Time travellers: David Tennant as Doctor Who
with Billie Piper as Rose
Posted on 09/22/2007 8:52:50 PM PDT by bruinbirdman
Science fiction looks closer to becoming science fact.
Parallel universes really do exist, according to a mathematical discovery by Oxford scientists that sweeps away one of the key objections to the mind boggling and controversial idea.
The work has wider implications since the idea of parallel universes sidesteps one of the key problems with time travel. Every since it was given serious lab cred in 1949 by the great logician Kurt Godel, many eminent physicists have argued against time travel because it undermines ideas of cause and effect to create paradoxes: a time traveller could go back to kill his grandfather so that he is never born in the first place.
Time travellers: David Tennant as Doctor Who
with Billie Piper as Rose
But the existence of parallel worlds offers a way around these troublesome paradoxes, according to David Deutsch of Oxford University, a highly respected proponent of quantum theory, the deeply mathematical, successful and baffling theory of the atomic world.
He argues that time travel shifts between different branches of reality, basing his claim on parallel universes, the so-called "many-worlds" formulation of quantum theory.
The new work bolsters his claim that quantum theory does not forbid time travel. "It does sidestep it. You go into another universe," he said yesterday, though he admits that there is still a way to go to find schemes to manipulate space and time in a way that makes time hops possible.
"Many sci fi authors suggested time travel paradoxes would be solved by parallel universes but in my work, that conclusion is deduced from quantum theory itself", Dr Deutsch said, referring to his work on many worlds.
The mathematical idea of parallel worlds was first glimpsed by the great quantum pioneer, Erwin Schrodinger, but actually published in 1957 by Hugh Everett III, when wrestling with the problem of what actually happens when an observation is made of something of interest - such as an electron or an atom - with the intention of measuring its position or its speed.
In the traditional brand of quantum mechanics, a mathematical object called a wave function, which contains all possible outcomes of a measurement experiment, "collapses" to give a single real outcome.
Everett came up with a more audacious interpretation: the universe is constantly and infinitely splitting, so that no collapse takes place. Every possible outcome of an experimental measurement occurs, each one in a parallel universe.
If one accepts Everett's interpretation, our universe is embedded in an infinitely larger and more complex structure called the multiverse, which as a good approximation can be regarded as an ever-multiplying mass of parallel universes.
Every time there is an event at the quantum level - a radioactive atom decaying, for example, or a particle of light impinging on your retina - the universe is supposed to "split" into different universes.
A motorist who has a near miss, for instance, might feel relieved at his lucky escape. But in a parallel universe, another version of the same driver will have been killed. Yet another universe will see the motorist recover after treatment in hospital. The number of alternative scenarios is endless.
In this way, the "many worlds" interpretation of quantum mechanics allows a time traveller to alter the past without producing problems such as the notorious grandfather paradox.
But the "many worlds" idea has been attacked, with one theoretician joking that it is "cheap on assumptions but expensive on universes" and others that it is "repugnant to common sense."
Now new research confirms Prof Deutsch's ideas and suggests that Dr Everett, who was a Phd student at Princeton University when he came up with the theory, was on the right track.
Commenting in New Scientist magazine, Prof Andy Albrecht, a physicist at the University of California, Davis, said of the link between probability and many worlds: "This work will go down as one of the most important developments in the history of science."
Quantum mechanics describes the strange things that happen in the subatomic world - such as the way photons and electrons behave both as particles and waves. By one interpretation, nothing at the subatomic scale can really be said to exist until it is observed.
Until then, particles occupy nebulous "superposition" states, in which they can have simultaneous "up" and "down" spins, or appear to be in different places at the same time.
According to quantum mechanics, unobserved particles are described by "wave functions" representing a set of multiple "probable" states. When an observer makes a measurement, the particle then settles down into one of these multiple options.
But the many worlds idea offers an alternative view. Dr Deutsch showed mathematically that the bush-like branching structure created by the universe splitting into parallel versions of itself can explain the probabilistic nature of quantum outcomes. This work was attacked but it has now had rigorous confirmation by David Wallace and Simon Saunders, also at Oxford.
Dr Saunders, who presented the work with Wallace at the Many Worlds at 50 conference at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, told New Scientist: "We've cleared up the obscurities and come up with a pretty clear verdict that Everett works. It's a dramatic turnaround and it means that people now have to discuss Everett seriously."
Dr Deutsch added that the work addresses a three-century-old problem with the idea of probability itself, described by one philosopher, Prof David Papineu, as a scandal. "We didn't really know what probability means," said Dr Deutsch.
There's a convention that it's rational to treat it for most purposes as if we knew it was going to happen even though we actually know it need not. But this does not capture the reality, not least the 0.1 per cent chance something will not happen.
"So," said Dr Deutsch, "the problems of probability, which were until recently considered the principal objection to the otherwise extremely elegant theory of Everett (which removes every element of mysticism and double-talk that have crept into quantum theory over the decades) have now turned into its principal selling point."
That explains a few things that have happened over the last few years - we got forked in time. ;)
Thanks. Now I am back in the right universe.
1. If new multiverses are spawned off every time that a particle can assume more than one state, then it is not a question of whether or not you survive an accident. It becomes billions and billions of questions such as what happens if a particular electron in a particular atom in your shoulder jumps to a different state at the time your car hits the railing.
2. If multiverses are only spawned when an observation is made, then we had a single universe up until the time that the first sentient being was created. Before then there were no observations, unless we consider God an observer. If we are the only sentient beings, then was the first multiverse spawned when the first intelligent ape was formed? the first homo sapien? the first scientist? the first person to observe a quantum mechanical effect?
3. In most parallel universes when scientists perform the two slit experiment they see what we see: an interference pattern caused by a series of photons going in equal amounts through two different slits. However, in countless other universes there are a bunch of scientists who are still confused about why only 40% go through one slit and 60% through the other. And there is at least one universe where all the photons go through one slit or the other. How confused are they? Can they even do science in those universes? And why did we luck out and have a universe where quantum mechanics makes some measure of sense?
4. If every possible universe is possible then there is a being similar to me that goes from being Hitler-esque in one universe to nothing short of Mother Theresa in another. If the laws of physics require this to be so, then morality is a meaningless concept. No matter how good I am in this universe, I will be required to be evil in countless others thus negating any overall moral effect. If free will is superimposed upon quantum randomness, then it might be that if you averaged all the multiverses the average person would be better than expected due to God's influence ... or worse than average due to God allowing Satan to work his "charms" on all of the beings in all of the multiverses.
This is all quite silly.
Turns us into "projections", but that's better than being turned off, eh.
The double slit Delayed Choice Quantum Eraser is an experiment that has already been done and appears to prove you can change the quantum past without going into another universe.
Sure, but try to find a decent Hamiltonian for H, and then find a good enough basis to express it in...
Let me know when it converges; I won't wait up dinner for you.
Sound of grey_whiskers purring.
Cheers!
But, it is only a ""proposal 
yitbos
One problem, you can’t change your own parallel universe vis TT. So all you get is an infinity of models. Time wasted!
But something seriously weird is happening.
no u don’t because al gore would be President now...
I ain’t got no ideer what in blazin’s you’s tryin’ ta spit outta yer noggin son !
Since I’m not a scientist, I’ve had to think about this for awhile.
Is it possible that the feeling we get of deja vu isn’t really a “I’ve done this before” but a possible nanosecond aligning of the parellel universes where I (all of me) are doing the exact same thing at the exact same time, and a blending of ‘our’ consciousness?
Possible?
Infinitely possible!
But, maybe not.
yitbos
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