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#54551 10/21/15 03:20 PM
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Bill S. Offline OP
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The question as to whether or not QM requires a universal time seems to come and go without any real resolution.

Does that mean that there is not a clear answer?


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The more I look at it, the worse it gets!

It begins to look as though non-relativistic QM requires a universal time, but relativistic QM certainly doesn't.

That can't possibly mean that the same scenario calculated using relativistic and non-relativistic QM would give different answers, and that they would both be right; or could it?


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Originally Posted By: Bill S.
The more I look at it, the worse it gets!

It begins to look as though non-relativistic QM requires a universal time, but relativistic QM certainly doesn't.

That can't possibly mean that the same scenario calculated using relativistic and non-relativistic QM would give different answers, and that they would both be right; or could it?

Non relativistic QM is like classical physics it can give wrong answers when given a problem it can't answer smile

This is sort of along the lines Lubos recently berated someone of the physics forum over
http://motls.blogspot.com.au/2015/10/quantum-field-theory-obeys-all.html

Quote:
As far as you think that the Hilbert space of a QFT is something "very different" from the Hilbert space of non-relativistic quantum mechanics describing the same or similar physical system, you must have completely misunderstood something essential about at least one of these theories. In reality, the non-relativistic QM is a limit, the non-relativistic limit, of QFT.

QM and QFT are not different and will never give different answers if used properly. What you can do is misuse it.

What you have done is the same as that forum poster, the error is in your first assumption.

Ergo that non-relativistic QM can tell you anything about time.

If I ignore friction apparently all bodies move forever .... same thing as what you just did smile

Now I reach the same conclusions about this rubbish as Lumo this is a teaching issue
Quote:
Maybe the reduction of quantum field theory – e.g. a Dirac field – to the non-relativistic quantum mechanics in the v<<c limit isn't sufficiently well explained in the basic courses of QFT if it is explained at all.

Bluntly there isn't an issue one is a simplification and don't go outside the simplification.

You will get sharp rebukes for that sort of question on physics forums because the anti-quantum
zealots try to pick up an perceived disagreement within QM real or imaginary.

Last edited by Orac; 10/22/15 04:49 AM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
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http://motls.blogspot.com.au/2015/10/quantum-field-theory-obeys-all.html
1. Classical physics
2. Quantum mechanics
3. There is simply not third way.
Originally Posted By: Orac
Non relativistic QM is like classical physics it can give wrong answers when given a problem it can't answer

Quote:
QM and QFT are not different and will never give different answers if used properly. What you can do is misuse it.

What you have done is the same as that forum poster, the error is in your first assumption.

Ergo that non-relativistic QM can tell you anything about time.

It has taken me a long time to get round to reading Motl’s blog, and I probably need clarification as to what he and you are saying.

Is it something like: QM and QFT are the same thing, and will always give the same answers, as long as you don’t ask QM the wrong questions?


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Originally Posted By: Bill S.
Is it something like: QM and QFT are the same thing, and will always give the same answers, as long as you don’t ask QM the wrong questions?

More along the lines that QFT is a subset of QM and can not give different answers. If you think that QFT and QM don't say the same thing then you are in error because as the mathematics reduces to exactly the same thing.

QM was the historic generic version but as we understood fields in particular physics we were able to turn the QM into a more controlled subset of the field interactions.

In most of our physics the forces are known and so QM=QFT in those domains. We don't have gravity encapsulated in QM and it was found that as the energies was increased in colliders that forces seem to merge. Our highest point we have gone back to electroweak theory (https://en.wikipedia.org/wiki/Electroweak_interaction).

You may want to review the known and expected field merges


So at this stage we are still in search of a Grand Unified Theory and higher up a theory of everything.

The question of whether QM requires and needs fields to operate is unanswered. All we can say is that it works in fields and even as those fields merge at higher energies. The question is hard to settle without the full theory of everything because the mathematics of QM works without the fields.

There are no known discrepancies between QM or QFT with any experiment ever done.

Last edited by Orac; 11/22/15 02:22 PM.

