Cosmology - The Quantum Multiverse in Scientific American of June 2017

This document contains comments about the article The Quantum Multiverse by Yasumori Nomura In Scientific American of June 2017.
A surprising connection between cosmology and quantum mechanics could unveil the secrets of space and time.

"Introduction"

The article starts which two exceptional claims.
Many cosmologists now accept the extraordinary idea that what seems to be the entire universe may actually be only a tiny part of a much larger structure called the multiverse.
The only thing that is true that of the present universe (based on certain assumptions about the expansion of the universe) we humans can only observe a tiny part. Most of what we observe lies in the past.
In this picture, multiple universes exist and the rules we once assumed were basic laws of nature take different forms in each; for example the types and properties of elementary particles may differ from one universe to another.
IMO the elementary particles (of the periodic table) throughout the whole Univese at present are every where the same.
If someone believes otherwise he or she should clearly explain how this can be 'demonstrated'.
Yet the multiverse notion, with its unlimited number of bubble universes ,does present a major theoretical problem: it seems to erase the ability of the theory to make predictions - central requirement of any theory.
When you can not make predictions, Yes there is a serious problem.
See also: Reflection 1 - A theory versus a law

Quantum Many Worlds

In the quantum - a nonintuitive place - cause and effect work differently than they do in the macro world and the outcome of any process is always probabilistic.
The main problem is that we humans can not make accurate observations to determine the state of the system at microscopic level. The same also happens at macroscopic level in some sense. This has 'nothing' to do with cause and effect. The problem is accuracy.
Whereas in our macroscopic experiment we can predict where a ball will land when it is thrown based on its starting point, speed and other factors,
These other factors are important which makes the prediction probabilistic.
if that ball were a quantum particle we could only ever say it has a certain chance of ending up here and an other chance of ending up there.
Not true. The two situations are in essence the same. They are both probablistic.
The only thing that is true, is that we humans now less at microscopic level, with the emphasis on we
page 25
In the quantum world we say that after the ball is thrown, but before we look for its landing spot, it is in a so-called superposition state of outcomes A and B - that is, it is neither at point A nor point B but located in a probabilistic haze of both points A and B (and many other locations as well)
What is the definition of the word located in this sentence?
Once we look, however, and find the ball in a certain place - say point A - then anyone else who examines the ball will also confirm that it sits at A.
When you observe and the ball is at place A then always before you look the ball is also somewhere. . This does not have to be at place A, but the ball is somewhere.
In other words, before any quantum system is measured, its outcome is uncertain, but afterward all subsequent measurements will find the same result as the first.
That is always true. The whole issue is that ball is never in a superposition state, i.e. being in two states simultaneous.
The reader is adviced to read the real article.
Does the state of change occur when a dog or even a fly observes the system?
Any observation in some sense has nothing to do with the true state of the system, except if the observation directly influences the state.
In 1957 Hugh Everet, developed the many worlds interpretation of quantum mechanics etc.
A concept like many worlds makes the issues involved overly complex. First of all you need a good definition of what a world (one of many) is.
Everett's key insight was etc so we must include the observer in a complete description of the measurement.
If the observer does not interfer which what is measured you do not have to take that into account. The measurement device has to be discussed.
etc we must also include in the fundamental description the person who comes along to inspect its landing spot, as well as everything else in the cosmos at that time.
No
Next page.
A human observer, being part of nature, cannot escape from this cycle - the observer keeps splitting into many observers living in many possible parallel worlds.
What is the physical significance of this concept?
An obvious but important implication of this picture is that everything in nature obeys the laws of quantum mechanics wheteher small or large.
If that is true than quantum mechanics has no scientific meaning or value.
In this understanding ,the infinitely large space associated with ternal inflation is a kind of "illusion" - the many bubble universes of inflation do not do not all exist in a single real space but represent the possible different branches on the probabilistic tree.
This sentence introduces doubt. Is there one universe or are there more? It seems the author is in doubt. Trees have branches and in my mind I can have different thoughts but none of these thoughts represent a physical reality.
If true, the many worlds interpretation of the multiverse would mean that the laws of quantum mechanics do not operate solely in the microscopic reals - they also play a role in determining the global structure of the multiverse even at the largest distance scales.
That maybe true, but first we should answer the question if the multiverse really exist or are images in our mind.

