# Who was there to observe the early universe?

#### eehiram

I have been reading Jim Al-Khalili's book, Quantum: A Guide for the Perplexed, and in chapter 5, on page 122, the author suggested that perhaps the moon slips into quantum uncertainty when no one is observing it.

If this is neccessary, then what happened to the early universe? Surely there was no observation going on? There is the quantum sized universe immediately after the big bang and the billions of years that followed before there were any living things to observe anything at all.

BTW, that book is an indication of my level of understanding of QM, so please don't baffle me with complex differential equations. I just read layman's terms books along the lines of Stephen Hawking, Brian Greene, and Richard P. Feynman.

o| Hiram

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#### chroot

Staff Emeritus
Gold Member
Quantum mechanics does not involve, nor need to involve, any concept of a sentient or conscious "observer" to function. Anyone who tells you that human observation is somehow relevant to quantum mechanics is lying to you.

- Warren

#### eehiram

In that case, how do the rules of QM bear upon the early universe -- such as when the universe was small enough to pertain to QM rules?

#### eehiram

Or could you at least elaborate a little on what the correct QM interpretation would be, then?

#### masudr

According to quantum mechanics, we can associate every physical system with a mathematical object called the state vector as a function of time, often denoted as $| \psi(t) \rangle$. This object is perfectly well defined, and satisfies a certain equation (the Schrödinger equation).

According to quantum mechanics, there is an operator (called the time evolution operator) that will take the state vector at one particular point in time to another point in time. In symbols:

$$| \psi(t) \rangle = U(t, t_0) | \psi(t_0) \rangle.$$

Here, $U(t, t_0)$ is the time evolution operator, and in this case it is taking the state vector from time $t_0$ to time $t.$ Some properties of the time evolution operator are given in the Wikipedia article on the Schrödinger picture, edited at 09:16, 7 Jan 2007.

As you can see, this has nothing whatsoever to do with observers of any kind. After all, observers are only other physical systems, who are also described by state vectors: the observer-observed separation is artificial but is often done to ease the burden of computation.

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#### hellfire

Or could you at least elaborate a little on what the correct QM interpretation would be, then?
I think this is a very interesting and difficult question. The Copenhagen interpretation, in which it is needed to have an external observer to the system that collapses the wavefunction, is clearly not acceptable in quantum cosmology. Other interpretations like the Everett interpretation, or the Consistent Histories together with quantum decoherence, are more popular in quantum cosmology. Eventually one has to find a mechanism to explain how and why we observe classical phenomena.

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#### lightarrow

I have been reading Jim Al-Khalili's book, Quantum: A Guide for the Perplexed, and in chapter 5, on page 122, the author suggested that perhaps the moon slips into quantum uncertainty when no one is observing it.

If this is neccessary, then what happened to the early universe? Surely there was no observation going on? There is the quantum sized universe immediately after the big bang and the billions of years that followed before there were any living things to observe anything at all.
How do you know it?
1. If you mean something related to human's being activity, surely not, but who can prove no being from other universes cannot "observe" our?
2. What does Actually mean "observation"? It's not a trivial concept at all.

#### eehiram

I was ready to give up on the observation questions and simpy ask how QM bears upon the early universe, but since you are asking, then I was referring to the Copenhagen interpretation defnition of a classical observer that collapses the wavefunction and removes (or lessens?) the Heisenberg's Uncertainty value of momentum.

Therefore I would discount other beings and simply stick to biology for classical observers.

I think the original question applies as well to areas of the universe not well observed by humans on account of distances and dimness. However, I assume you are going to tell me that works somewhat differently.

#### eehiram

exact quote from Quantum: A Guide for the Perplexed

"Does the Moon exist when we are not looking? Since it too is ultimately composed of atoms it should behave like a very large quantum object. Maybe when you turn your back it smears out into a hazy superposition of being in all locations that its wavefunction has spread to since you last looked at it."

#### ZapperZ

Staff Emeritus
2018 Award
"Does the Moon exist when we are not looking? Since it too is ultimately composed of atoms it should behave like a very large quantum object. Maybe when you turn your back it smears out into a hazy superposition of being in all locations that its wavefunction has spread to since you last looked at it."
There is ONE very important issue that you have completely ignored: there are two dichotomy in our world, which are the classical world, and the quantum world.

What you are trying to do is what most people try to do when they deal with metaphysics - extending what we know that works within a particular domain into something in which the rules are now different. This applies both ways - when someone extend classical concepts into quantum world, or when someone applies quantum concepts into classical world. Inevitably, both often lead to absurdity.

We know the rules at the classical scale, and for all intent, these rules work! That is a very powerful argument against many of these absurd metaphysical extension. The same can be said when people are insisting that our classical concepts should be applied equally well at the quantum scale. They don't!

What happens in between, often call the mesoscopic scale, is something that is still an active fundamental research area. Until we know better, all we have the ability to know are the two extreme cases. There is nothing that tells us that going from one to the other is a smooth transition. It could easily be some form of a phase transition where our knowledge simply undergoes an abrupt change. So your effort at extending the quantum concepts into the classical concept may be invalid.

