# Does probability come from quantum physics?

(Phys.org)—Ever since Austrian scientist Erwin Schrodinger put his unfortunate cat in a box, his fellow physicists have been using something called quantum theory to explain and understand the nature of waves and particles.

But a new paper by physics professor Andreas Albrecht and graduate student Dan Phillips at the University of California, Davis, makes the case that these quantum fluctuations actually are responsible for the probability of all actions, with far-reaching implications for theories of the universe.

Quantum theory is a branch of theoretical physics that strives to understand and predict the properties and behavior of atoms and particles. Without it, we would not be able to build transistors and computers, for example. One aspect of the theory is that the precise properties of a particle are not determined until you observe them and "collapse the wave function" in physics parlance.

Schrodinger's famous thought experiment extends this idea to our scale. A cat is trapped in a box with a vial of poison that is released when a radioactive atom randomly decays. You cannot tell if the cat is alive or dead without opening the box. Schrodinger argued that until you open the box and look inside, the cat is neither alive nor dead but in an indeterminate state.

For many people, that is a tough concept to accept. But Albrecht says that, as a theoretical physicist, he concluded some years ago that this is how probability works at all scales, although until recently, he did not see it as something with a crucial impact on research. That changed with a 2009 paper by Don Page at the University of Alberta, Canada.

"I realized that how we think about quantum fluctuations and probability affects how we think about our theories of the universe," said Albrecht, a theoretical cosmologist.

One of the consequences of quantum fluctuations is that every collapsing wave function spits out different realities: one where the cat lives and one where it dies, for example. Reality as we experience it picks its way through this near-infinity of possible alternatives. Multiple universes could be embedded in a vast "multiverse" like so many pockets on a pool table.

There are basically two ways theorists have tried to approach the problem of adapting quantum physics to the "real world," Albrecht said: You can accept it and the reality of many worlds or multiple universes, or you can assume that there is something wrong or missing from the theory.

Albrecht falls firmly in the first camp.

"Our theories of cosmology say that quantum physics works across the universe," he said. For example, quantum fluctuations in the early universe explain why galaxies form as they did—a prediction that can be confirmed with direct observations.

The problem with multiple universes, Albrecht said, is that it if there are a huge number of different pocket universes, it becomes very hard to get simple answers to questions from quantum physics, such as the mass of a neutrino, an electrically neutral subatomic particle.

"Don Page showed that the quantum rules of probability simply cannot answer key questions in a large multiverse where we are not sure in which pocket universe we actually reside," Albrecht said.

One answer to this problem has been to add a new ingredient to the theory: a set of numbers that tells us the probability that we are in each pocket universe. This information can be combined with the quantum theory, and you can get your math (and your calculation of the mass of a neutrino) back on track.

Not so fast, say Albrecht and Phillips. While the probabilities assigned to each pocket universe may seem like just more of the usual thing, they are in fact a radical departure from everyday uses of probabilities because, unlike any other application of probability, these have already been shown to have no basis in the quantum theory.

"If all probability is really quantum theory, then it can't be done," Albrecht said. "Pocket universes are much, much more of a departure from current theory than people had assumed."

The paper is currently posted on the ArXiv.org preprint server and submitted for publication and has already stimulated considerable discussion, Albrecht said.

"It forces us to think about the different kinds of probability, which often get confused, and perhaps can help draw a line between them," he said.

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**More information:**albrecht.ucdavis.edu/

**Citation**: Does probability come from quantum physics? (2013, February 5) retrieved 18 June 2019 from https://phys.org/news/2013-02-probability-quantum-physics.html

## User comments

EyeNSteinTektrixAs it turns out, it all starts with water and polypeptides in your nervous system. Quantum uncertainty at that level introduces enough probability in molecular transport to evoke less-than-perfect physical prowess, which ultimately leads imprecise control of the energy required to repeatedly produce a perfect flip and snatch.

ValeriaTValeriaTWhydening GyreHe has, however, found a coin or two to flip...

kochevnikEyeNSteinaxemasterWOW! What a ridiculous statement! Many, many physicists accept the veracity of quantum theory but reject the idea of multiple universes. Multiple universe are NOT required by the theory, and are completely speculative! Whether or not other universes exist is a matter of philosophical OPINION. Moreover, the issue is unscientific in nature, since there's not even any way to test it!

You'd expect to hear this sort of thing on TV and among the general public, but from a physicist! Unbelievable!

