If we restarted the Universe n Times from T=0......

[Hybrid]

Would it always be identical?
Would it ever be identical?

Essentially with the current state of physics and taking quantum fluctuations into consideration, would it always be the same?

Is there motion at T=0?Another question:

If we restarted the Universe from the big bang and let it play out in accordance with Bohmian mechanics(or any other deterministic interpretation), would it then follow that everything would be exactly the same as it is now?
Or would it be different?

Apologies for the philosophical questions, but I'm wondering what modern physics has for an answer for this question specifically, and also what the majority of you think.

Thank you

 

[mathman]

My guess - quantum fluctuations would make things different.

 

[mfb]

Assuming you prepare the intial state in exactly the same way (no matter what exactly that means), it will depend on your favorite interpretation of quantum mechanics. In deterministic interpretations, it will be the same, in nondeterministic interpretations it will not (probably).

Is there motion at T=0?

I don't think that question is well-defined.

 

[Endan Rarity]

Well quantum fluctuations cause reality time field to disapparate. My best guess.

 

[phinds]

Well quantum fluctuations cause reality time field to disapparate. My best guess.

Uh ... what is a "reality time field"?

 

[tzimie]

In MWI it will be the same.

 

[Hybrid]

In MWI it will be the same.

Well MWI says nothing about the probability distribution of the evolution of the wave function in our own Universe. Just that all the possibilities within superposition do actually happen, just in other worlds.

So who's to say that each individual Universe isn't probabilistic(as quantum mechanics demonstrates), with all the possibilities eventually being actualized somewhere.

 

[mfb]

Well MWI says nothing about the probability distribution of the evolution of the wave function in our own Universe. Just that all the possibilities within superposition do actually happen, just in other worlds.

No, MWI gives you the amplitudes as well. In MWI that's all that exists. Same amplitudes => same universe.

So who's to say that each individual Universe isn't probabilistic(as quantum mechanics demonstrates)

Quantum mechanics demonstrates that some things appear indeterministic to observers that are part of the universe. That's perfectly compatible with a deterministic universe with MWI.

 

[Hybrid]

No, MWI gives you the amplitudes as well. In MWI that's all that exists. Same amplitudes => same universe.

So you can predict with 100% certainty the outcome of every wave function collapse?

Quantum mechanics demonstrates that some things appear indeterministic to observers that are part of the universe.

If it quacks like a duck, walks like a duck, and looks like a duck...

 

[mfb]

So you can predict with 100% certainty the outcome of every wave function collapse?

There is no wave function collapse in MWI.

If it quacks like a duck, walks like a duck, and looks like a duck...

So every object you observe at very dim light is black or grey just because you are unable to see its color?

 

[Hybrid]

There is no wave function collapse in MWI.

Yes I am aware of this, all possibities occur in a branching multiverse. Do you know objectively where every subatomic particle within a superposition will be located within our Universe before measurement? Do you know where it will end up, and what we will observe in our Universe, before measuring? No, you don't, because we only know the probablity distribution.

So every object you observe at very dim light is black or grey just because you are unable to see its color?

No it is an old metaphor. What I meant was if it appears to be probablistic, and experimentation yields results that lend credence to this. Perhaps it actually is indeterministic...rather than an infinite number of branching worlds with copies of everyone except one photon travels...a little to the right.

 

[mfb]

Do you know objectively where every subatomic particle within a superposition will be located within our Universe before measurement?

With infinite computing power, sure.

Do you know where it will end up, and what we will observe in our Universe, before measuring?

There is no such thing as "our universe", unless you mean the full universe with all worlds. Yes we can know where it will end up in this full universe.

No it is an old metaphor.

I know, and it is not applicable at all.

 

[Hybrid]

With infinite computing power, sure.

Could you elaborate a bit more on this?

There is no such thing as "our universe", unless you mean the full universe with all worlds. Yes we can know where it will end up in this full universe.

This assumes the MWI is correct, and let me redefine what I had said and substitute "our universe" with "our world".

I know, and it is not applicable at all.

That's a subjective statement in my humble opinion, and I feel as though what I wrote above holds up. However I can see why you would say that it doesn't apply here.

