cost his team the championship. Forfieted the entire season.
Scientifically, there are no theories that are untestable and unfalsifiable.
How can you test/falsify the existence of something you can't interact with in any way?
Most likely you couldn't. But sometimes you can be aware of something (X) simply by seeing the effect it has on other things, even if you can't directly observe X. Think of Pluto, dark matter and dark energy; didn't/don't know what it is, but we know something is there.
My original comment was pointing out that a scientific theory is a framework that takes into account all the data. So something that is untestable and unfalsifiable definitionally could not be a theory. You'd be in hypothesis territory at best, but likely just conjecture.
Right, thanks for the clarification. Although in this context, the "theory" in question is the existence of alternate universes, so the most logical interpretation of your comment is that it is possible to test for the existence of an alternate universe.
There are a great many theories that are untestable and unfalsifiable. The existence of a God or a Creator is a hotly debated one, for instance.
Scientifically. No there aren't.
You're talking about hypotheses.
I think I know what you mean but if it's what I think you are doing a terrible job at explaining it. Theories in the scientific jargon are not the same as theories in the common parlance. What the commoner calls a "theory" is what we call a conjecture or an hypothesis. A theory in science is a summarization of experimental results, so if this is your take, I get your point.
I think I know what you mean, but using words like parlance and commoner makes you sound like a douche nozzle.
I'm sorry. I should have said muggles.
God is not a theory. There are no facts to support it and it has no predictive capabilities.
Evolution is a theory that demonstrates that species change via changes in genes. It is supported by facts and studies across multiple disciplines and has predictive capabilities.
One is science, the other is mythology.
There are some facts to support it, the problem is in the latter. Merely describing a system isn't sufficient, it's predicting more information. One can just as easily describe physics "as the things that are" but this doesn't let us find more information about the universe.
If your mathematical model tells you something should exist, doesn't that necessarily mean that it's something you can interact with, and thus measure given sufficiently advanced technology?
Perhaps but it's still not testable at that point.
Interestingly, parts of this universe are right now becoming unmeasurable, un observable, unfalsifiable to us even now. With dark energy propelling the expansion of space at an increasing rate, far-away regions of space can be moving away from us faster than light. This means they’re no longer part of our observable universe - we’ll never be able to reach them, see light from there, interact with these places in any way. Not the same universe anymore.
Someday living beings in the Milky Way might believe it’s the only galaxy that exists because no others will be observed. If one of them postulates that maybe there are all these other galaxies that are just out of reach - pinched off from our universe - in parallel universes you might say…. if someone says all that, it could also be just as handily dismissed.
In the most scientific way possible, there's no way these could affect our own. If they did, we'd consider that mechanism part of our universe. Real possibility - of course it's real. There's just absolutely no way to know, even if you made the question a lot more specific. (What does it mean, specifically? What would you expect to see if it were true vs false?)
As real as math
Max Tegmark came up with different "levels" of multiverse, and the first level only depends on the universe (not just observable) being infinitely large in volume - which as I understand it seems likely to be the case. (Certainly hasn't been ruled out at least)
Given infinite space with accompanying infinite matter/energy, there will be infinite repeats and near repeats of the stuff in any given volume of space - the volume of the observable universe for example, meaning us and everything we can interact with (even just see) is repeated infinite times, and with all physically possible variations.
And that's without any particular interpretation of quantum mechanics.
dang, cosmology is weird. I went to reply about the big bang, the age of the universe, and how it can't be infinite, but instead decided to look it up. I really don't understand this stuff.
Not everyone in this comment section uses correct nomenclature. It would be preferable for those bugged by it to use empathy to understand the true meaning of the comments (or, if impossible, to ask politely about the meaning) and to correct the mistakes in a nice way, avoiding the urge to take the wrong words litterally - that doesn't add to the discussion.
Hopefully that can be the case in one of the multiverses. I doubt it will be this one.
You mean I shouldn't react emotionally and impulsively because I disagree and feel personally offended by the first sentence in your comment?
Over the past decade or so he's been putting out papers with a model that's only a slight change to the standard model - that at the point of the big bang there was an expansion in both directions of time leading to a CPT symmetric universe.
He and his coauthors have managed to address a number of the major outstanding unsolved challenges in cosmology with only this theory, and are perhaps only a few years away from having some of its testable predictions verified. And at least one of the recent CERN projects that would have falsified the idea came up short just the other year.
If he lives long enough, he may well end up with a Nobel for his efforts.
It's probably my favorite bit of theoretical cosmology these days.
According to the many worlds interpretation of quantum physics there's not only alternative universes, but that there's an infinite amount of them including ones exactly like this one with just slight variations.
As in the classic ~theory~ idea, that each time a decision is made a new reality is created for each choice? For it to be possible would break our fundamental laws regarding conservation of mass and energy. Where would this alternative universe get all that energy and mass from? It’s possible our current understanding of the law is inaccurate, but it’s extremely unlikely.
why would alternative universes share a single source of energy? couldn't each have their own?
