# Consciousness and QM

1. Jul 18, 2015

### Pete Hammand

Just curious, but has this theory been completely disproven? Is it possible to even debate that this is the case? It seems to me that some of the founders of QM such as Heisenberg, Pauli, and even Max Planck toyed with this idea and considered it a possibility. Why is it not any more? I don't see any issue with it being plugged into the equation. If it helps solve the puzzle then why not?

2. Jul 18, 2015

### stevendaryl

Staff Emeritus
Well, there is absolutely no evidence for believing that a conscious observer has any different role in QM than a nonconscious recording device such as a camera. So I don't think there is any special role for consciousness.

I think decoherence has mostly replaced the role that conscious observation once played in QM.

3. Jul 18, 2015

### Pete Hammand

I see. But I had this weird thought, that maybe the decoherence is simply the particle 'knowing' that a conscious observer is measuring it. Not the result of any phenomenon of interacting with the measuring device. It is also hard to eliminate the observer by the very fact that we look at the data...

4. Jul 18, 2015

### atyy

I think there is still disagreement on this issue. Here is Ed Witten saying it seems to be a problem (especially 3:00 - 3:10).

5. Jul 19, 2015

### bhobba

Of course it hasn't been disproven, nor can it be. Its like solipsism - inherently not provable. Its just a ridiculously weird view of the world that only those attracted to such would embrace.

If you want to know why it gained some adherents read Mathematical Foundations Of Quantum Mechanics by Von Neumann. But the key point is with our modern understanding of decoherence his argument no longer holds.

Thanks
Bill

6. Jul 19, 2015

### maline

I don't agree. The measurement problem has several aspects, and decoherence helps with some of them, such as how the measurement basis is selected. But the more fundamental ontological problem, if I understand correctly, goes something like this:
Is the wavefunction/ quantum state an entity that exists in space & time, or is it strictly a tool for calculating (probabilistic) results of measurements?
If it is not real, then what does exist between measurements?
But if it is real, then what happens to it after a measurement?
If it "collapses", & this is seen as an objective occurrence, then what could cause such a thing to happen?
Wigner & von Neumann suggested that since all of inanimate matter can be included in the quantum state, whose evolution does not allow for collapse, it must be that collapse as an objective occurrence is caused by interaction with something nonphysical- i.e. consciousness.
Nowadays this is not taken seriously, for one thing because few (scientifically-minded) people still believe that consciousness is nonphysical. Also, can you really believe that the universe was in a superposition of all possibilities for billions of years, until a conscious animal evolved in one tiny branch, at which point the whole thing suddenly collapsed?
The "orthodox" approach to the problem is that the state is not assumed to be real, but that the question of what does exist between measurements is outside the realm of science because, by definition, it has no observable effects.
Those who are not satisfied with this pursue "interpretations" such as many-worlds or bohmian mechanics, or alternative models such as dynamic collapse.

7. Jul 19, 2015

### Fredrik

Staff Emeritus
QM says that interactions with the environment will quickly change a quantum superposition into something that's indistinguishable from a classical superposition ("it's one of the options; we just don't know which one"). You're suggesting that the real reason isn't that matter behaves quantum mechanically, but that it knows what we're doing. That is a weird thought indeed.

This is true, but it doesn't in any way suggest that consciousness causes collapse.

8. Jul 19, 2015

### Derek Potter

The Hard Problem remains hard in QM. However it is easily circumvented. In order to explain consciousness of outcomes one postulates that one's experience supervenes on the state of the brain. One should then follow up by asking why anyone would want to introduce metaphysics into physics.

9. Jul 19, 2015

### craigi

If you replace the concept of a particle 'knowing' that it is being observed with its state being relative to that of the observer then your line if inquiry will be more fruitful.

For the majorty of physicists consciouness is a concept from neuroscince and philosophy and they strongly object to it playing any fundamental role in quantum theory or cosmology so you will encounter much resistance here.

I suggest you read some Tegmark and Penrose, then for the philosophy
read Chalmers and try to follow the advances in neuroscience.

Last edited: Jul 19, 2015
10. Jul 19, 2015

### Pete Hammand

Thank you for that reply that really is interesting. To be honest, I think Von Neumann was on to something. The Von Neumann chain is 'cut' once it reaches it's final destination, which is the conscious observer who determines the final outcome-giving certainty. IMO certainty has no meaning without the observer. The particles alone don't bringing certainty.