What I meant was if it appears to be probabilistic, and experimentation yields results that lend credence to this. Perhaps it actually is indeterministic...rather than an infinite number of branching worlds with copies of everyone except one photon travels...a little to the right.

Thanks for the interesting back and forth so far. What main reasons do you have for taking the MWI view, other than determinism, and perhaps getting rid of the wave function speculation?
How do you derive the born rule/probability with MWI?

Edited for clarification

 

[mfb]

Could you elaborate a bit more on this?

I don't know what would be left to elaborate. If you know the laws of physics, if they are deterministic, and know the initial state exactly, you can predict the evolution of the system. That is the definition of deterministic.

This assumes the MWI is correct

No, the whole discussion is in the context of MWI.
Also, we are talking about interpretations. "correct" is not a meaningful concept for interpretations. If I say "this tree is tall" and you say "it is small", who is correct? There is no objective definition of large and small - both are interpretations of "the tree has a height of 5 meters".

What main reasons do you have for taking the MWI view

tzimie and you started a discussion about MWI, I joined.

How do you derive the born rule/probability with MWI?

This is beyond the scope of this thread. We have multiple threads about the MWI, you can check those.

 

[Hybrid]

I don't know what would be left to elaborate. If you know the laws of physics, if they are deterministic, and know the initial state exactly, you can predict the evolution of the system. That is the definition of deterministic.
No, the whole discussion is in the context of MWI.
Also, we are talking about interpretations. "correct" is not a meaningful concept for interpretations. If I say "this tree is tall" and you say "it is small", who is correct? There is no objective definition of large and small - both are interpretations of "the tree has a height of 5 meters".
tzimie and you started a discussion about MWI, I joined.
This is beyond the scope of this thread. We have multiple threads about the MWI, you can check those.

What is your personally preferred interpretation of quantum mechanics?

Do you feel as though the Universe is deterministic or indeterminate?

Edit:

No, MWI gives you the amplitudes as well. In MWI that's all that exists. Same amplitudes => same universe.

Also I wanted to reiterate that by "universe" I had meant the MWI meaning of the word "world". In essence I was making the observation that MWI is only deterministic from a birds eye view, and makes no statement on how probabilities function within our individual world, and as such it would be best to say each individual world is indeterminate.

Thanks

 

[mfb]

What is your personally preferred interpretation of quantum mechanics?

I like MWI, it is simple and elegant.

Do you feel as though the Universe is deterministic or indeterminate?

That is philosophy, and I ignore philosophical discussions about the universe.

and makes no statement on how probabilities function within our individual world

There are no probabilities within a single world, because all measurements performed in the past have a certain outcome. People in this world can make theories about probabilities or amplitudes based on those observations.

 

[Hybrid]

There are no probabilities within a single world, because all measurements performed in the past have a certain outcome. People in this world can make theories about probabilities or amplitudes based on those observations.

I could see your point up until you said this; I believe this statement to be a complete non sequitur. This is the same thing as me turning it on it's head and simply declaring that because we cannot be sure of the outcomes of future measurements, and can only determine the probability before hand, the world is inherently indeterminate.Therefore people in this world can only make theories or interpretations about the deterministic nature of the amplitudes, based on our observation.

Not to get into a philosophical debate here or be outwardly tendentious, but you're being locally incoherent. To explain further that's like me saying because the 2007 New England Patriots lost the Superbowl, that they never had any chance to win in the first place. This is known as circular reasoning and this is inherently not a very scientific means of arriving at a non-biased conclusion. You're begging the question, so to speak. Many religious types perform this same fallacy when defending their "faith". You're basically saying that because the world is deterministic their are no probabilities.

Also the error here is MWI does not say the single world is deterministic, only the total structure is deterministic, because all possibilities happen, somewhere. It doesn't say where, or how it would work however, and is agnostic on that point, and to say otherwise is a logical fallacy in itself. So as I said before it is deterministic only from a birds eye view, MWI is not deterministic in the since that our individual world itself is as it cannot predict(doesn't say anything about) the outcomes of the probability distribution.

So I presume we can agree to disagree, unless you or someone else has something to add?