Zz.

#### eehiram

Moon is from the classical world, then?

Am I to infer that the Moon is from the classical world and the quantum rules do not apply to it? You did not actually state this in your post, but I assume that's what you meant.

If so, then I think the question is relevant in terms of quantum cosmology, which has been replied to.

I'm a little unclear about how aggregation of nuclear scale uncertainty works, as I know that Heisenberg's Uncertainty Equation relates uncertainty in momentum to Planck's constant; hence, the moon's momentum would be large and hence uncertainty would be small.

However, the moon is made up of individual atoms whose uncertainty would be far greater, right?

o| Hiram

#### eehiram

Hellfire, I just finished reading the chapter on QM interpretations this morning, so I understand now a little bit about the Everett (multiple parallel universes) and consistent histories (no need for observers to collapse the wavefunction) interpretations.

I guess my question behind my question is how could the universe emerge from quantum scales and evolve for billions of years in superposition? Allowing for that kind of a history, even if it is mistaken, at what point would it's wavefunction have collapsed?

The reason I ask all these questions about QM and the Big Bang is that in the simplistic explanations I have read on the Big Bang and early universe, the Big Bang is not described on QM lines but more simply, like a classical event. In fact, according to my most up-to-date description in Astrononmy magazine, QM rules emerged a certain amount after the Big Bang itself, so perhaps...just perhaps...QM does not apply to the universe before that. Instead, there were the so-called "exotic laws of physics".

o| Hiram

#### ZapperZ

Staff Emeritus
2018 Award
This is where I lose your admiration. After reading that last response from the OP, I think I'm going to give up. I don't think I have the patience to dig THAT deep.

Zz.

#### hellfire

I guess my question behind my question is how could the universe emerge from quantum scales and evolve for billions of years in superposition? Allowing for that kind of a history, even if it is mistaken, at what point would it's wavefunction have collapsed?
Probably you have already noticed that there is no firmly established answer to such a question. Starting from the assumption that the universe begun in an initial state behaving as a quantum system, the requirement is to describe the emergence of classicallity, a mixed state, 14 billion years afterwards. There are various approaches to explain this, among them relying on the Everett interpretation, quantum decoherence, etc. The whole issue is very complex and the proposals are very speculative.

The reason I ask all these questions about QM and the Big Bang is that in the simplistic explanations I have read on the Big Bang and early universe, the Big Bang is not described on QM lines but more simply, like a classical event. In fact, according to my most up-to-date description in Astrononmy magazine, QM rules emerged a certain amount after the Big Bang itself, so perhaps...just perhaps...QM does not apply to the universe before that. Instead, there were the so-called "exotic laws of physics".
There is currently no experimentally validated theory of quantum gravity that can provide a model for quantum cosmology. However, in both main candidates, string theory and loop quantum gravity, the principles of quantum mechanics remain always valid.

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#### heusdens

About this QM interpretation involving consciouss observers and collapse of the wave function, here's an example that would conflict this interpretation.

Think of the very far remote galaxies. They too are in a superposition of states, as QM envisions it. But then, after billions of years, we finaly observe them, and make observations, identifying the state of that galaxy.

Now if the act of observing this galaxy would make the wave function collapse, this information then somehow reaches us instantaniously?

Or we would need to interpret it as follows, that only the light emitted from that galaxy in a superposition of states, would have a collapsing wave function.
But then this collapse of the wave function travels back to the galaxy?

Suppose another observer, also very far remote from the galaxy, and also very far remote from us, which is at the same distance of the observed galaxy as we and makes the observation at the 'same time' (this is however in the context of SR some difficult to state), then also that observation causes the wave function to collapse, independently of our observation.
So, that outcome might be different, which means the galaxy has then two different states?

Btw. I don't think it's meaningfull to talk about probabilities for larger objects, when significantly larger then atoms.

#### eehiram

Again, thanks for the replies

hellfire, it sounds, then, like the classical physics description of the Big Bang and the emerging universe is the only established one, then, even with the universe smaller than an atom. Well...I guess we'll all have to wait for string theory or loop quantum gravity to finally be worked out, then.

When you wrote the principles of QM remain always valid, it sounds like you meant they applied to the Big Bang itself. I thought the laws of science started to take shape some time after the Big Bang, like the four fundamental forces of physics.

heusdens, yes that is what I was thinking about also. I don't know how fast the collapse of the wavefunction can travel, so I can't answer for your objections.

And although I agree that galaxies are much larger than an atom, there is no one to observe distant galaxies as far as my understanding of biology is concerned. So...perhaps they ARE in a state of superposition, then, and remain so from the beginning until the end of the universe.

#### setAI

the issue of how to deal with the implications of QM and the 'the past' are coming to the fore these days- for example this is what Hawking has been working on lately: http://arxiv.org/abs/hep-th/0602091- [Broken]

the idea that what we call the past is not a single history but rather the sum-over histories of every possible type of universe- this understanding that Time is not singular history but rather probabilistically emerges from a superposition of possible histories will be crucial going forward

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