Last week, Canada's esteemed Perimeter Institute for Theoretical Physics hosted its big vision conference Quantum to Cosmos. One panel revolved around the question, "What keeps you awake at night?" New Scientist synthesized the seven big questions that emerged from the discussion. Here are two biggies:
How does complexity happen? From the unpredictable behaviour of financial markets to the rise of life from inert matter, Leo Kadananoff, physicist and applied mathematician at the University of Chicago, finds the most engaging questions deal with the rise of complex systems. Kadanoff worries that particle physicists and cosmologists are missing an important trick if they only focus on the very small and the very large. "We still don't know how ordinary window glass works and keeps it shape," says Kadanoff. "The investigation of familiar things is just as important in the search for understanding." Life itself, he says, will only be truly understood by decoding how simple constituents with simple interactions can lead to complex phenomena.Seven questions that keep physicists up at night
What is reality really? The material world may, at some level, lie beyond comprehension, but Anton Zeilinger, professor of physics at the University of Vienna, is profoundly hopeful that physicists have merely scratched the surface of something much bigger. Zeilinger specialises in quantum experiments that demonstrate the apparent influence of observers in the shaping of reality. "Maybe the real breakthrough will come when we start to realise the connections between reality, knowledge and our actions," he says. The concept is mind-bending, but it is well established in practice. Zeilinger and others have shown that particles that are widely separated can somehow have quantum states that are linked, so that observing one affects the outcome of the other. No one has yet fathomed how the universe seems to know when it is being watched.
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If we accept the many-worlds interpretation of quantum mechanics, the universe doesn't know it's being watched; it's just that when you make a measurement, you find out more about which branch of the universe you are in. When you measure particle A, you know something about particle B, not because your measurement changed anything other than your state of knowledge.
I don't know why so many physicists seem to prefer spooky-action-at-a-distance or a magic role for consciousness when many-worlds fits the math just as well.
A set of interesting questions. However, one of them bothers me a little:
*Will string theory ever be proved correct?*
One of the basic tenets of science is the falsifiability of its statements ( http://en.wikipedia.org/wiki/Falsifiability )
A solid scientific theory should provide newly predicted events that can be experimentally measured later on, thus confirming or denying the validity of the model proposed.
A good current example is the Standard Model of particles. Most of the particles predicted by this theory have been *predicted before ever being observed*. Today, the only remaining undiscovered particle is the Higgs Boson. And because scientists don't consider just the working model to be enough, they're now about to kickstart the LHC http://en.wikipedia.org/wiki/Large_Hadron_Collider
But string theorists act a little like priests. They have a beautiful model. Actually not exactly that, it's a mathematical framework for many possible models. Perhaps a great tool based on a new type of post-quantum formalism. However vague and devoid of self-testing premises.
"Will string theory ever be proved correct?" makes about as much sense as "Will God ever be proved to exist?". What model for God? And do most concepts of divine entities ever support a falsifiable test?
I just want to second Joe's comment.
In quantum mechanics, everything is essentially a projection (like a shadow) of an infinite dimensional state vector onto an infinite dimensional space.
In the Copenhagen (spooky action at a distance) interpretation of quantum mechanics, when an observation happens the infinite dimensional vector collapses to include only a version compatible with physics. This includes the two particles having appropriate entangled values.
In 1957, Hugh Everett's PhD thesis proposed the relative state ("many worlds") interpretation of quantum mechanics. He eliminates the collapse, and points out that only some of those shadows obey reasonable mathematical laws. When an event happens that entangles two objects, basically the infinite dimensional vector that describes you + the objects evolves in such a way that there a number of different spaces contain shadows that include you and the objects. Each of those spaces has some compatible combination of the states of those two objects as well. When you measure the state of the objects, you will discover you are in one of those spaces (since they are the only spaces that contain a valid "you" + the objects). In this case "compatible" indicates that the objects have the properly entangled values.
To me it appears that Many Worlds points out that we can eliminate a superfluous law and simultaneously eliminates an open issue (spooky action at a distance) in physics. I don't understand how any physicist focused on quantum mechanics can believe the Copenhagen interpretation, and I can tell you that e.g. Stephen Hawking and the late Richard Feynmann are Many Worlds believers.
This is obviously a very hand-waving description of the relative state thesis, but if you read it (and you can get through the mathematics) you can see that he really does describe why we would get the kind of action-at-a-distance measurements we get from the accepted quantum laws, without having to add a "probability collapse". And he provides a way to think about entanglement that gets the right answers in situations where spooky-action-at-a-distance is just confusing (e.g. Schrodinger's Cat).
"No one has yet fathomed how the universe seems to know when it is being watched."
