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Author Topic:   Have quantum interpretations been experimentally verified?
Son Goku
Member
Posts: 1101
From: Ireland
Joined: 07-16-2005


(1)
Message 46 of 50 (826386)
12-29-2017 4:28 PM
Reply to: Message 43 by Phat
12-20-2017 9:39 AM


Re: The Cosmic Toothpaste Tube
Hi Phat,

Sorry for the delay, busy with the family at Christmas.

Explain to me in a nutshell the prevailing theories on the concept of multiverses.

So in a nutshell, there's really only two. They're not competing in any way, both could be true, as they deal with separate issues.

The First:
In Quantum Mechanics we have the Many-Worlds interpretation. In brief, unlike most theories of physics, the maths of quantum mechanics doesn't come with a clear mental picture of what is going on. So there are several "narratives" people use to picture the maths mentally. Many-Worlds is one such.

It basically says the universe has several parallel timelines. In one timeline an atom decayed, in another it didn't. Two separate histories. Now in science fiction this is usually presented as "every possibility" occurs, but that isn't true, only a small range of histories are possible and most don't differ all that much. I can say more about this, but it becomes a bit technical, keeping in mind having a nutshell answer.

The Second:
Genuinely different universes with totally different laws. Maybe a world with ten dimensions and nine forces, rather than four dimensions and four forces like ours. Worlds where gravity works differently so that things spin when they fall. Places where relativity isn't true. Totally different worlds. Some theories of particle physics suggest this. In most models of this conjecture there are a lot of such different universes.

Again, both could be true. Our universe might have several timelines and there could be separate universes as well.

Are they realistically plausible?

The first type (multiple timelines) has no evidence against it yet, despite some attempts to falsify it. However all the evidence can still be explained by orthodox versions of Quantum Mechanics, so the jury is out. In other words, it makes predictions we can verify and those predictions hold up, but other ways of looking at Quantum Mechanics also make those predictions, so hard to know.

The second type has no strong evidence in its favour, but we're not advanced enough to perform the necessary experiments. It's the kind of thing that may need to wait until we colonise space.

Could we hypothetically exist in multiple dimensions?

I'm taking this to mean "does the universe we live in possibly have more than four dimensions?" So far the evidence is strongly against this, we seem to exist in a four dimensional reality. Predictions of theories with more than four dimensions have been shown to be wrong.

How does a mathematician connect the hypothetical to reality?

For the different universes or multiple dimensions theories the connection takes one of two forms.

They predict something about particles, e.g. an extra species or maybe a change in how they collide with each other. For example if we live in four dimensions photons flying toward each other bounce off each other 0.00012% of the time, but if there is a hidden fifth dimension they bounce off each other 0.00027% of the time.

Or they predict something about the heat signature of the big bang, e.g. if there are other universes out there, the should have affected the big bang and the cold patches in the big bangs after glow should be 0.0045% cooler than they would be otherwise.

For the multiple timeline theories, going into the way you connect it to reality would go outside the nutshell scope, it's a technical enough topic.


This message is a reply to:
 Message 43 by Phat, posted 12-20-2017 9:39 AM Phat has acknowledged this reply

  
Son Goku
Member
Posts: 1101
From: Ireland
Joined: 07-16-2005


(3)
Message 47 of 50 (830639)
04-04-2018 2:48 PM


Quantum Mechanics Basically I
I've been thinking over the past few months how to express the essential mystery of quantum mechanics. As a result here is the briefest simplest version I can give. I've decided to cut all technical minutia and focus on the core issues in three short posts. This one is about the main issue with understanding Quantum Mechanics.

The Main Issue:
The basic problem with Quantum Mechanics is that it doesn't really seem to be "about" anything.

In the mathematics of Newtonian Physics you can point to terms in the equations and say, oh that's a force, that's momentum, that's the position of the particle, etc
Even the solutions of equations have an obvious meaning, i.e. this is the path the object will take.

In General Relativity it's the same. Yes it might discuss spacetime and four-dimensional curvature, these are abstract and strange. However it is still a narrative about entities changing and developing, they just happen to be very abstract entities.

Quantum Mechanics on the other hand is only "about" probabilities to see results. It just says "in such and such a circumstance when you have equipment set up in a particular way, you have the following chance of seeing this value for that quantity". However it doesn't say how things get those values. It's sometimes not even clear that the values are really a property of the object in question, an atom let's say, or just something you get when your equipment interacts with an atom.