 

[mfb]

but you're being locally incoherent

I am not.

I also think this discussion gets pointless. Read the MWI threads if you are interested in the topic.

 

[Hybrid]

I am not..

No explanation as to why you feel that way?

I also think this discussion gets pointless. Read the MWI threads if you are interested in the topic.

I agree with you, and will do. Thanks again for the interesting discourse.

 

[Endan Rarity]

Uh ... what is a "reality time field"?

Something In progress and I meant to say reality field. Abstract quantum science. I,ll explain more later.

 

[Nugatory]

Something In progress and I meant to say reality field. Abstract quantum science. I,ll explain more later.

But please do be mindful of the PhysicsForums rule prohibiting speculative and personal theories that have not been published in an acceptable peer-reviewed journal...

 

[phinds]

Something In progress and I meant to say reality field. Abstract quantum science. I,ll explain more later.

If you do explain more later, take care that you are not violating the forum rules on personal theories.

 

[bahamagreen]

Endan Rarity, looks like the QEnergySpa folks use the phrase "quantum reality field"... hoping your explanation has something else in mind? :)

Mentor note: removed link (also in quote below)

 

[phinds]

Endan Rarity, looks like the QEnergySpa folks use the phrase "quantum reality field"... hoping your explanation has something else in mind? :)

AAAACCCKKK ! I do hope that's not what he has in mind.

 

[votingmachine]

Would it always be identical?
Would it ever be identical?

Essentially with the current state of physics and taking quantum fluctuations into consideration, would it always be the same?

Is there motion at T=0?Another question:

If we restarted the Universe from the big bang and let it play out in accordance with Bohmian mechanics(or any other deterministic interpretation), would it then follow that everything would be exactly the same as it is now?
Or would it be different?

Apologies for the philosophical questions, but I'm wondering what modern physics has for an answer for this question specifically, and also what the majority of you think.

Thank you

I don't think there is an answer. But what I THINK is no, it would be different every time. To be the same, there have to be deterministic rules for things that I don't think there are rules for. Radioactive decay, in particular seems to be inherently unpredictable. It is JMO, but, for example, while the total C14 population must decay at a certain rate, the clock for an individual atom seems probabilistic, not mechanistic. Vacuum energy would also seem inherently unpredictable.

If there is an exact, deterministic rule for everything, then the Universe would only depend on the starting conditions at T=0. And despite the complexity, it would always be exactly the same. I don't think that is the case, though that is JMO. So if you are counting/surveying, I vote "no".

 

[Hybrid]

I don't think there is an answer. But what I THINK is no, it would be different every time. To be the same, there have to be deterministic rules for things that I don't think there are rules for. Radioactive decay, in particular seems to be inherently unpredictable. It is JMO, but, for example, while the total C14 population must decay at a certain rate, the clock for an individual atom seems probabilistic, not mechanistic. Vacuum energy would also seem inherently unpredictable.

If there is an exact, deterministic rule for everything, then the Universe would only depend on the starting conditions at T=0. And despite the complexity, it would always be exactly the same. I don't think that is the case, though that is JMO. So if you are counting/surveying, I vote "no".

Based on my research being an autodidact by choice, I have come to the same conclusion. So I am inclined to agree with you, but I would also like to add to your response that this is also due to the indeterminate behavior exhibited by the probability amplitude in quantum physics.

I was trying to say on page one that even in the many-worlds interpretation you still have a probabilistic amplitude in any given individual world. MWI is only deterministic from a birds eye diorama-esque perspective, due to all possibilities actualized playing out over "time". Depending on the Hamiltonian, time may be fundamental or static/nonexistent. In addition the worlds postulated within the MWI combine and branch off into the future, and this action is essentially random. Given the "real time" splitting and recombining of the worlds/universes of the MWI, it would seem as though MWI requires the Hamiltonian be greater than 0 within the "multiverse", ergo time is fundamental.

Now if the Hamiltonian is zero this would seem to indicate some strange sort of conspiracy in the sense that all these quantum events, things like radioactive decay as you mentioned, vacuum energy, etc are "preset" to appear probabilistic, and/or random, but they wouldn't be, because if the multiverse is static and unchanging given the Hamiltonian is 0. Unless I am confused or misinterpreting something, somewhere, in which case I would greatly appreciate it if someone with more knowledge could correct me and point out where my misunderstanding is.