I’m thinking about the ~theory~ idea that involves a new universe being created every time a decision is made. Like if I flip a coin and get heads, another universe suddenly pops up where I got tails. It would need to create its own energy and mass out of nothing, which would break the laws of conservation.
I’m not super well versed in multiverse ~theories~ hypotheses though. It is slightly more probable that when our universe began existing, so did all the other alternative universes, in which case they would all have their own energy and mass. But then there would be essentially no chance that we would have alternative selves like in classic multiverse theories, since each universe would have started from the very beginning of time and evolved on its own path.
Edit: some wording
Just to play around with the idea: If we assume that an infinite number of universes were created at the moment of the Big Bang, and these only differ in random outcomes of quantum fluctuations, the would imply that there exist an alternate universe for every conceivable choice made, simply because there are infinitely many universes. They didn't appear when the choice was made, but they just happen to diverge from our own in some specific moment.
Hell, just presuming that the universe is infinite actually implies that there are an infinite number of "observable universes" outside our own observable universe. That in turn leads to the same result: If there is an infinite number of "observable universes" then there must be one universe that diverges from ours exactly ant the moment of every coin flip and every decision made.
Someone please tell me why I'm wrong, this hurt my head a bit.
This is all definitely getting to a point where it hurts my head too haha. My husband (a mathematician) has talked to me about the idea that infinite = every possible permutation of circumstances exists. Think about all the numbers between 0 and 1, it’s infinite. Now think about how many numbers exist between 0 and 2: also infinite, but also double the amount of infinite from 0 to 1. And all of those infinite numbers still exclude every other number that exists outside of the range of 0 to 2. So even if we do have infinite universes, that doesn’t necessarily mean there is a universe for every single tiny variation.
Hmm, I'm not sure about the first part there: For every number between 0 and 2, I can divide that number by 2 to get a unique number between 0 and 1, so there must be exactly the same amount of numbers in [0, 2] as in [0, 1]. By the same argument, for every number in [0, 1], I can multiply it by 2 to get a unique number in [0, 2]. Infinities are funny like that, but I'm not a mathematician, so there may be a hole in that argument.
From that, I don't see the argument that there wouldn't be a universe for every possible option. If there is an infinite number of universes, than for every possible random event (at the quantum scale if you will), the probability is 1 that any outcome happened in some universe, in fact every outcome should occur in an infinite number of universes. The probability that any two universes remain "aligned", or in the same state, decreases extremely rapidly of course, but that doesn't matter, because there are infinitely many of them, so an infinite number will always remain "aligned".
For example, if there are (right now) an infinite number of universes that are perfectly identical to ours, and I flip a coin, there will be infinitely many where it lands heads and infinitely many where it lands tails. If we follow that argument backwards, that for every random event there are an infinite number of universes experiencing every possible outcome, we'll get back to a moment in time where there were an infinite number of identical universes right after the Big Bang.
Wait, you lost me in the first part. For simplicity sake, let’s have two sets of numbers. Set A has the numbers 4, 5, and 6, a total of 3 whole numbers. Set B has the numbers 1 and 2, a total of 2 whole numbers. The number 4 from set A can be divided by 2, giving us the unique number 2 from set B. Set A and set B still have different amounts of numbers in them.
My husband is also chiming in, to simplify my original statement. Set C is [0, 1], an infinite range. Set D includes both [0, 1] and the number 2. Subtract set C from set D, you are left with just the number 2. Therefore, the number of elements in set D is exactly one larger than set C, even with both sets being infinite.
Now we're speaking the same language, I'll try to reformulate what I was saying.
Let's say you have the set [0,2], and I have the set [0, 1]. To check which is bigger, we play a "game" where you pick a number from your set, and I respond with a number from mine. Whoever runs out first has the smaller set. What I do, is that every time you say a number, I just divide it by two, and respond with what I get. That way, I can find a number in [0, 1] for every number in [0, 2], so [0, 1] can't be smaller. If we flip the situation, you can take whatever number I say, and multiply it by two to get a number in your set, so [0, 2] can't be smaller. Since none is smaller, they must be the exact same size.
Now I'm on thin ice, but I would love to know if there's an error in the following argument: We play the same "game", but now you have the set [0, 1] + {2}. For every number you say, I can still divide it by two to get a number in my set, so my set still isn't smaller. For every number I say you can:
Multiply it by two if it is in {1, 0.5, 0.25, ...}, i.e. a power of ½
reply with the same number otherwise
That way, you can get every number in your set from a number in mine, and opposite, so the set [0, 1] + {2} is the same size as the set [0, 1]. In other words, an uncountable infinity + 1 is the same size as it was before (might have something to do with the uncountable part).
I believe what we have done is create a bijection, that is: find a way to map every unique number in one set to a unique number in the other.
Okay, heads up that my husband and I are both sick right now and have a bit of brain fog, and he’s WFH while I have the day off so he can’t spare as much time to this. We see the logic in your argument and agree with your math. I’m trying to link this all back to the multiverse discussion so I can hopefully wrap my head around it.