It's not even really clear if an electron is actually an object in quantum mechanics, or just a bunch of probabilities arranged in a certain way, i.e. in certain experiments with equipment arranged a certain way you have a high chance of detecting charge concentrated around a point. However it's not clear that's actually due to you finding a small object with a charge, or is it just something that happens to your equipment in those situations.

This is not just philosophical musing, quantum mechanics itself is genuinely unclear about which is the case.

The following is additional and provided because I have noticed it helps some, but others find it confusing. If it is the latter for you, just ignore:
Julian Schwinger in his book "The symbolism of atomic measurement" and Giacomo Mauro D’Ariano in "Quantum Theory from First Principles: An Informational Approach" both derive Quantum Mechanics from first principles as a theory of how a rational agent might assign chances to experimental outcomes, without basically any insight from physics. D'Ariano in particular essentially derives it as the most general mathematical theory of "learning", i.e. updating your knowledge of the world.
This provides a clearer picture of the problem to some. What are you learning about? Just experimental results and how "bet on them", or something genuine about the world?


Replies to this message:
 Message 49 by Phat, posted 04-18-2018 12:02 PM Son Goku has responded

  
Son Goku
Member
Posts: 1101
From: Ireland
Joined: 07-16-2005


(1)
Message 48 of 50 (831152)
04-13-2018 8:10 AM


So continuing on, what is difficult when you try to make sense of QM? What aspects make it difficult to see what QM is about?

I realised three posts wasn't going to cut it, but I'm still trying to keep things brief! Apologies!

A brief sketch of QM mathematically will help.

Quantum Mechanics describes the current state of the world as a set of amplitudes. Amplitudes are numbers that when you square them, they give the probability of some event occurring. Right now, since I'm not giving anything an interpretation, that's all they are.

So there's an amplitude for anything of the form:
Amplitude to see quantity A in region R have value V at time period T .

A concrete case would be:
Amplitude to see the Voltage in this wire be 4.5V between 10:40 and 10:50.

QM might give this an amplitude of -0.2, squaring makes it 0.04. So that's a 4% chance of this happening.

Just note that the amplitudes can be negative, however since we square them to get the probabilities, the probabilities won't be.

The final component is the uncertainty principle. Most quantities come in pairs, like position and moment, voltage and electric potential. When the amplitudes for one are concentrated around one value, meaning that outcome is very likely, the probabilities for the other become more spread out and uniform. Or put another way, as one element of the pair becomes more certain, the other becomes more random. Such pairs are called conjugate variables.

With this in place, I'll begin a list of problems, spread over some posts, before ending with interpretations.

1. What's a particle?


So QM presents a very detached and almost totally observation based picture of a particle. It is simply the case that there are certain "states of the world", that is lists of amplitudes, where a set of quantities co-occur (abstract, but just wait).

So an electron is just a case where the amplitudes say certain equipment will always detect a bit of spin with a bit of electric charge. To then conclude that there is an object, like a little ball, that travels around holding those properties is a mental picture that QM doesn't give any particular support to. This will get more extreme in the two cases below.

The silver oven: Let's say I've set up an oven that burns silver and I build a piece of equipment that can detect spin and charge. I then notice the oven makes the detector click every 30 seconds. So I say I have detected an electron, which the oven produces at a rate of one every 30 seconds. My detector is sensitive enough to narrow the location of the clicks down to the nanometer.

Now, without touching the oven, I go off and get a new detector that can narrow the clicks down to the femtometer and position it outside the oven. So I will continue to get clicks every thirty seconds, but sometimes it will be three clicks. Two with negative electric charge and one with positive. In a particle based view, I have seen two electrons and one positron.

Why though? The oven creating the particles hasn't changed, I've just made the equipment finer in resolution. Now the normal intuitive explanation is that the equipment, by probing so deeply, provided the energy to create the particles, but QM is silent on this. In fact it always presents there being a nonzero amplitude to detect three clicks in a femtometer sized region. The previous equipment just didn't have access to regions of that size, but QM always said the possibility was there.

So what is the oven actually emitting. It's hard not to conclude that its just "some charge and some spin" which will be packaged as single or multiple clicks depending on your equipment.