ValeriaTkochevnikvacuum-mechanicsIt is interesting to note that up to now we still could not understand 'wave function of what, or what is wavy? Conventionally, it is just a mathematical abstraction; this is one real problem in quantum mechanics. Understanding the mechanism of quantum mechanics as below, could answer the problem.

http://www.vacuum...19〈=en

TektrixUnfortunately, this article is about probability and its origins, not quantum computing.

zorgTheGhostofOtto1923tiggerThe observer is as part of the system as anything else... there IS NO OBSERVER.

Yes, think about it... the human eye looking at something to observe is no different than photons interacting with a rock.

Interacting with matter... be it a rock, a magnetic field, a human eye... they are all the same, they all change the properties of the thing they are interacting with.

Why the continual, somewhat arrogant, fixation that the human body is a magical device that collapses waveforms into a reality? Is this because you think there is a 'soul'... some part of the human body that is outside the bounds of physics?

EikkaCollapsing the wavefunction also decides when the cat died.

Consider that at the moment of observation the cat exists in all possible states it can take while it is in the box, which includes all the possible histories, and all possible times of death.

The laws of quantum mechanism apply equally to what and where and when. The isotope that relases the poison by decaying is not in superposition only for decaying or not decaying, but when it decays if it does.

The cat knowing that it is alive is irrelevant, because nobody outside the box can read its mind telepathically.

ZackcbrodixAs for multiworlds, it is a question of whether we view time as a vector from a determined past into a probabilistic future, or the changing configuration of what is, that turns future probability into actuality. Consider this image; http://en.wikiped...film.svg

Do we view it as the present moving from left to right, or the frames moving right to left?

Before a race, there are many possible winners, but after it, only one.

StarGazer2011But this whole 'collapsing the waveform' or 'quantum uncertainty' seems to be mistaking ignorance for epiphany to me.

Ugh, if a phenomena requires an observer to be in a collapsed state, how did dinosaurs exist, or perhaps they didnt? Copenhagen taken to its extreme form seems to be sort of creationism to me, with the implicit assumption that before humans there was some sort of 'universal observer'.

VendicarEThe probability that the cat is dead or alive is identical - by the design of the experiment - as the probability that the radioactive source decays.

The state of the cat is only a macroscopic indicator of that decay.

The problem with the question of course, is not having a precise definition of probability that is devoid from connection with the real world.

The words "choice" or "selection" are part of the definition of probability and therefore make the definition dependent upon physical existence.

There can be no choice or selection without physical existence.

On the other hand defining probability without any physical connection seems to leave the definition simply a matter of creating a weighted set, and comparing the weight of one element with the weight of the set.

This certainly has no connection to quantum mechanics.

theonEikkaThe problem many people seem to be having with QM is that they interpret the word "observer" to mean a literal concious and cognitive observer.

What the word in QM means is simply the interchange of information. The superposition can only be in all states if no other thing depends on it being in a certain state. The classical world arises from these dependencies where A depends on B depends on C depends on... where each limits the possible states of the other according to the rules of physics until you're left with no wiggle room for the wavefunctions.

For that purpose, a rock can be the observer, and that is also the reason why Shrödingers cat has to be in a box so nothing else can interact with it until the box is opened. Quantum systems only behave in "weird" ways when you isolate them.

vlaaing peerdWhen you are able to count in all influencing factors one should be able to exactly predict the outcome of the flipping coin. Probably (no pun intended) the bigger the scale the less likely quantum scale probability would have influence on it.

rkolterI didn't see anyone really give you a full response. The whole point of the schroedinger cat is not to point out the absurdity of scaling up quantum effects to macro-scale objects. It is to provide a reference that is based in reality that surrounds us. For a LOT of people, it is far easier to understand "the cat is in an undetermined state" than it is to understand any explanation using waves and particles. The cat "experiment" was never meant to be taken seriously. When I explain it, I always end it with, "But in this case we know the cat is DEAD. Nobody poked air holes in the box..." You'd be surprised how often someone says, "Yeah if they poked air holes in we could see the cat..." And ta-da, a light goes off. :)

antialias_physorghttp://en.wikiped...s_friend

A rather more dramatic form can be achieved by placing a conscious observer (again Wiegner's friend) inside the box.

rkolterI don't know how you can say with certainty that randomness does not exist when you openly admit we do not know everything there is to know about physics. Simply put, what if the laws of physics include randomness? We have plenty of evidence of random events occuring. It seems more likely that random behaviour DOES exist, and we simply don't know why it exists. That question would then fall into a huge category of very interesting unknowns we can confirm, but do not fully understand yet.

antialias_physorgRadioactive decay would be one (of many) examples.