Expanding on the idea that many universes were created in the Big Bang, I will pose a lot of questions that I don’t have answers to and will wrap up with a summary of possibilities.
Would the Big Bang create a finite or infinite number of universes? For there to be infinite universes, there would have had to be an infinite amount of mass and energy packed into a singular point before the Big Bang. Intuitively, and from my measly B.S. level of chemistry and physics classes, that feels wrong—but intuition, especially when it comes to infinities, is not worth much.
If there are an infinite number of universes, is this a countable or uncountable infinity (basically ℵ0 or ℵ1, I think)? Do we consider the number of all possible outcomes to be a countable or uncountable infinity?
Uncountable infinities are definitely larger than countable infinities. But are there different sizes of uncountable infinities? Your comment leads me to believe no, because we have no way of assigning a size to an uncountable number, but reading this article leads me to believe that there might be cardinalities beyond ℵ1. Your statements seem to agree with Woodin (and I think most of the math world at this point), while my idea of different sizes of infinities matches with Asperó and Schindler. If the top math minds of the world are this torn on the potential existence of different sizes of uncountable infinities, I can’t expect myself to understand it haha.
Summary of ideas:
My gut says that if we do somehow have multiverses then it must be a finite amount, and the possible number of outcomes is infinite (can’t decide if countable or uncountable)—therefore there can’t be a universe for every possible variation.
For there to be infinite universes that represent every possible permutation of events, I think we would be assuming that these are uncountable infinities, and that there is only one size of uncountable infinities (basically ℵ1 being the highest cardinality, I think).
If we say there are an infinite number of universes and an infinite number of possible outcomes, BUT there does not exist a universe that represents every possible outcome, this would rely 1 of 2 possibilities:
3a) the number of universes is a countable infinite while the number of possible outcomes is an uncountable infinite, or;
3b) that both the number of universes and the number of possible outcomes are both uncountable infinities, that the mathematical theory presented in the article above of different sizes of uncountable infinities (ℵ2 and beyond) is accurate, and therefore that the infinite number of possible outcomes is greater than the infinite number of universes.
I’ve tried writing out my thoughts several times and I keep erasing them, can’t keep track of how convoluted this is. I think I finally got it down though. Please tell me this isn’t complete nonsense lol, I need a nap
Haha, wow! Thanks for a really well thought out reply :) I think you nailed down where we were talking past each other, and I had no idea that the math world was divided on the sizes of uncountable infinities. Like you, I'm going to say that if the mathematicians are divided, I'm probably just going to accept that.
As for the "number of universes": I agree on the possible ways we could have multiple universes, without having one for every possibility. But I want to spin a bit back to what we mean by "multiple universes". I like the idea that if we assume that the universe is infinite, but we know that our observable universe is finite, that implies (without the assumption that "multiple universes" were created in the Big Bang) that there can be en infinite number of "observable universes" that fit within our infinite universe, that are simply moving so fast away from each other that they are completely separated (space between them is expanding faster that the speed of light).
That, in a way, leads back to one of your (our) questions: Does an infinite universe contain a countable or uncountable number of finite, observable, universes? Intuitively I would think the answer is "uncountable", just like there is an uncountable number of finite, non-overlapping intervals on the real numbers (I think?). That leads us back to your (our) other question/condition: Can uncountable infinities have different sizes? And like you said: If the mathematicians are divided on that, I'm not even going to try to answer.
So I don't think we'll get much further until the mathematicians conclude, but it's fun thinking about the possibilities :)
I also like the idea that these “other universes” might be within the realm of our infinite universe, beyond the reach of our finite observable universe. And I agree that we’ve probably reached as far as our logic can take us :) thanks for taking the time and effort to think this through with me, it was very fun!
Didn't our own universe create energy and mass out of nothing? Why couldn't others?
IIRC, our universe didn’t create mass and energy from nothing, it was all packed into an exceptionally small point in space and the energy was likely in a form completely unknown to us before the Big Bang. I can’t discount that there may be more of those densely packed points somewhere in the universe that could be used to form new universes. We can’t detect anything like that now, but that doesn’t mean it doesn’t exist.
I'm no expert either but I never got the idea of a new universe popping up everytime. Do other universes also cause popups of new universes or just ours? That'd escalate quickly :-)
I thought it goes that there's already infinite universes existing from the big bang on. Otherwise universes would be created without big bang. (The new universe would just pop up and you'd still believe it was created by the big bang but there never was one)
Also I'm not sure if laws of thermodynamics had to span accross universes. Take two theoretical perfect vacuum/radiation sealed boxes you put an energy source into. There's no way to communicate between boxes. Each box had it's own entropy and state of energy. Both would obey the laws of physics while being separate "systems".
That thought experiment wouldn't work, if new boxes had to pop up if one of the boxes wanted to.
Why would it need to create energy and mass out of nothing? Why are assuming the energy either comes from nothing or wasn't already there. Or better yet, that nothing as a source is a problem to begin with?