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Orac, this is truly off topic for what you are talking about, but you said that we are still in search of a Grand Unified Theory. You might get a laugh out of this. In the latest Scientific American there is an ad for a book titled "The Mechanical Theory of Everything", by Joseph M. Brown. The book explains:
Where energy comes from
How a Photon Dissipates in ten billion years
What Electrons and Protons are made of
The solution to Einstein's Unified Field Theory
How Language is made
and Why we age.

So you see all of the questions about the GUT and a whole lot more are already answered in this book for only $40 US. I'm not sure how the author got from Einstein to language, but it must be true, after all it is in a book.

And isn't that one of the most ridiculous things you ever heard of?

Bill Gill


C is not the speed of light in a vacuum.
C is the universal speed limit.
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Okay that is about the craziest book abstract I have ever read. I was hoping someone had done a review but I am guessing no-one was silly enough to part with $40.


I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.
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Originally Posted By: Orac
Non relativistic QM is like classical physics it can give wrong answers when given a problem it can't answer


So, do we have to draw a dividing line within QM, such that non-relativistic QM is on one side, and relativistic QM and QFT are on the other?


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Originally Posted By: Bill S.
So, do we have to draw a dividing line within QM, such that non-relativistic QM is on one side, and relativistic QM and QFT are on the other?

Are you deliberately being obtuse here?

Non-relativistic anything (substitute any word you like physics, QM, momentum, energy) is a simplification of whatever you are doing and is valid SO LONG AS YOU KNOW THE SPEEDS ARE LOW RELATIVE TO THE SPEED OF LIGHT.

In mathematics they call it approximation. So do you put approximation mathematics in a special section of mathematics that isn't really mathematics?

You layman sometimes approximate PI to 22/7 so do you put that in a special category of PI?

Doctors sometimes simplify disease treatments and go for broad spectrum antibiotics, is that a special category of medical treatment?

I think most intelligent people realize simplifications are used in just about every field that exists.

You come from a Geology background don't you so how do you treat theory simplifications in your field?

Last edited by Orac; 11/23/15 08:30 AM.

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Originally Posted By: Orac
Are you deliberately being obtuse here?


No, just trying to test my impressions. Your reaction suggests I was right to do that. smile

Quote:
You come from a Geology background don't you so how do you treat theory simplifications in your field?


No, my background was in mental health/criminal justice. Geology was a hobby for quite a long time, and I still dabble occasionally.
I suppose I was a bit of a nit-picker there as well. When the Open University said one of my answers was wrong, I argued until eventually they admitted I was right. They did say they they were "not looking for that depth of answer"; which I thought was a bit pathetic for a 2nd level university course.


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Originally Posted By: Bill S.
No, my background was in mental health/criminal justice.

Okay working that framework you would have some "rule's of thumb" or "expected results" which are simplifications based on a more detailed working of those systems and laws.

I am sure every now and again you will get a situation that your simplification doesn't work and you get a result outside the normal simplified range.

Does the fact your simplification doesn't work mean the original system was wrong?

I guess in your case the outcome might be unjust and you could use that as an argument to try and fix the detailed system.

In our case we don't have "unjust" and you can't just go an patch the detailed system, just so your simplification fantasy works. If the simplification doesn't work, but the full system does then the problem is with your simplification ... fix it smile


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Originally Posted By: Orac
Does the fact your simplification doesn't work mean the original system was wrong?


Of course not. I was just trying to be clear in my own mind about the distinction between non-relativistic and relativistic QM.

If you recall, my original question asked if QM required a universal time. Would it be right to say that non-relativistic QM does, but relativistic QM doesn't?

On the other hand, could it be that non-relativistic QM, if misapplied, gives answers that erroneously indicate a need for universal time?


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Yes non-relativistic QM uses Galilean relativity and it embodies absolute space and universal time as it is entirely like classical physics.

You can make it match to some extended non classical physics of atoms and particles by doing a series of fudge adjustments to the mathematics but there is no obvious reason why the fudges are needed. Without the fudge values the answers are as badly wrong as classical physics predicts.