While you can fit curves to random processes (distributions) you cannot predict when an individual event will occur. Randomness is constrained - but it can be shown that it cannot be the result of smaller, fully deterministic processes. (such smaller processes would constitute 'hidden variables').

And by the Bell tests we have a strong argument that hidden variables do not exist. You could only save that with non-local hidden variables as in the deBrogli-Bohm interpretation of QM. But that opens up an entirely different box of problems.

And there is a strong indication that complete determinism isn't in the cards. (e.g. if you do double slit experiments with single electrons in the apparatus you still get interference patterns)

ValentiinroYou don't know how an atomic clock works.

http://en.wikiped...ic_clock

It has nothing to do with radioactive decay, which is random.

antialias_physorgOver many decay events you can average out - that's how we can use decay for measuring time (if there were few events then the dating via radiooactivity wouldn't work nearly as well).

It's like flipping a coin - you can't predict any one specific outcome, but over a million coin tosses you can map all the possible paths and see that the paths that lead to a near 50/50 split are VASTLY in the majority over those that are all heads - so betting on teh average outcome is better than betting on the extreme one.

I think you need to look up the difference between a probabilistic event and a probability distribution.

ValeriaTRoyaleI just have to say Tektrix, that this almost a goddamn PERFECT comment. I've reused it (with a reference) on Facebook, and about to add it to Google .

SethDDisproselyteBTW, the theory of scale relativity still gives the most elegant interpretation, but this is another sensitive argument.

antialias_physorgSince you can't control it to the quantum level that's a nonsensical approach. At the quantum level values aren't discrete but a probability distribution.

ValeriaTWhydening GyreI would say -

Probably...

Whydening GyreHumans knew that LONG before they thought it was flat...

VendicarE"We could determine the exact moment of the cats death. Unwitnessed." - Jalmy

VendicarEA coin toss can produce completely random results, and yet the statistical character of those tosses are absolutely predictable.

"The fact that these rates are measurable and can be generalized with a formula tells you that they are not random." - Jalmy

If Statistics wasn't predictable, then it would have no value.

Since it does, it is.

Since it is, you are wrong.

EyeNSteindaywalk3rIn the scope of CI QM, yes.

But what about out of it? What if QM does not = reality? Is it still all "random"? Because you said so? Because the Copenhagenists said so? Or just because the sky is blue?

What makes you so certain (that nothing is certain)? Isn't that allready a flawed logic construct to begin with?

The Bell experiments? There were no loophole-free Bell tests done yet. Double-slit? Without a truckload of fundamental assumptions, essentially inconclusive.. What else?

Nuclear decay? As random as a humans lifespan. While the average might converge to a certain value, it doesn't strictly dictate the path of an individual (which cannot be predicted without fully understanding the underlying principles and having sufficient data).

...

At this point, the only reasonable and honest conclusion that can be drawn is, that we can NOT be certain of either..

Ergo, WE SIMPLY DO NOT KNOW (yet).

rkolterYour whole point is wrong, then.

You can measure the probability of something happening with great accuracy. That does not mean that an individual event of that class is not random.

Since you say half-life is not random, consider carefully what half-life means. For a given sample of element X, 50% of the atoms in that sample will decay within the half-life. So if element X has a half-life of 10 minutes, some atoms will decay in 1 second. Some in 2 minutes. Some in 9 minutes and four seconds. Some in 15 minutes. Some in an hour...

You can say with great certainty that the half-life is 10 minutes. You can not say with any certainty when exactly a single atom (a single event) will decay. This is not because there are hidden variables we do not know about. It is because the decay is random.

daywalk3rI'm affraid it might be a bit more complicated..

There is no such thing as an absolute discrete coordinate either, as that would also require an absolute discrete point in time. And in the light of last several years of data, Planck time doesn't seem to fit that bill.

Everything is in constant motion, so every "discrete" coordinate is in essence just an average over a chosen time interval. No matter how sensitive/precise the measurements are, it will allways be like that. Sort of like the HUP in praxis.

In a certain sense, one could almost say that there is no such thing as a tangible NOW - just past, and future..

This actually makes all the arguments about discrete or probabilistic reality quite moot, as the ultimate answer seems to be neither, nor.

Whydening GyreAren't statistics and probability flip sides of the same coin?

rkolterI removed your personal attacks and snide comments to try to pull the core of your argument out of your rant.

At the core of your arguement is the assumption that "no pattern" means necessarily "no solution is more likely than any other". This is not the case. It is perfectly reasonable to have a process that is random, with some options more or less likely.

