Quantum Biology: Life on the Edge - Where is the Electron?

[rasp]

Reading Life on the Edge by McFadden and Al-Khalili. I know quantum biology is a controversial subject but my question is very traditional. The authors state" the quantum wave function is spread out over all space" " only through the act of looking can we force the electron to be a localized particle" my question is if the electron is spread over all space what does it mean to assign probability to its location? Secondly if we look for the electron in a localized space and DON'T find it have we still collapsed the wave function? Thanks rasp

 

[ZapperZ]

Reading Life on the Edge by McFadden and Al-Khalili. I know quantum biology is a controversial subject but my question is very traditional. The authors state" the quantum wave function is spread out over all space" " only through the act of looking can we force the electron to be a localized particle" my question is if the electron is spread over all space what does it mean to assign probability to its location? Secondly if we look for the electron in a localized space and DON'T find it have we still collapsed the wave function? Thanks rasp

Just so you know, the title you have given here is inaccurate, because your question has more to do with the nature of the QM wavefunction, the concept of quantum superposition, and the meaning of measurement. These are not "quantum biology" issues.

Now that I've told you a bit on what your question actually corresponds to, if you browse through the thread in this forum, you'll see these topics in their various forms already being discussed. Look for anything that has "Schrodinger Cat", "Superposition", "Collapse", etc..

BTW, assigning a probability to its location means that it is the probability that you'll find the electron at that particular location. Or, if you have a gazillion identical atoms, then a fraction of this population corresponding to that probability will have the electron in that very location at a given instant.

Zz.

 

[Khashishi]

A measurement of no will still collapse the wavefunction.

 

[rasp]

Thanks for the redirect. But again on the probability question, it seems that if the electron is spread everywhere at once then it could be found everywhere.

 

[Feeble Wonk]

Thanks for the redirect. But again on the probability question, it seems that if the electron is spread everywhere at once then it could be found everywhere.

Speaking as a fellow non-physicist, I think I might be able to address your confusion on the primary point.
The electron ISN'T "everywhere at once". The electron MIGHT BE anywhere at any given time... hence the "probability" designation of the wave function. But even that is an over simplification.

Your take away understanding from this should be that the electron, being a fundamental particle, does not behave "classically"... as most of us non-physicists think things should... but instead, are subject to quantum effects that make things like being in a precise location a very fuzzy thing. Try not to think of the electron, or any fundamental particle, as being an infinitesimally small BB that moves around in a continuous fashion. Most physicists don't believe that's an accurate depiction.

There are interpretations of quantum theory that hypothesize a continuous "particle" status to the fundamental particles, but that gets into a more complicated discussion of theory than you probably need to worry about for your purposes.

 

[Derek Potter]

if you browse through the thread in this forum, you'll see these topics in their various forms already being discussed. Look for anything that has "Schrodinger Cat", "Superposition", "Collapse", etc..

And when you see one... Run!

 

[jerromyjon]

Thanks for the redirect. But again on the probability question, it seems that if the electron is spread everywhere at once then it could be found everywhere.

All of it will be found somewhere.

 

[ZapperZ]

Thanks for the redirect. But again on the probability question, it seems that if the electron is spread everywhere at once then it could be found everywhere.

I don't quite understand this, and it seems that you have more of an issue in understanding basic statistics rather than quantum probability.

Sure, it does mean that an electron can be found in the region where the probability isn't zero. But it doesn't mean that you are guaranteed to find it where you look every single time on identical atoms! That is why I said earlier that you will have a probability of finding an electron at a particular location at a particular time, or if you have many, many identical atoms, then when you look at all of them, then a fraction corresponding to that probability will have an electron in that location.

Example: The probability that an electron is at location r1 at a particular time is 25%, or 1/4. That means that you have a 1 in 4 chances of finding an electron at that location. But it also means that if you have 100 of this identical atoms, if you look for the electron in all of these atoms, you will find that 25 atoms will have the electron in that same location. The rest won't!

Zz.

 

[rasp]

Thanks feeble wonk. Your simple explanation that the electron is Not everywhere at once but only May be anywhere at any given time resolves my confusion over the probability factor.

 

[ZapperZ]

Thanks feeble wonk. Your simple explanation that the electron is Not everywhere at once but only May be anywhere at any given time resolves my confusion over the probability factor.

Unfortunately, if you stick to that, you will have a "fun" time trying to reconcile the double-slit experiment.

Zz.

 

[Feeble Wonk]

[emoji39] I said it was an over simplification. I was trying to avoid frying the OP's mind more than necessary.

 

[atyy]

Thanks feeble wonk. Your simple explanation that the electron is Not everywhere at once but only May be anywhere at any given time resolves my confusion over the probability factor.

That's fine - with one important qualification - the particle may be anywhere at a given time, if one is making a measurement of the particle's position at that given time. Also, the particle may have any momentum at a given time, if one is making a measurement of the particle's momentum at that given time.

Now, one may be tempted to say that this means the particle has a definite position at a given time, and we don't know it.

Or that the particle has a definite momentum at a given time, and we don't know it.

However, what is forbidden is to say that the particle has a definite position and momentum at a given time, and we just don't know it.

For this reason, we cannot think of the outcomes of all measurements as measuring simultaneously pre-existing properties of the particle, and we must specify which measurement is being performed. In fact, we also cannot simultaneously and accurately measure an arbitrary particle's position and momentum.

A loophole is that the term "momentum" is very technically defined, and is it possible for a particle to have a definite position (but not momentum) at all times? Can a particle have a trajectory? In non-relativistic physics, that seems to be a possibility called Bohmian Mechanics. Bohmian mechanics can also model some relativistic quantum phenomena, but it is not yet known if Bohmian Mechanics can be extended to all relativistic quantum phenomena.

 

[Feeble Wonk]

That's fine - with one important qualification - the particle may be anywhere at a given time, if one is making a measurement of the particle's position at that given time. Also, the particle may have any momentum at a given time, if one is making a measurement of the particle's momentum at that given time.

Now, one may be tempted to say that this means the particle has a definite position at a given time, and we don't know it.

Or that the particle has a definite momentum at a given time, and we don't know it.

However, what is forbidden is to say that the particle has a definite position and momentum at a given time, and we just don't know it.

For this reason, we cannot think of the outcomes of all measurements as measuring simultaneously pre-existing properties of the particle, and we must specify which measurement is being performed. In fact, we also cannot simultaneously and accurately measure an arbitrary particle's position and momentum.

I think I hear the sizzle of innocent OP gray matter. [emoji85] The rabbit hole can be a little scary at times rasp, but it's a fun ride. Enjoy.

A loophole is that the term "momentum" is very technically defined, and is it possible for a particle to have a definite position (but not momentum) at all times? Can a particle have a trajectory? In non-relativistic physics, that seems to be a possibility called Bohmian Mechanics. Bohmian mechanics can also model some relativistic quantum phenomena, but it is not yet known if Bohmian Mechanics can be extended to all relativistic quantum phenomena.

And yes, this is the QT interpretation that I was referring to.

 

[Feeble Wonk]

But of course, it IS a much more complete and accurate explanation.

 

[jerromyjon]

But of course, it IS a much more complete and accurate explanation.

I think you need get firmly planted on the "plateau" of quantum physics, and how it differs from classical physics, before you can try to climb higher up the ladder into different interpretations and attempt to seek deeper understanding.

 

[Feeble Wonk]

I think you need get firmly planted on the "plateau" of quantum physics, and how it differs from classical physics, before you can try to climb higher up the ladder into different interpretations and attempt to seek deeper understanding.

That's what I suggesting as well.