Conservation of energy applies to a universe. There are no such rules written out for imaginary multiversal mechanics. The "but mass and energy" thing gets thrown in the trash long before we reach this point, we stopped talking about matters of mass and energy two paragraphs ago. It's the same as asking "but why CAN you fly in your dreams? What about gravity, what happened to it?".
They don't exist. No one can prove otherwise yet. They're as bullshit as whatever we want them to be.
Where did all the energy in the universe come from? This is not physics, it's methaphysics. We are talking about things that are outside our knowledge and science is descriptive, not prescriptive. Extrapolations must be tested. This is not much different from saying that the most remote galaxies receding at speeds faster than light is impossible, because nothing can travel faster than light. Maybe it's just matter that can't break that rule, while space itself can expand at whatever speed, or maybe it's just an error somewhere in our assumptions. We still don't know. But we DO think they are receding faster than light.
That's not a very good example I don't think. I'm no cosmologist, but my understanding is that we know pretty well that distant celestial objects are moving away from us faster than the speed of light. Special relativity doesn't really say anything about non local objects, and the expansion of space does not violate locality. No information is being transmitted faster than the speed of light. The medium through which light is traveling is changing. It's not some big unsolved mystery.
I like Neil Degrasse Tyson's take on this one. At first we thought there was only one Sun, then we figured out the sun was a star, like so many others. Then we thought there was only one galaxy, then we figured there are much more than that.
Now we think there is only one universe, but it seems nature isn't very good at creating only one version of something. It's not unreasonable to think there are many universes. We just can't prove/observe it yet.
I honestly think that whatever soup we're all swimming in, it's just one big soup. There are not multiple soups. There are multiple solar systems and multiple galaxies within the soup, but it's just one big universe. We cannot fathom how big the universe is or if it's infinite or even if the universe is an infinitely massive sphere.
That's how I picture it. One big infinitely massive spherical universe.
But If it's infinite, how can it be a sphere?
I dunno, some things are too massive for us to comprehend.
I'm confused, are you saying there's only one solar system because we've only really named our planetary system the "solar system" ?
Not to be rude but that seems pedantic because there's more than one definition and according to Merriam Webster
solar system noun: the sun together with the group of celestial bodies that are held by its attraction and revolve around it also : a similar system centered on another star
Our solar system is just one specific planetary system—a star with planets orbiting around it. Our planetary system is the only one officially called “solar system,” but astronomers have discovered more than 3,200 other stars with planets orbiting them in our galaxy.
Genuinely curious to learn as I do not know a lot about this stuff and feel like I am missing something?
This is a case of a term that was until recently specific but is now becoming a more general term.
There are different levels of multiverse that are logically possible with our current understanding of physics.
It's incredible to think about.
In addition to what everyone else has already said, consider this: the "Universe" is by definition everything that exists. There cannot "be" things which do not exist. Therefore the question cannot be answered because it presupposes something could exist which is not part of the universe.
That's a philosophical answer, not a scientific one.
No, it's a logical answer. The definition of the word universe is "everything that exists"
Edit: this is really just another way of expressing that the hypothesis isn't testable. If something could be measured which could validate or falsify the hypothesis, then that thing being measured would have to exist, and therefore has to be part of the universe.
So a multiverse can't exist because it doesn't match a Webster's Dictionary definition or did you just not understand the question?
The question makes no sense because the terms aren't well-defined. It's like asking "are there other sets of integers besides the ones we know about?" There's only one set of all integers. We know what the integers are by definition. If something looks like an integer, it is an integer. Similarly, you can't ask about the existence of something which is not part of the universe, because if something exists, it is part of the universe.
The "Many Worlds" interpretation of quantum mechanics proposes that there are other universes separate from our own, perhaps even an incredible number of them if there's one for every quantum interaction.
It's consistent with our mathematical understanding of reality. But scientifically, it's still an open question on whether the hypothesis is testable or whether those other potential universes will ever be observable.
https://youtu.be/z-syaCoqkZA?si=5_KJB2rcscjhD9_e
As the others here are implying, the current consensus in the Physics community is that the many worlds hypothesis is not falsifiable, and so should be disregarded in favor of funding theories that can be proven or disproven. String theorists, the biggest proponents of the many worlds theory, are generally ostracized from greater physics academia since they have failed to produce any experimental designs to validate their claims for several decades after taking up a lot of tenured positions in the 90's, along with the "pop science" PR campaigning for their position that started then with some popular books and continues to this day in the works of Michio Kaku for example.
Relevant panels by leading physicists here: https://youtu.be/CNjckutR7BE?si=t88BigaInz01zamL
and here: https://youtu.be/eOvqJwgY8ow?si=5pbtgQqByJfi0Opi
Scientifically, we cannot yet talk about theories that are untestable and unfalsifiable. Sure, math or some other theory may imply other dimensions or parellel universes, but how will you measure one?
Would a ruler suffice?
Oof sorry. Gonna need a protractor.
That doesn't measure up for me.
Is that a tractor that lost its amateur status?
