B Why do scientists claim that there's true randomness?

[Karagoz]

When we look at the cars on the road, it appears like where they are driving is random, their directions appear as random. But the drivers don't drive into random directions. It appears random to us because we don't know the thoughts and intentions of the drivers. If we knew almost everything about the cars and the drivers (what they think, their intentions etc.) the cars' directions wouldn't appear to us as random.

Similar to dices; if we could compute almost everything about roll of the dices, we could calculate what the dices will show. And the roll of the dices wouldn't appear to us as random.

But in physics books it says that photons aren't like that. The randomness on whether they'll pass through the filters or not are true random. Even if we know everything about the photons, it'll still appear to us as random whether photons will pass through a filter or not.

In a Norwegian physics study book, it says "Even though we know everything we can know about the photons (direction of motion, frequency and direction of polarization), we can not say what happens to each photon when it hits the filter."

But how can scientists claim that they know everything that's possible to know about photons?

What if the photons have some more properties that could it make that not appear random anymore (properties that determine if a photon will pass through a filter or not), but just that these properties aren't discovered by the scientists yet?

 

[DrChinese]

... 1. But how can scientists claim that they know everything that's possible to know about photons?

2. What if the photons have some more properties that could it make that not appear random anymore (properties that determine if a photon will pass through a filter or not), but just that these properties aren't discovered by the scientists yet?

1. Not too many scientists are likely to express this point of view. There is much to be learned, papers are written every day on the subject.

2. Sure, there could be some as yet unknown explanation for apparent quantum randomness. In the meantime: it still looks completely random. And many things have been ruled out as being the source for the randomness. For instance, Bell's Theorem shows us it is not a local property of the photon.

 

[PeroK]

When we look at the cars on the road, it appears like where they are driving is random, their directions appear as random. But the drivers don't drive into random directions. It appears random to us because we don't know the thoughts and intentions of the drivers. If we knew almost everything about the cars and the drivers (what they think, their intentions etc.) the cars' directions wouldn't appear to us as random.

Let's say you take a point in a road. Somewhere in Norway perhaps. Let's say that at 10am (CET) on April 5th 2019 - or, perhaps 2029 - we are going to stand at that point and note that registration numbers of all the cars that pass by for 1 hour, say.

Now, what information would you need to correctly predict that?

Is that really determinable? Or, is that theorectically unpredictable? With enough information, would you be able to say with certainty precisely which cars pass that point 1 year (or 11 years from now)? Or, even with all possible information, would you only be able to give a probability for each car registration?

 

[Khashishi]

What if the photons have some more properties that could it make that not appear random anymore (properties that determine if a photon will pass through a filter or not), but just that these properties aren't discovered by the scientists yet?

What you are describing is a called a hidden variable theory, which has been questioned at various times https://en.wikipedia.org/wiki/Hidden_variable_theory
For example, Bohmian pilot wave theory is a hidden variable theory which is deterministic.

However, generally, in science, we don't like to include things in our theory that we have no way of measuring. They may as well not exist, by Occam's razor. There isn't any way to measure the Bohmian pilot wave, other than from the result of the measurement that the Bohmian mechanics are supposed to explain. Since we know no way to measure it, it might as well be random. But there is no way to prove it.

 

[DaveC426913]

In a Norwegian physics study book, it says "Even though we know everything we can know about the photons (direction of motion, frequency and direction of polarization), we can not say what happens to each photon when it hits the filter."

But how can scientists claim that they know everything that's possible to know about photons?

What if the photons have some more properties that could it make that not appear random anymore (properties that determine if a photon will pass through a filter or not), but just that these properties aren't discovered by the scientists yet?

You want to read up on Bell's Hidden Variables Theorem.
It essentially shows that, if the photons had some hidden variables, we would not get the results we observe.

 

[StevieTNZ]

You can be nick-picky and question the "assumption" that other people have thoughts etc of their own, as an example. Philosophy is allowed here when mentors permit so. Of course I don't live life like no one has no independent thoughts and actions.

To clarify DaveC's comment, "if the photons had some hidden variables, we would not get the results we observe", there is always still Bohmian Mechanics which, that I am aware, is currently unable to be experimentally verified, to give a different result to standard QM.

 

[PeterDonis]

What if the photons have some more properties that could it make that not appear random anymore (properties that determine if a photon will pass through a filter or not), but just that these properties aren't discovered by the scientists yet?

The answer, based on Bell's Theorem, and experimental tests showing that quantum objects like photons violate the Bell inequalities, is that if such properties exist, they must be very strange compared to our ordinary intuitions: they can't be the kind of local realistic properties that underlie the other examples you give.

You want to read up on Bell's Hidden Variables Theorem.
It essentially shows that, if the photons had some hidden variables, we would not get the results we observe.

More precisely, it shows that, if the photons had hidden variables that satisfy the postulates used to derive the Bell inequalities, we would not get the results we observe. It is still possible that hidden variables could exist that violate those postulates; but as noted above, such hidden variables would be very strange compared to our ordinary intuitions.

Bohmian Mechanics which, that I am aware, is currently unable to be experimentally verified, to give a different result to standard QM.

Bohmian mechanics is an example of a "hidden variable" model that can violate the Bell inequalities (which it must since it makes all of the same predictions as standard QM). The hidden variables are unknown and unmeasurable positions of quantum objects; but the equation of motion of these variables is highly nonlocal since it includes the quantum potential. (Also, AFAIK there is no known consistent relativistic formulation of Bohmian mechanics.)

 

[Nugatory]

We've pretty much answered the original question here. Several posters have suggested that @Karagoz look into Bell's theorem, and all I can add that is that our own @DrChinese maintains a web page that would be a good starting point.

This thread is closed. If looking at Bell's theorem leads to new questions, than we can have new threads - but please please please look at the eighty-three megabazillion threads we already have first.