 

[mfb]

I don't think there is an answer. But what I THINK is no, it would be different every time. To be the same, there have to be deterministic rules for things that I don't think there are rules for. Radioactive decay, in particular seems to be inherently unpredictable. It is JMO, but, for example, while the total C14 population must decay at a certain rate, the clock for an individual atom seems probabilistic, not mechanistic. Vacuum energy would also seem inherently unpredictable.

If there is an exact, deterministic rule for everything, then the Universe would only depend on the starting conditions at T=0. And despite the complexity, it would always be exactly the same. I don't think that is the case, though that is JMO. So if you are counting/surveying, I vote "no".

As discussed before, there are deterministic interpretations of quantum mechanics.

I was trying to say on page one that even in the many-worlds interpretation you still have a probabilistic amplitude in any given individual world.

The amplitude is a well-defined number you can calculate.

it would seem as though MWI requires the Hamiltonian be greater than 0 within the "multiverse", ergo time is fundamental.

That doesn't make sense at all. Do you have a source for that claim?

 

[votingmachine]

As discussed before, there are deterministic interpretations of quantum mechanics.

Sure. But they are unproven. I understand there are deterministic positions and not-deterministic positions, and I gave mine. I must have missed something if the question required a proof of a system of laws that shows the Universe is deterministic. I cannot do that. I cannot even summarize all the available knowledge and theories. I took the question as an opinion poll.

Do you take the other position? I'm curious.

 

[Hybrid]

As discussed before, there are deterministic interpretations of quantum mechanics.

Yes and they're primarily MWI and Bohmian, the only others are time symmetric which could certainly be argued to be retro casual and as such, indeterminate or at the very least agnostic. As for many-minds, I consider that interpretation to bad pseudoscience(yes, I think there's good and bad pseudoscience), but a fun interpretation to think about none the less.

The amplitude is a well-defined number you can calculate.

Yes it is entirely deterministic in the sense that the probability amplitude is well defined. Second order differential equations with boundary conditions. The wave functions of the particles are determined, yes. However once you make a measurement for the location of the particle in relation to it's wave function it becomes probabilistic. In MWI there is no wave function, as everything happens(convenient), however in each individual world only one final objective measurement will be observed, and in that sense it is probabilistic within each individual world(universe), and only deterministic as a whole(the entire multiverse/many-worlds universe). I have no disagreement about the amplitude being well defined, I have a disagreement with statements claiming that the universe(or single world) is fully predetermined by initial conditions at t=0. When quantum mechanics is clearly probabilistic, among other things(random quantum fluctuations, radioactive atomic decay, the weather, etc). Anyway my point is at the end of the day each single world in MWI would be probabilistic.

That doesn't make sense at all. Do you have a source for that claim?

Just an observation I made while thinking about it, no specific source to speak of. There are a a few working MWI models and eternal inflationary models which are in contrast to this, for example: http://arxiv.org/pdf/1205.5550v2.pdf and http://arxiv.org/pdf/1104.2324v2.pdf

In that paper Yasunori Nomura builds a static multiverse model where the eigenvalue of the Hamiltonian is zero. However this still doesn't diminish what I said above about each world/universe being indeterminate throughout it's evolution, however the evolution of the quantum state of the entire multiverse is unitary and deterministic(as a whole). In his model you can take a selection condition at any moment in "time", which you interpret as t=0. You can then determine the state by solving the Schrodinger equation forward and backward in t. Albeit controversially he considers the eternally inflating multiverse and MWI to be one in the same.

Just to be sure I'm getting my point across I didn't mean to state that it must be that the MWI universe has to have a Hamiltonian greater than 0, only that it seems that way to me personally. As I said above in contrast to my perspective, I have offered an alternative idea.

Edit: In summary I agree in that the amplitude for the multiverse(in MWI) is well defined and you could predict anything as the evolution of the MW would be fully deterministic. However there is no means of knowing which branches will recombine and diverge/re-branch out into the future, and as such this would be random, along with vacuum energy fluctuations together adding credence to the idea that each world is still intrinsically indeterminate.