Yeah, he took a case of blueberry jam from the neighbor after he helped them out one day, plowing their fields while their Deere was broken down amd they waited for an expert to fly in from Portland.
Cost his team the championship. Forfieted the entire season.
Scientifically, there are no theories that are untestable and unfalsifiable.
How can you test/falsify the existence of something you can't interact with in any way?
Most likely you couldn't. But sometimes you can be aware of something (X) simply by seeing the effect it has on other things, even if you can't directly observe X. Think of Pluto, dark matter and dark energy; didn't/don't know what it is, but we know something is there.
My original comment was pointing out that a scientific theory is a framework that takes into account all the data. So something that is untestable and unfalsifiable definitionally could not be a theory. You'd be in hypothesis territory at best, but likely just conjecture.
Right, thanks for the clarification. Although in this context, the "theory" in question is the existence of alternate universes, so the most logical interpretation of your comment is that it is possible to test for the existence of an alternate universe.
There are a great many theories that are untestable and unfalsifiable. The existence of a God or a Creator is a hotly debated one, for instance.
Scientifically. No there aren't.
You're talking about hypotheses.
I think I know what you mean but if it's what I think you are doing a terrible job at explaining it. Theories in the scientific jargon are not the same as theories in the common parlance. What the commoner calls a "theory" is what we call a conjecture or an hypothesis. A theory in science is a summarization of experimental results, so if this is your take, I get your point.
I think I know what you mean, but using words like parlance and commoner makes you sound like a douche nozzle.
I'm sorry. I should have said muggles.
God is not a theory. There are no facts to support it and it has no predictive capabilities.
Evolution is a theory that demonstrates that species change via changes in genes. It is supported by facts and studies across multiple disciplines and has predictive capabilities.
One is science, the other is mythology.
There are some facts to support it, the problem is in the latter. Merely describing a system isn't sufficient, it's predicting more information. One can just as easily describe physics "as the things that are" but this doesn't let us find more information about the universe.
If your mathematical model tells you something should exist, doesn't that necessarily mean that it's something you can interact with, and thus measure given sufficiently advanced technology?
Perhaps but it's still not testable at that point.
Interestingly, parts of this universe are right now becoming unmeasurable, un observable, unfalsifiable to us even now. With dark energy propelling the expansion of space at an increasing rate, far-away regions of space can be moving away from us faster than light. This means they’re no longer part of our observable universe - we’ll never be able to reach them, see light from there, interact with these places in any way. Not the same universe anymore.
Someday living beings in the Milky Way might believe it’s the only galaxy that exists because no others will be observed. If one of them postulates that maybe there are all these other galaxies that are just out of reach - pinched off from our universe - in parallel universes you might say…. if someone says all that, it could also be just as handily dismissed.
In the most scientific way possible, there's no way these could affect our own. If they did, we'd consider that mechanism part of our universe. Real possibility - of course it's real. There's just absolutely no way to know, even if you made the question a lot more specific. (What does it mean, specifically? What would you expect to see if it were true vs false?)
As real as math
Max Tegmark came up with different "levels" of multiverse, and the first level only depends on the universe (not just observable) being infinitely large in volume - which as I understand it seems likely to be the case. (Certainly hasn't been ruled out at least)
Given infinite space with accompanying infinite matter/energy, there will be infinite repeats and near repeats of the stuff in any given volume of space - the volume of the observable universe for example, meaning us and everything we can interact with (even just see) is repeated infinite times, and with all physically possible variations.
And that's without any particular interpretation of quantum mechanics.
dang, cosmology is weird. I went to reply about the big bang, the age of the universe, and how it can't be infinite, but instead decided to look it up. I really don't understand this stuff.
Not everyone in this comment section uses correct nomenclature. It would be preferable for those bugged by it to use empathy to understand the true meaning of the comments (or, if impossible, to ask politely about the meaning) and to correct the mistakes in a nice way, avoiding the urge to take the wrong words litterally - that doesn't add to the discussion.
Hopefully that can be the case in one of the multiverses. I doubt it will be this one.
You mean I shouldn't react emotionally and impulsively because I disagree and feel personally offended by the first sentence in your comment?
You might enjoy this recent lecture from Neil Turok: https://youtu.be/rsI_HYtP6iU
Over the past decade or so he's been putting out papers with a model that's only a slight change to the standard model - that at the point of the big bang there was an expansion in both directions of time leading to a CPT symmetric universe.
He and his coauthors have managed to address a number of the major outstanding unsolved challenges in cosmology with only this theory, and are perhaps only a few years away from having some of its testable predictions verified. And at least one of the recent CERN projects that would have falsified the idea came up short just the other year.
If he lives long enough, he may well end up with a Nobel for his efforts.
It's probably my favorite bit of theoretical cosmology these days.
According to the many worlds interpretation of quantum physics there's not only alternative universes, but that there's an infinite amount of them including ones exactly like this one with just slight variations.