Also, you excluded the second definition from Webster:

(2) Relating to, having, or being elements or events with definite probability of occurrence

This is what we've been talking about.

TektrixRegardless of what you think, the authors of the article use this very example to illustrate the premise. And AP'org is right- the intrinsic nature of QM makes the levels of control you are suggesting, impossible. The idea that perfect knowledge lends perfect control is centuries old and has been firmly refuted by the huge body of work in QM.

thrakQ-StarYes, as long as you keep in mind that "statistics" only deals with things that have happened,,,, useful assessing causality.

Probability is the assessment of what might happen, once IT happens, it's no longer a probably event, it is an actual event with 100% probability (it happened.)

It is an important distinction.

antialias_physorgThat's why no one talks about computer generating random numbers but only about computers generating pseudo-random numbers.

They are numbers that are generated via an algorithm (and hence absolutely predictable since the next number depends on the previous one).

The difference with truly random events in real life is that they aren't dependent on each other (and again there are tests that can be used to distinguish whether events are indpenedent or not)

Whydening Gyredaywalk3rLite is a bot.

It has a blacklist of usernames, and continuously scours ALL articles in a predefined time interval. If it finds a comment by a blacklisted user, it automatically rates it with an assigned value (mostly 1).

As the bot is running on a server/computer, which runs off the electricity grid, and is connected to the internet through a multitude of devices (etc.), a fair bit of probability to its function still applies..

The admins who (should) manage this site seemingly don't give a damn about the comments sections, which in turn often gets pestered by spam, etc. So the next best thing in case the admins don't give a f***, is to give a s***.

Yea, I know, very on topic.. NOT! But who cares, eh? :-)

Whydening GyreInteresting coincidence, that...

If I didn't know better, I'd say it's my very competitive wife. However, she has to ask me how to use Word, so...

daywalk3rDoesn't matter. There is no such thing as 'perfect vacuum', neither is it possible to perfectly isolate any volume from the 'outside world' - no matter what you do, it will allways remain part of the whole/system.

Even passing an event horizon can not be strictly considered a causal disconnect (as often believed). What falls inside a BH does not dissapear, it becomes a contributing part of a bigger whole, which still affects the 'outside', be it either by gravity, resulting magnetic field(s), etc..

The only way how to achieve such 'disconnect' (on paper) is to define a threshold bellow which everything is considered negligible, or essentially non-existent. Well hello, I present to thee the magnifficient theory of QM..

When it comes to motion (or 'change') in a fundamental context, it can neither be considered absolutely discrete, nor truely random.

alaberdyMoebiusEyeNSteinantialias_physorgNo it is not. If it were you'd see as a result the combined results of the same experiment done twice, but with one slit occluded each time.

But instead you see an interference pattern.

EyeNSteinValeriaTIt's a simple clean logics, which is inaccessible for people, who are using the complex math. It's simply another hidden layer of reality for them. But the physicists and high-school teachers don't want you to use such a clean transparent logics, because they would lose their informational monopoly and social influence, if not job. Most of people want to understand the things as cleanly as possible and they resort to complex formal description of reality only when they don't see any other option.

ValeriaTWell, it just happens now. The world is changing - but the thinking of average people remains.

rkilburn81When we look out at all the galaxies, we are actually looking out past the boundry of our universe, like inside a marble looking out and space time bends in on itself, and so we are looking out at every possible Universe, every possible shape and fluctuation the big bang could have taken since the begining of time? Like waves of photons interacting, these island universes can also interact within the greater multiverse.

This might explain a lot.. Thoughts?

GPhillipGPhillipantialias_physorgIf that were the case they would fly through one slit or the other - because you could as easily put the screen at the slit (in which case you DON'T get an interference pattern)

But we DO see an interference pattern in the 2-slit experiment and hence they don't fly through either one slit or the other. So the 'dot' is not present until measured.

The photon is superimposed with itself because you get an interference pattern even if you space the photons so far apart that there is on average only one in the apparatus at any one time. (You can also do it with single electrons and get the same result)

GPhillipAs far as trying to explain paranormal phenomena with quantum effects, I'm afraid that is beyond the capabilities of the science. The scientific method requires experiments to be performed that can disprove the validity of a hypothesis.

GPhillipValeriaTValeriaTGPhillipMathematics addresses only a part of human experience. Much of human experience does not fall under science or mathematics but under the philosophy of value, including ethics, aesthetics, and political philosophy. To assert that the world can be explained via mathematics amounts to an act of faith.

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