Black hole quandary

Black holes are extreme warps in spacetime whose powerful gravity prevents objects that fall into them from escaping.
Black holes (a better name is black star) are very heavy small objects. In some sense they are much heavier and much smaller than our Sun.
As such they provide an ideal testing ground for physics involving strong quantum and gravitational effects.
Black holes are very tricky objects to test. Direct measurements are not possible.
A particular thought experiment about these entities reveals where the traditional way of thinking about multiverse goes of track, thereby making prediction impossible.
Thought experiments can never be used as an argument how the real physical world operates.
The reader is adviced to read the real article.
Even before the black hole has completely evaporated, the book's information starts to slowly leak out via each piece of Hawking radiation.
A black hole (black star) is maybe not completly black i.e. does not loose any energy, this does not mean that we can identify any relation between what formed the black hole and what escapes. To claim such a relation in no way can be physical established.
You might think that the information is simply duplicated: one copy inside and the other outside.
It is physical impossible to copy a book inside a black hole.
Such a solution, however, is impossible.
That is correct, but the argument in the article is wrong.
In quantum mechanics, the so-called no-cloning theorem prohibits faithful, full copying of information.
It is much simpler. copying is physical impossible

In the final part of this paragraph two observers are introduced: One distant and one falling into the Black Hole.IMO not much practical physical information can be learned from both.

Cosmological horizons

The horizon exist because space is expanding exponentially and objects further than this cutoff are receding faster than the speed of light so any message from them can never reach us.
If some objects can recede faster than the speed of light than in principle other objects can recede even faster. This in principe allows the fastest moving object to influence the slower moving object, which is a form of communication.
The situation therefore is akin to a black hole viewed by a distant observer.
A distant observer can emit light/photons towards a black hole, but the black hole can not transmit nothing back towards the observer, as observed by the observer. As such no communication is possible.
The answer is that the creation of bubble universes is probabilistic, like any other process in quantum mechanics.
Again the same question: are there bubble universes? Yes, No or we don't know?
When I study the text almost everything is possible.
The multiple universes in this case do not all exist simultaneously in real space - they coexist only in "probability space",
That is in my mind?
that is as possible oucomes of observations made by people living inside each world.
I do not call this science. Hopefully, some people in an other world agree with me.
the multiverse starts from some initial state and evolves into a superposition of many bubble universes.
If you can not clearly specify what these physical initial conditions are and what the physical processes are that create the other universes you do not have much of a theory.
Without these descriptions these thoughts are more like brain teasers.

The realalm Beyond

To know if this idea is correct, we would want to test it experimentally.
That is IMO impossible. Hopefully I'm wrong.
The multiverse could lead to a small amount of negative spatial curvarure in our universe - in other words, objects would travel through space not along straight lines as in flat cosmos but along curves, even in the absence of gravity.
In our universe (our is a misnomer) this is impossible to test experimentally because the experiment itself is the cause of gravity.
If we were inside one such bubble, space should likewise appear to us to be bent.
How do you know that you are inside a bubble?
All of this is very soft science and that reasoning is already too strong.
Evidence so far indicate that the cosmos is flat, but experiments studying how distant light bends as it travels through the cosmosare likely to improve measures of the curvature of our universe by about two orders of magtitude in the next few decades.
How do you perform such experiments?
Scientists are, however, far from certain if we will detect such signals.
I agree.
I and other physicists are also pursuing the quantum multiverse idea further on a theoretical level.
As I already indicated many times: thought experiments in physics should be avoided to unravel physical laws.
What is time and how does it emerge.
Time is not something. The true question is: how did the universe emerge in the first place? What is it 'origin'?
Time according to this notion, is an "emergent concept" that arises from a more fundamental reality and seems to exist only within local branches of the multiverse.
Time has nothing to do with the multiverse.


Reflection 1 - A theory versus a law

Before you can start with a theory normally we start with making observations. These observations to some extend are identical but also there are differences.
Now there are generally speaking to path to follow. The most important issue is when we have laws we can also make predictions.
In the case of the inflation theory this is not possible (my guess).


Reflection 2 - The reality

To unravel the physical laws we need observations. But does that mean when there are no humans and no observations that there are no physical laws, in the sense that the trajectories of the planets around the Sun are not stable? Humans, our observations, have nothing to do with this. Each star, each planet, each object at any specific moment in time has a specific state, independent of our existance. Each object also includes each electron, each quark and each photon.
Generally speaking performing observations also changes what is measured specific when change is involved. This is true at macroscopic but also at microscopic level. For objects at rest this is not the case. At the instant when the cat dies the cat is dead independent if I observe this event directly or look later.

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Created: 1 June 2017

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