So as per my thread title I find the most likely answer to be "it would be different" rather than the same. Also MWI if you think about it logically is a gross violation of Occam's razor if you're talking about entities instead of laws.

 

[newjerseyrunner]

It's possible that the universe can be deterministic and given the exact same initial conditions but still end up different. There is no way to know if the universe is entirely self contained or if there are things outside of the universe that affect the universe. In some versions of string theory, gravity can leak out of one universe and end up in another one.

 

[mfb]

Sure. But they are unproven. I understand there are deterministic positions and not-deterministic positions, and I gave mine. I must have missed something if the question required a proof of a system of laws that shows the Universe is deterministic. I cannot do that. I cannot even summarize all the available knowledge and theories. I took the question as an opinion poll.

Do you take the other position? I'm curious.

You cannot prove interpretations. Actually, you cannot prove anything in physics. Interpretations of quantum mechanics are purely a matter of taste, as we cannot distinguish between them by experiments.

In MWI there is no wave function

Okay, sorry to be so direct, but this statement shows you have no idea about MWI. It is exactly the opposite: in MWI, the wave function is everything that exists.

 

[votingmachine]

Actually, you cannot prove anything in physics.

I disagree with this.

 

[Hybrid]

Okay, sorry to be so direct, but this statement shows you have no idea about MWI.
It is exactly the opposite: in MWI, the wave function is everything that exists.

No worries, direct is the way to communicate.
I am aware of that and had meant to say in MWI there is no wave function *collapse*. I'm surprised you hadn't realized this is what I meant.

 

[phinds]

I disagree with this.

Then you would do well to study the scientific method a bit more. Proofs are for math, not physics. It is a fundamental tenet of science that for a theory to be viable is has to be falsifiable, thus there is never a proof that it is true.

If you disagree with this, then please state a theory in physics that you believe to have been proven absolutely true.

 

[votingmachine]

Then you would do well to study the scientific method a bit more. Proofs are for math, not physics. It is a fundamental tenet of science that for a theory to be viable is has to be falsifiable, thus there is never a proof that it is true.

If you disagree with this, then please state a theory in physics that you believe to have been proven absolutely true.

I consider proving something false to be a proof. I understand theories and falsifiability. If I have a theory that heavier masses fall faster, you can prove that is wrong.

When you hold that proof is only to prove a positive you are making the word more limited than it is. The word "disprove" means to prove something is false. So a theory that has been proven absolutely true, is a false limitation. I can point to many that have been proven false.

 

[phinds]

I consider proving something false to be a proof.

Ah, well in that case I do understand your point of view. I don't agree w/ it but you are being logically consistent and making a reasonable argument given your premise. I don't think your point of view is one that is widely shared.

 

[newjerseyrunner]

I had to think about @mfb and @votingmachine's philosophies for a second. Pay attention to the capitalized words.

I agree that you can absolutely never prove that the mathematical description of the universe we've developed will ALWAYS work. It's not possible to do all experiments.

I agree that you can absolutely prove that the mathematical description of the universe we've developed will NOT ALWAYS work. We just need one test to violate it.

I can negate the first and say you can absolutely never prove that a description with ALWAYS NOT work.So I agreed with @mfb at first, but now I agree with @votingmachine. Science is about coming up with hypothesis and eliminating possibilities. Proofs are nice to show that math is consistent, but only way physics can advance is by eliminating possibilities, not proving them. There can be two equally mathematically valid equations for something only by elimination can you move forwards. I agree that proving what is not valid is in itself a form of proof, thought not the same kind that @mfb was originally referring to.

 

[votingmachine]

I thought it was just an oversight in the use of the word "prove". I did not think disagreeing to clarify the point was a deep philosophical point. I know we can't prove a theory true ... as you point out it is not possible to run an infinite variety of tests. And one contradictory test result proves that the model is not ubiquitously true, and is at the least, incomplete.

That really is just a semantic point. I am surprised that the opposite semantics was argued. I thought anyone reflecting on it would also see the proofs on the "disprove" side.