The most beautiful sentence I have ever read. BB warms my soul and exercises my brain.
I have a question about Many Worlds.
How can we ever know that it is true? If we are "here" and there are other things happening "there" -- how can we ever observe it? Doesn't that push it outside the realm of testable science?
I should point out that "observation" is broadly defined as "interaction with a photon" for the purposes of this conversation.
The universe indeed does not know if it's being "watched." However, things are set into motion once light interacts with matter. Matter that does not interact with light exists only as an indeterminate state, ie. Schrodinger's cat.
And The Bohm interpretation takes care of the suspect spooky action without introducing a totally untestable and somewhat dizzying concept such as the universe constantly breaking off into infinite versions of itself.
But that guy was a commie, so forget him!
"It is written on the limitless constellations of the celestial heavens, on the depths of the emerald seas and on every grain of sand in the vast deserts that the world which we see is an outward and visible dream of an inward and invisible reality." - ancient Sufi saying.
"No one has yet fathomed how the universe seems to know when it is being watched."
I'd just like to mention that many spiritual/relgious groups/individuals of long past have entertained the notion that reality is dual in nature: comprised of the 'known' and the 'unknown'. The 'known' being our material world and the 'unknown' being the underlying energy that sustains the physical form. This energy has both awareness and extreme intelligence.
It is this energy that can be called God or the universe.
At one time this energy had no physical form, but at some point it manifested itself physically as the universe we know and live in.
Everything that exists in our universe is comprised of this energy (the 'unknown'). While 2 physical objects may appear to be separate or unconnected, they are actually one and the same and are connected by their single source of energy. Hence the reason why you've heard the spiritual saying "everything is inter-connected" or "everything is one".
Interestingly enough, the universe is able to perceive itself through physical life forms. For example, take human beings (the most complex creatures we know of in our universe), the universe sees through our eyes, hears through our ears, and basically just experiences our joys, failures, fears, and realizations.
Whenever "we" observe something, the universe is essentially observing itelf (through us). If you think about it, it does actually explain a lot of weird things. Like how ideas seem to spring up at the same time all over the world and how the universe knows when it is being observed.
Enlightened individuals are able to remove "human excess baggage" like ego and pain body, and thus connect to this whole single energy. Great knowledge and insight can be obtained this way. I truly believe that the greatest and most intelligent people in history were able to do just this.
The Bohm Interpretation (http://en.wikipedia.org/wiki/Bohm_interpretation) has two versions: the non-relativistic version, which is known to be false (see the "Comparison to experimental data" on Wikipedia) and the super-generalized relativistic version, which is untestable like Copenhagen and Many Worlds.
There was an early quantum computing result that I thought invalidated hidden variables (beyond Von Neumann's proof that hidden variables can't explain QM which apparently Bohm invalidates). If I find it I'll post back here.
The short answer is no, Many Worlds/Relative State is not testable to my knowledge. When Everett was asked the same question, his reply was something like "when quantum theory is disproven, then my theory is disproven".
If you come from the perspective that what we see in the "everyday" world is not necessarily representative of the fundamental rules in physics (which is absolutely the case if you accept relativity and quantum theory), then IMO MW is just significantly simpler than Copenhagen. Copenhagen stipulates a quantum collapse; MW doesn't need it. When you start thinking about complex entangled problems, from what I can see Copenhagen gives you almost no ground to stand on to predict results; with MW it is much more straightforward.
In fact, if you're willing to accept subjective rather than objective results, you can get experimental evidence for the Many Worlds interpretation. I don't recommend it, though:
MW says that the whole quantum field keeps evolving, which from our perspective implies all worlds possible according to quantum mechanics occur. So, many versions of you are continually created (from your perspective, in fact it's just one evolving quantum field). You only experience the worlds in which you remain conscious.
So, set up a bomb, guaranteed to obliterate you if it goes off. Set the trigger on the bomb to go off when a radioactive atom decays. According to MW, from your perspective the bomb would never go off, which at some point becomes huge evidence in favor of MW, since it becomes exceedingly unlikely that the atom would remain stable so long.
Unfortunately, from the point of view of anyone not next to the bomb, you blow up in a timely way.
To take that further, virtually any event that kills you is avoided in some quantum world. So, for your evidence, I invite you to think back on this when you're 2,000 years old, and the unlikely sequence of events that led you to that ripe age. All the versions of you that die before then of course won't think back on this, for obvious reasons.
Google for "quantum immortality". Remember, this is not necessarily wishful thinking, even if you believe it to be true. The most likely things that would keep you alive beyond a certain point are probably painful and depressing rather than something to think wishfully about.