In Relativistic QM the reason for the fudges and the values becomes obvious as being adjustments demanded by Special Relativity with it's relative space and non universal time. It also makes a number of predictions to do with spins that have no reason for being such in non-relativistic QM. It predicts things like anti-matter because it makes clear that negative energy must be just as valid as positive energy as you have no preferred reference frame. Again you can patch non-relativistic QM to embody these changes but in the meaningless way and concept that simplifications entail. I kept trying to make you look at negative energy which is a real problem in classical physics and it's preferred reference frame (Energy can only be positive).

Relativistic QM can answer almost every problem correctly except one that is close to your heart. It can not correctly describe matter creation and annihilation. You are probably going to ask why? The answer is simple it requires two particles to create or destroy and a reference frame connecting them as we are dealing with waves

https://en.wikipedia.org/wiki/Matter_creation
https://en.wikipedia.org/wiki/Annihilation

In the 1930's and 1940's it was thought that matter could neither be created nor destroyed, the phrase is often repeated in error even today. Dirac can be said to have made the first steps to solving this in 1933 but the point is arguable.

The only known theory and reference frame that can solve that problem is a field in QFT.

I am taking a hatchet to history here because there are some sub stories between this stuff but I think that is the level you want.

Last edited by Orac; 11/24/15 06:12 PM.

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Originally Posted By: Orac
In the 1930's and 1940's it was thought that matter could neither be created nor destroyed, the phrase is often repeated in error even today. Dirac can be said to have made the first steps to solving this in 1933 but the point is arguable.


When I first met this, in the 50s, it was expressed as: “Matter and energy cannot be created or destroyed, but they can be exchanged.”

Following your links, and reading Matt Strassler’s article, I have the impression that this still applies. Is that right?


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Again a highly loaded question to answer because it depends on what "you mean". I need to be clear what you are asking.

Please read:
http://profmattstrassler.com/articles-an...alse-dichotomy/

Ok so lets give you my version of a formal science answer:

Energy is just some currency that an observer creates relative to them. It is the same as if you live in the USA you use dollars, if you live in Europe you use Euros. All observers ultimately agree on the conservation of their own energy currency, so there exists a conversion calculation between any two observers energy currency but it may not be a trivial calculation.

To ask me whether you can create or destroy energy is an error to me, because you are assigning "existence" to energy. In it's broadest form energy equals information which is the approach QM takes. The problem is information exists only when there is an observer and now we have a problem to discuss.

For me energy doesn't exist to be created or destroyed, it is actually the observer that is created and destroyed smile

Can you create or destroy matter. Well yes you can we do it all the time and it occurs naturally in radioactive decay processes. However that probably isn't what you meant, what you were really asking is can matter be built from nothing or perhaps pure energy or go back to those things, depending on what lead you to the question in classical physics.

From our discussion above on energy it could not build anything as it doesn't exist except as an accounting concept to some observer. So you certainly can't build matter from energy. So can you build it from nothing or make it go to nothing, well that is going to depend how you define nothing.

From my previous post the only theory that can describe matter creation and annihilation is QFT and a field is neither energy nor matter, it is something else and Matt nicely summed it up

Originally Posted By: Matt
What do “fields and particles” have to do with “matter and energy”? Not much. Some fields and particles are what you would call “matter”, but which ones are matter, and which ones aren’t, depends on which definition of “matter” you are using. Meanwhile, all fields and particles can have energy; but none of them are energy.

When you had gone thru QFT, I tried to get look at the concept of the field and what the hell it is.

Matt stated it this way
Quote:
The stuff of the universe is all made from fields (the basic ingredients of the universe) and their particles. At least this is the post-1973 viewpoint.

So if the universe is built of fields what I really need from you is how you define what I call fields. Given that I can possibly give you an answer we will both see as logical.

I have a religious friend who whenever anyone says they created something from nothing says, "GOD asks that you bring you own fields please, and stop using his".

Sorry I can't give a shorter answer but I need to be very clear what you are asking.

Last edited by Orac; 11/25/15 02:36 AM.

I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.

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