It isn't a big deal ... I thought I had the same semantics as everyone on this. I'll be careful with this word use in the future.

Inconceivable!

 

[Endan Rarity]

If you do explain more later, take care that you are not violating the forum rules on personal theories.

I will take care with that.

 

[Hybrid]

Inconceivable!

You keep using that word. I do not think it means what you think it means.

 

[phinds]

Inconceivable!

Good comeback. Love that movie !

 

[mfb]

@votingmachine: Okay, if you count "this is falsified" as "proof", then it is possible to make a proof. That was not the way I meant it in my post, and I thought that was obvious.

 

[votingmachine]

@votingmachine: Okay, if you count "this is falsified" as "proof", then it is possible to make a proof. That was not the way I meant it in my post, and I thought that was obvious.

I originally typed in my explanation the example that you can prove two masses don't fall at different rates, but I thought it was too much and deleted it. It was probably better to explain, but thought it sounded like I was a bit obsessive ... so then I sound obsessive later ... I understand what you meant, and what you meant is absolutely correct. I'm not actually quite as obsessive-compulsive as that explanation may sound.

 

[mfb]

I originally typed in my explanation the example that you can prove two masses don't fall at different rates

Can you? You can prove your two masses don't fall at different rates now and in your laboratory. What about tomorrow? What about other masses (different chemical composition, or antimatter)? What about repeating the experiment on Moon? You can do thousands of tests, at some point you are highly convinced that all known types of masses and probably unknown types as well fall at the same rate, but you cannot prove that it is true for all types of masses everywhere in space and time.

You can disprove the theory "all masses fall at the same rate" if you find a single counterexample. None was found so far (always assuming vacuum, absence of electromagnetic fields an so on of course).

 

[votingmachine]

Can you? You can prove your two masses don't fall at different rates now and in your laboratory. What about tomorrow? What about other masses (different chemical composition, or antimatter)? What about repeating the experiment on Moon? You can do thousands of tests, at some point you are highly convinced that all known types of masses and probably unknown types as well fall at the same rate, but you cannot prove that it is true for all types of masses everywhere in space and time.

You can disprove the theory "all masses fall at the same rate" if you find a single counterexample. None was found so far (always assuming vacuum, absence of electromagnetic fields an so on of course).

Hmmm. That makes sense. But it also a slight restatement of the "proof". The theory was that heavier masses fell faster. That was disproved. The new theory is that masses fall at the same rate ... it would be a rejection of science if you were to say that re-running the previous experiment exactly might give a different result. But that does not prove the new theory.

Hmmm. I admit the wording is puzzling me now. We can show that two different masses fall at the same rate (controlling all the interfering forces). That experimental result disproves a theory that predicts that heavier masses always fall faster. It does not prove affirmatively the theory that different masses have the same acceleration of gravity.

I'm just confused now. Previously I thought there was a clear proof of the falseness of one theory. But if that is worded as "proof" of the opposite theory ... then it seems wrong.

My model is that we can "prove" some things are false. But not that an open ended generalization is true. We know that the open ended generalization may break down under some conditions. I think that I might need to be more careful in my word selection. I still think there are things we can prove are not true, but those theories need to be quite specifically worded. Otherwise, it becomes an affirmation of the generalization on the other side.

You could be right. It might be better to simply say that nothing can be proven. Things can be known with great certainty, but not proven. I still have reservations about that position though. I'm sure you see the what I am saying ... I don't mean to beat a dead horse.

EDIT: I thought of an example. There was the logical theory that "all swans are white". But it was dis-proven by the discovery of a black swan. Now if you take the new theory to be "all swans are either black or white" ... then it is still not proven. But if the new theory is "swans are not always white", then it is proven (rather useless, but proven). I think there needs to be some caution around the wording of the new theory.

 

[phinds]

... But if the new theory is "swans are not always white", then it is proven (rather useless, but proven). I think there needs to be some caution around the wording of the new theory.

But here again, you are just proving a negative and I at least have already agree with you that you CAN prove a negative. But that is, as you say, pretty useless. It's proving a positive that you cannot do in physics.