The beam of light:
Take a beam of light. The conjugate variables in the case of light is colour(frequency) and photon number. Hence the higher the probability for the light to be a single colour, the more spread out its probabilities are for photon number. This can be tested with Laser light. Lasers are states of the electromagnetic field that are highly likely to be observed having only one consistent colour. Consequently when you place a photon detector in front of them they have an equal likelihood of producing several values. The exact same beam of laser light could be measured as containing 10 photons one minute and 1000 the next.

Again how many particles are there? Is the possible conclusion that there is no such thing, simply probabilities for clicks?

Similar "uncertain particle count" occurs in all quantum mechanical system of sufficient complexity, for example most atomic nuclei have an indeterminate number of pions inside them. So to what extend can we say what anything is "made of", if particle count isn't fixed?

Ending on a brief point, even Hydrogen in QM is just a state with a set of amplitudes that "often" act like those of a proton combined with those of an electron. However some of the amplitudes for hydrogen events can't be parsed as a combination of those for a proton or an electron. So to what extend is it made of a proton and electron?

2. Interference:


In Quantum Mechanics possibilities can interfere. (If the mathematics below is tedious, skip to the bolded point)

Consider betting on a horse to come in various positions in a race, say 1st, 2nd, 3rd in a three horse race. The horse can be fed either Smithson horse food or Johnson horse food.

In the first case his chances of coming in the various positions are:
(0.1,0.4,0.5)

i.e. 10% chance of coming first.

In the second case:
(0.2,0.4,0.4)

If you don't know which of the brands of food the horse takes, you can combine the above to get:
(0.15,0.4,0.45)

So a 15% chance of winning when you aren't sure of which brand he took.

However in the QM case, since amplitudes can be negative, we could have for the first case:
(0.316,-0.632,0.707)

and for the second:
(0.447,0.632,0.632)

I won't go into how these are combined when the horse could eat either brand of food, but the main point is that the second possibility would cancel out due to the minus signs.

Hence a quantum horse has a chance of coming second if he eats one brand, a different chance of coming second when he eats another brand, but if he could eat either brand he has no chance of coming second at all. It is possible for an outcome to cancel out from two different sets of possibilities,even though it is possible in each of them alone.

This is why the double slit experiment is confusing. There are points on the detection screen that have a chance of being lit up when either slit is open, but not when both are open, because the two events of "particle goes through right slit and hits point A" and "particle goes through left slit and hits point A" have their probabilities cancel out.

If you see the probabilities as purely a reflection of your knowledge, it is very hard to see how this is possible. How by not knowing a binary outcome (Horse food A or B) do I remove something that can happen under either outcome?

It also leads to the next confusion....

Edited by Son Goku, : Bolding and spelling

Edited by Son Goku, : No reason given.

Edited by Son Goku, : No reason given.


  
Phat
Member
Posts: 10656
From: Denver,Colorado USA
Joined: 12-30-2003
Member Rating: 1.4


Message 49 of 50 (831471)
04-18-2018 12:02 PM
Reply to: Message 47 by Son Goku
04-04-2018 2:48 PM


Is curiosity the primary motivation?
Son Goku writes:

The basic problem with Quantum Mechanics is that it doesn't really seem to be "about" anything.

One question which I have regarding the motivation to study and research this stuff is what motivates you to do it? (Thank God that you do, because we wouldn't be where we are as a species without folks such as you!)

Chance as a real force is a myth. It has no basis in reality and no place in scientific inquiry. For science and philosophy to continue to advance in knowledge, chance must be demythologized once and for all. –RC Sproul
"A lie can travel half way around the world while the truth is putting on its shoes." –Mark Twain "
~"If that's not sufficient for you go soak your head."~Faith
Paul was probably SO soaked in prayer nobody else has ever equaled him.~Faith :)

This message is a reply to:
 Message 47 by Son Goku, posted 04-04-2018 2:48 PM Son Goku has responded

Replies to this message:
 Message 50 by Son Goku, posted 04-19-2018 5:44 PM Phat has not yet responded

  
Son Goku
Member
Posts: 1101
From: Ireland
Joined: 07-16-2005


Message 50 of 50 (831519)
04-19-2018 5:44 PM
Reply to: Message 49 by Phat
04-18-2018 12:02 PM


Re: Is curiosity the primary motivation?
I've nothing profound to offer on that point unfortunately. I'm motivated to study it the same way I'm motivated to play sports, swim or read fantasy. I just like it. When I hear something from it I just want to know more.
This message is a reply to:
 Message 49 by Phat, posted 04-18-2018 12:02 PM Phat has not yet responded

  
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