11. Jul 19, 2015

### Derek Potter

Then they haven't thought about it.
Why not? The state space defines all those possibilities. Why should the state vector have to hug a basis state?

Last edited: Jul 19, 2015
12. Jul 19, 2015

### Pete Hammand

I also see your point too, it is odd to think, but maybe consciousness DID exist somehow, but it isn't within our understanding currently of how it did. Because our paradigm says brain creates consciousness, but if it is indeed the other way around, then consciousness must have existed all the way back to the Big. Bang.

13. Jul 19, 2015

### Derek Potter

Sure, if you assert that the final destination is consciousness then consciousness has a special role. And if you assert that the final destination is The End of Time then we are in a Many Worlds superposition until then.

14. Jul 19, 2015

### Derek Potter

Why are you still saying this? You idea is based on a myth which several people here have shown you is outmoded and incorrect. If you don't understand then you should ask, or even challenge them! Please don't keep reiterating your own opinion when it has been refuted.

15. Jul 19, 2015

### Pete Hammand

I think it scares physicists to think of the implications of consciousness being fundamental, because this worldview implies that there is no 'real world' out there, it's simply a construct of consciousness. It's much more neat and tidy to think of it as a great machine rather than a great thought. But as you said there are many interpretations, and most scientists seem to think that this is not the case.

16. Jul 19, 2015

### maline

By "nonphysical" I mean "not describable in terms of physical processes", or, in your own words, not supervening on the physical state of the brain (& body).

Just to make clear: the unbelievability lies in the "until... suddenly". The many worlds interpretation, which Derek is very excited about, has an uncollapsed state that just continues for all time. That has its own difficulties, but not this particular absurdity.

Last edited: Jul 19, 2015
17. Jul 19, 2015

### Pete Hammand

I'm not really saying this is a case in a scientific view. That was more of a philosophical statement that you need to think about. It's a silly argument , but a simple one. The only way we can be 'sure' anything exists is through conscious observation, this applies to science, or any area of life for that matter.

18. Jul 19, 2015

### Derek Potter

"We don't do philosophy here" Regrettably this forum has a Philosophy Police who will close a thread even if it is still very active and productive if anyone veers off into something even slightly smelling of philosophy. QM is grounded in certainty and reality through the Postulate of Observations. Observation is imported directly, intact and unexplained into QM from everyday life. It would therefore be ridiculous and quite wrong to expect QM to do anything about "certainty" and "reality" that goes beyond what everyday experience provides.

19. Jul 19, 2015

### stevendaryl

Staff Emeritus
I think that it should be possible to formulate the empirical content of QM in a way that doesn't mention observations or observers or consciousness. Something along the lines of this:

Let $\mathcal{S}$ be the set of all macroscopically distinguishable states of the universe. One way to specify this might be to divide up the universe into tiny little cells, and for each cell, describe the contents of the cell in coarse-grained terms: the average number of particles of various types, their average kinetic energies, the total momentum and angular momentum, the average values of electrical and magnetic fields within the cell, etc.

Then we come up with the following mappings:
1. If $s$ is the macrostate at some time, then assume we have some recipe for computing $\rho_s$, which is a corresponding quantum-mechanical density matrix for the universe (or just for the region of interest).
2. As sort-of an inverse, if $\rho$ is a density matrix, then let $P_\rho(s)$ be a corresponding probability distribution on macroscopic states.
3. If $\rho$ is any density matrix, then let $\rho(t)$ be the result of evolving $\rho$ using the Schrodinger equation for a time $t$
Then in terms of these functions, we can formulate the empirical content of quantum mechanics in a way that doesn't mention observers or observations or measurements or consciousness by saying:
If the universe starts off in macroscopic state $s$, then after time $t$, it will be in state $s'$ with probability $P_{\rho_s(t)}(s')$​

20. Jul 19, 2015

### Derek Potter

I am prepared to defend MW from misrepresentation but I do not impose it on an argument, indeed in this case I am explicitly talking about collapse theories. I agree that the "until suddenly" aspect is a different one from the "great big superposition" one but the silliness of it is in assuming a causal role of consciousness at all, not the suddenness. Thank you for reminding me that MWI has its own difficulties, by the way. I must be getting old but I can't seem to remember what they are.