As in the classic ~theory~ idea, that each time a decision is made a new reality is created for each choice? For it to be possible would break our fundamental laws regarding conservation of mass and energy. Where would this alternative universe get all that energy and mass from? It’s possible our current understanding of the law is inaccurate, but it’s extremely unlikely.
why would alternative universes share a single source of energy? couldn't each have their own?
I’m thinking about the ~theory~ idea that involves a new universe being created every time a decision is made. Like if I flip a coin and get heads, another universe suddenly pops up where I got tails. It would need to create its own energy and mass out of nothing, which would break the laws of conservation.
I’m not super well versed in multiverse ~theories~ hypotheses though. It is slightly more probable that when our universe began existing, so did all the other alternative universes, in which case they would all have their own energy and mass. But then there would be essentially no chance that we would have alternative selves like in classic multiverse theories, since each universe would have started from the very beginning of time and evolved on its own path.
Edit: some wording
Just to play around with the idea: If we assume that an infinite number of universes were created at the moment of the Big Bang, and these only differ in random outcomes of quantum fluctuations, the would imply that there exist an alternate universe for every conceivable choice made, simply because there are infinitely many universes. They didn't appear when the choice was made, but they just happen to diverge from our own in some specific moment.
Hell, just presuming that the universe is infinite actually implies that there are an infinite number of "observable universes" outside our own observable universe. That in turn leads to the same result: If there is an infinite number of "observable universes" then there must be one universe that diverges from ours exactly ant the moment of every coin flip and every decision made.
Someone please tell me why I'm wrong, this hurt my head a bit.
This is all definitely getting to a point where it hurts my head too haha. My husband (a mathematician) has talked to me about the idea that infinite = every possible permutation of circumstances exists. Think about all the numbers between 0 and 1, it’s infinite. Now think about how many numbers exist between 0 and 2: also infinite, but also double the amount of infinite from 0 to 1. And all of those infinite numbers still exclude every other number that exists outside of the range of 0 to 2. So even if we do have infinite universes, that doesn’t necessarily mean there is a universe for every single tiny variation.
Hmm, I'm not sure about the first part there: For every number between 0 and 2, I can divide that number by 2 to get a unique number between 0 and 1, so there must be exactly the same amount of numbers in [0, 2] as in [0, 1]. By the same argument, for every number in [0, 1], I can multiply it by 2 to get a unique number in [0, 2]. Infinities are funny like that, but I'm not a mathematician, so there may be a hole in that argument.
From that, I don't see the argument that there wouldn't be a universe for every possible option. If there is an infinite number of universes, than for every possible random event (at the quantum scale if you will), the probability is 1 that any outcome happened in some universe, in fact every outcome should occur in an infinite number of universes. The probability that any two universes remain "aligned", or in the same state, decreases extremely rapidly of course, but that doesn't matter, because there are infinitely many of them, so an infinite number will always remain "aligned".
For example, if there are (right now) an infinite number of universes that are perfectly identical to ours, and I flip a coin, there will be infinitely many where it lands heads and infinitely many where it lands tails. If we follow that argument backwards, that for every random event there are an infinite number of universes experiencing every possible outcome, we'll get back to a moment in time where there were an infinite number of identical universes right after the Big Bang.
Wait, you lost me in the first part. For simplicity sake, let’s have two sets of numbers. Set A has the numbers 4, 5, and 6, a total of 3 whole numbers. Set B has the numbers 1 and 2, a total of 2 whole numbers. The number 4 from set A can be divided by 2, giving us the unique number 2 from set B. Set A and set B still have different amounts of numbers in them.
My husband is also chiming in, to simplify my original statement. Set C is [0, 1], an infinite range. Set D includes both [0, 1] and the number 2. Subtract set C from set D, you are left with just the number 2. Therefore, the number of elements in set D is exactly one larger than set C, even with both sets being infinite.
Now we're speaking the same language, I'll try to reformulate what I was saying.
Let's say you have the set [0,2], and I have the set [0, 1]. To check which is bigger, we play a "game" where you pick a number from your set, and I respond with a number from mine. Whoever runs out first has the smaller set. What I do, is that every time you say a number, I just divide it by two, and respond with what I get. That way, I can find a number in [0, 1] for every number in [0, 2], so [0, 1] can't be smaller. If we flip the situation, you can take whatever number I say, and multiply it by two to get a number in your set, so [0, 2] can't be smaller. Since none is smaller, they must be the exact same size.
Now I'm on thin ice, but I would love to know if there's an error in the following argument: We play the same "game", but now you have the set [0, 1] + {2}. For every number you say, I can still divide it by two to get a number in my set, so my set still isn't smaller. For every number I say you can:
Multiply it by two if it is in {1, 0.5, 0.25, ...}, i.e. a power of ½
reply with the same number otherwise
That way, you can get every number in your set from a number in mine, and opposite, so the set [0, 1] + {2} is the same size as the set [0, 1]. In other words, an uncountable infinity + 1 is the same size as it was before (might have something to do with the uncountable part).
I believe what we have done is create a bijection, that is: find a way to map every unique number in one set to a unique number in the other.
