# What is the definition of future according to quantum mechanics?

#### amrani

Hello,
I really need your help dear friends, I had this question in an interview :
What is the definition of future according to quantum mechanics? And how can we create and improve our future??
they asked me to write a three-page texte. I must respond them tomorrow.

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#### e.bar.goum

What kind of job? And I'm sure they really wanted your opinion, not that of all of us. :)

Time in quantum mechanics is a parameter of the wave-function. (The parameter, in the case of straight-up QM, one of the parameters, along with space in the case of QFT). Wave functions evolve over time as given by the Schrodinger equation

$i \hbar \frac{\partial}{\partial t} \Psi = \hat{H} \Psi$

#### amrani

What kind of job? And I'm sure they really wanted your opinion, not that of all of us. :)

Time in quantum mechanics is a parameter of the wave-function. (The parameter, in the case of straight-up QM, one of the parameters, along with space in the case of QFT). Wave functions evolve over time as given by the Schrodinger equation

$i \hbar \frac{\partial}{\partial t} \Psi = \hat{H} \Psi$
Its a job at SAMSUNG? if i had that opinion so why am i asking for your help

#### e.bar.goum

What a strange job interview question!

I would muse on what I said above. What does it mean that time is a parameter of the Schrodinger equation? What does that imply for time evolution, and the future?

Now, this is where it depends on exactly the kind of job you're going for: You can either get technical, or you can get philosophical. You could also get metaphysical, but I personally would shy away from that.

Also, consider that perhaps the second part of the question is more important than the first. But isn't too much to do with QM, unless you go into fake woo science (I hope the person asking the question knows quantum mechanics, I really do).

Good luck, and welcome to PF!

#### amrani

What a strange job interview question!

I would muse on what I said above. What does it mean that time is a parameter of the Schrodinger equation? What does that imply for time evolution, and the future?

Now, this is where it depends on exactly the kind of job you're going for: You can either get technical, or you can get philosophical. You could also get metaphysical, but I personally would shy away from that.

Also, consider that perhaps the second part of the question is more important than the first. But isn't too much to do with QM, unless you go into fake woo science (I hope the person asking the question knows quantum mechanics, I really do).

Good luck, and welcome to PF!
that's what I thought too, and I also think they do not want to hire me so they gave me this.

because I studied the modulus of the structure of matter and atomic physics nuclear in my first year of university and we saw classical mechanics, the Bohr model, wave particle duality and etc ...
so when they asked me that question I didn't found a logical explanation.

Thank you very much.

#### moriheru

Hello,
I really need your help dear friends, I had this question in an interview :
What is the definition of future according to quantum mechanics? And how can we create and improve our future??
they asked me to write a three-page texte. I must respond them tomorrow.

The hole point is that the future of a system is can not deterministic. Schrodingersequation describes the n+1 state of a system with a exponential factor which is derived from a differential which is well known and is fundamental. But I am guessing this has less to do with the mathematics of QM.

#### amrani

The hole point is that the future of a system is can not deterministic. Schrodingersequation describes the n+1 state of a system with a exponential factor which is derived from a differential which is well known and is fundamental. But I am guessing this has less to do with the mathematics of QM.
Thank you. But how must i reply and think about the answer if we suppose it has something to do with physics and QM.

#### moriheru

Three pages is a lot! Are you talking about the future of our lifes that is to come ,because of quanutm mechanics or the general concept of the future as one would name it in QM?

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#### atyy

In some interpretations, quantum mechanics does require at least locally, an arrow of time. For example, in Copenhagen a measurement is an irreversible macroscopic mark. In some forms of Many-Worlds, the branching structure seems to provide or depend on an arrow of time. Mathematically, this is because quantum mechanics has two sorts of time evolution. There is unitary, time reversible evolution by the Schroedinger equation, but there is also non-unitary time evolution given by wave function collapse. In the Bohmian interpretation there would appear to be some form of irreversibility at the coarse grained level needed to establish "quantum equilibrium" (a technical term in the Bohmian interpretation).

This issue is discussed in:
https://www.amazon.com/dp/3540610499/?tag=pfamazon01-20 (Chapter VII.3: The Evolutionary Picture)
https://www.amazon.com/dp/0199546967/?tag=pfamazon01-20 (Chapter 9: The Directions of Branching and the Direction of Time)
http://arxiv.org/abs/1001.2758 (see the section on quantum non-equilibrium)

There is also work on how coarse grained observables and unitary time evolution can give rise to an arrow of time, ie. give rise to the second law of thermodynamics. This idea goes all the way back to von Neumann:
http://arxiv.org/abs/1003.5424

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#### dipole

Sounds to me like you've serious misunderstood the question... and supposing you didn't, if you do get hired are you going to post on these forums every time you're given a task and not sure what to do? Companies aren't hiring you for your ability to ask questions on physics forums...

#### mfb

Mentor
The hole point is that the future of a system is can not deterministic.
The equations of quantum mechanics are deterministic. Some interpretations of quantum mechanics are non-deterministic.

#### amrani

Sounds to me like you've serious misunderstood the question... and supposing you didn't, if you do get hired are you going to post on these forums every time you're given a task and not sure what to do? Companies aren't hiring you for your ability to ask questions on physics forums...
thank's for your opinion and i respect. but if you read my conversation and posts I wrote you'll understand why I want to have the answer:

"that's what I thought too, and I also think they do not want to hire me so they gave me this.

it means: I'm looking for the answer for me to cultivate, to expand my knowledge.

don't worry about the interview , it's too late for me timeout
thank's again ;)

#### Demystifier

2018 Award
What a strange job interview question!
I think it's a trick question. Perhaps they are testing how do you react to stress caused by a confrontation with an unsolvable (or irrelevant) problem. ;)

Now, this is where it depends on exactly the kind of job you're going for: You can either get technical, or you can get philosophical. You could also get metaphysical, but I personally would shy away from that.
In this case, what would be the difference between "philosophical" and "metaphysical"?

#### e.bar.goum

I think it's a trick question. Perhaps they are testing how do you react to stress caused by a confrontation with an unsolvable (or irrelevant) problem. ;)

In this case, what would be the difference between "philosophical" and "metaphysical"?
I definitely agree that it was likely a trick question.

I was trying to distinguish between philosophical as in questions that may be reasonably asked in studies of Philosophy of Science, and metaphysical, as in "woo, quantum mechanics is so spooky, anything can happen, woah", which are asked by people who have no idea what quantum mechanics actually is. That last sentence was very tongue-in-cheek. :P

#### Demystifier

2018 Award
I definitely agree that it was likely a trick question.
I've heard of a case in which a pharmacy company (Pliva, for those who heard about it) had the following interview question: Write 100 sentences which start with "I".

I guess a typical answer starts like this:
1. I am hard-working.
2. I am honest.
3. I would really like to work in your company.
.
.
.
But after you get exhausted you start to make answers which may show how you react to frustration:
40. I think this is a stupid question.
.
.
.
or how creative and efficient you are:
60. I will finish the task in the simplest possible way.
61. I am.
62. I am.
63. I am.
64. I am.
.
.
.
99. I am.
100. I am.

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