Okay, heads up that my husband and I are both sick right now and have a bit of brain fog, and he’s WFH while I have the day off so he can’t spare as much time to this. We see the logic in your argument and agree with your math. I’m trying to link this all back to the multiverse discussion so I can hopefully wrap my head around it.
Expanding on the idea that many universes were created in the Big Bang, I will pose a lot of questions that I don’t have answers to and will wrap up with a summary of possibilities.
Would the Big Bang create a finite or infinite number of universes? For there to be infinite universes, there would have had to be an infinite amount of mass and energy packed into a singular point before the Big Bang. Intuitively, and from my measly B.S. level of chemistry and physics classes, that feels wrong—but intuition, especially when it comes to infinities, is not worth much.
If there are an infinite number of universes, is this a countable or uncountable infinity (basically ℵ0 or ℵ1, I think)? Do we consider the number of all possible outcomes to be a countable or uncountable infinity?
Uncountable infinities are definitely larger than countable infinities. But are there different sizes of uncountable infinities? Your comment leads me to believe no, because we have no way of assigning a size to an uncountable number, but reading this article leads me to believe that there might be cardinalities beyond ℵ1. Your statements seem to agree with Woodin (and I think most of the math world at this point), while my idea of different sizes of infinities matches with Asperó and Schindler. If the top math minds of the world are this torn on the potential existence of different sizes of uncountable infinities, I can’t expect myself to understand it haha.
Summary of ideas:
My gut says that if we do somehow have multiverses then it must be a finite amount, and the possible number of outcomes is infinite (can’t decide if countable or uncountable)—therefore there can’t be a universe for every possible variation.
For there to be infinite universes that represent every possible permutation of events, I think we would be assuming that these are uncountable infinities, and that there is only one size of uncountable infinities (basically ℵ1 being the highest cardinality, I think).
If we say there are an infinite number of universes and an infinite number of possible outcomes, BUT there does not exist a universe that represents every possible outcome, this would rely 1 of 2 possibilities:
3a) the number of universes is a countable infinite while the number of possible outcomes is an uncountable infinite, or;
3b) that both the number of universes and the number of possible outcomes are both uncountable infinities, that the mathematical theory presented in the article above of different sizes of uncountable infinities (ℵ2 and beyond) is accurate, and therefore that the infinite number of possible outcomes is greater than the infinite number of universes.
I’ve tried writing out my thoughts several times and I keep erasing them, can’t keep track of how convoluted this is. I think I finally got it down though. Please tell me this isn’t complete nonsense lol, I need a nap
Haha, wow! Thanks for a really well thought out reply :) I think you nailed down where we were talking past each other, and I had no idea that the math world was divided on the sizes of uncountable infinities. Like you, I'm going to say that if the mathematicians are divided, I'm probably just going to accept that.
As for the "number of universes": I agree on the possible ways we could have multiple universes, without having one for every possibility. But I want to spin a bit back to what we mean by "multiple universes". I like the idea that if we assume that the universe is infinite, but we know that our observable universe is finite, that implies (without the assumption that "multiple universes" were created in the Big Bang) that there can be en infinite number of "observable universes" that fit within our infinite universe, that are simply moving so fast away from each other that they are completely separated (space between them is expanding faster that the speed of light).
That, in a way, leads back to one of your (our) questions: Does an infinite universe contain a countable or uncountable number of finite, observable, universes? Intuitively I would think the answer is "uncountable", just like there is an uncountable number of finite, non-overlapping intervals on the real numbers (I think?). That leads us back to your (our) other question/condition: Can uncountable infinities have different sizes? And like you said: If the mathematicians are divided on that, I'm not even going to try to answer.
So I don't think we'll get much further until the mathematicians conclude, but it's fun thinking about the possibilities :)
I also like the idea that these “other universes” might be within the realm of our infinite universe, beyond the reach of our finite observable universe. And I agree that we’ve probably reached as far as our logic can take us :) thanks for taking the time and effort to think this through with me, it was very fun!
Didn't our own universe create energy and mass out of nothing? Why couldn't others?
IIRC, our universe didn’t create mass and energy from nothing, it was all packed into an exceptionally small point in space and the energy was likely in a form completely unknown to us before the Big Bang. I can’t discount that there may be more of those densely packed points somewhere in the universe that could be used to form new universes. We can’t detect anything like that now, but that doesn’t mean it doesn’t exist.
I'm no expert either but I never got the idea of a new universe popping up everytime. Do other universes also cause popups of new universes or just ours? That'd escalate quickly :-)
I thought it goes that there's already infinite universes existing from the big bang on. Otherwise universes would be created without big bang. (The new universe would just pop up and you'd still believe it was created by the big bang but there never was one)
Also I'm not sure if laws of thermodynamics had to span accross universes. Take two theoretical perfect vacuum/radiation sealed boxes you put an energy source into. There's no way to communicate between boxes. Each box had it's own entropy and state of energy. Both would obey the laws of physics while being separate "systems".
That thought experiment wouldn't work, if new boxes had to pop up if one of the boxes wanted to.
Why would it need to create energy and mass out of nothing? Why are assuming the energy either comes from nothing or wasn't already there. Or better yet, that nothing as a source is a problem to begin with?
Conservation of energy applies to a universe. There are no such rules written out for imaginary multiversal mechanics. The "but mass and energy" thing gets thrown in the trash long before we reach this point, we stopped talking about matters of mass and energy two paragraphs ago. It's the same as asking "but why CAN you fly in your dreams? What about gravity, what happened to it?".
They don't exist. No one can prove otherwise yet. They're as bullshit as whatever we want them to be.
Where did all the energy in the universe come from? This is not physics, it's methaphysics. We are talking about things that are outside our knowledge and science is descriptive, not prescriptive. Extrapolations must be tested. This is not much different from saying that the most remote galaxies receding at speeds faster than light is impossible, because nothing can travel faster than light. Maybe it's just matter that can't break that rule, while space itself can expand at whatever speed, or maybe it's just an error somewhere in our assumptions. We still don't know. But we DO think they are receding faster than light.
That's not a very good example I don't think. I'm no cosmologist, but my understanding is that we know pretty well that distant celestial objects are moving away from us faster than the speed of light. Special relativity doesn't really say anything about non local objects, and the expansion of space does not violate locality. No information is being transmitted faster than the speed of light. The medium through which light is traveling is changing. It's not some big unsolved mystery.
This video from PBS Space Time is a good summary of the current state of science on this topic. https://youtu.be/z-syaCoqkZA?si=nRK78T_FAD5By-f0
I like Neil Degrasse Tyson's take on this one. At first we thought there was only one Sun, then we figured out the sun was a star, like so many others. Then we thought there was only one galaxy, then we figured there are much more than that.
Now we think there is only one universe, but it seems nature isn't very good at creating only one version of something. It's not unreasonable to think there are many universes. We just can't prove/observe it yet.
I honestly think that whatever soup we're all swimming in, it's just one big soup. There are not multiple soups. There are multiple solar systems and multiple galaxies within the soup, but it's just one big universe. We cannot fathom how big the universe is or if it's infinite or even if the universe is an infinitely massive sphere.
That's how I picture it. One big infinitely massive spherical universe.
But If it's infinite, how can it be a sphere?
I dunno, some things are too massive for us to comprehend.
There's only one solar system in the universe.
Reference: https://science.nasa.gov/solar-system/facts/
I'm confused, are you saying there's only one solar system because we've only really named our planetary system the "solar system" ?
Not to be rude but that seems pedantic because there's more than one definition and according to Merriam Webster
Meanwhile, elsewhere on the same site, over here https://spaceplace.nasa.gov/other-solar-systems/en/ says:
Genuinely curious to learn as I do not know a lot about this stuff and feel like I am missing something?
This is a case of a term that was until recently specific but is now becoming a more general term.
While planets orbiting other stars has been talked about for centuries, it is only in the past few decades that we have been able to confirm their existence.
So, up until then Solar system was a term that described our solar system as it was the only one known to exist.
There's only one solar system in the universe as it is the system of Sol (the Sun), our local star.
Other terms such as solar mass, solar wind, solar nebula, solar atmosphere, and solar flare likewise relate to Sol.
Yes, there's only one solar system in the universe as it is the system of Sol (the Sun), our local star.
Other terms such as solar mass, solar wind, solar nebula, solar atmosphere, and solar flare likewise relate to Sol.
https://youtu.be/1jmNzlTd09E?si=5w486YFlK4IbqpmK
Watch this^^^^^^
There are different levels of multiverse that are logically possible with our current understanding of physics.
It's incredible to think about.
In addition to what everyone else has already said, consider this: the "Universe" is by definition everything that exists. There cannot "be" things which do not exist. Therefore the question cannot be answered because it presupposes something could exist which is not part of the universe.
That's a philosophical answer, not a scientific one.
No, it's a logical answer. The definition of the word universe is "everything that exists"
Edit: this is really just another way of expressing that the hypothesis isn't testable. If something could be measured which could validate or falsify the hypothesis, then that thing being measured would have to exist, and therefore has to be part of the universe.
So a multiverse can't exist because it doesn't match a Webster's Dictionary definition or did you just not understand the question?
The question makes no sense because the terms aren't well-defined. It's like asking "are there other sets of integers besides the ones we know about?" There's only one set of all integers. We know what the integers are by definition. If something looks like an integer, it is an integer. Similarly, you can't ask about the existence of something which is not part of the universe, because if something exists, it is part of the universe.
The "Many Worlds" interpretation of quantum mechanics proposes that there are other universes separate from our own, perhaps even an incredible number of them if there's one for every quantum interaction.
It's consistent with our mathematical understanding of reality. But scientifically, it's still an open question on whether the hypothesis is testable or whether those other potential universes will ever be observable. https://youtu.be/z-syaCoqkZA?si=5_KJB2rcscjhD9_e