Date: May 6, 2012
Title: Encore: Are There Alternative Universes?
Podcaster: Stuart Clark
This podcast originally aired on November 18, 2010
http://365daysofastronomy.org/2010/11/18/november-18th-are-there-alternative-universes/
Description: Are there alternate universes? If so, are they merely far away or in different dimensions altogether?
Bio: Dr Stuart Clark is an award-winning astronomy author and journalist. His books include The Sun Kings, and the highly illustrated Deep Space, and Galaxy. His next book is Big Questions: Universe, from which this podcast is adapted. Stuart is a Fellow of the Royal Astronomical Society, a Visiting Fellow of the University of Hertfordshire, UK, and senior editor for space science at the European Space Agency. He is also a frequent contributor to newspapers, magazines, radio and television programmes. His website is www.stuartclark.com and his Twitter account is @DrStuClark.
Intro Sponsor: “This episode of 365 days of astronomy is sponsored with thanks to all non-US contributors for showing us that the night sky is something we can all share.”
Outro Sponsor: “Additional sponsorship for this episode of 365 days of astronomy was provided by iTelescope.net – Expanding your horizons in astronomy today. The premier on-demand telescope network, at dark sky sites in Spain, New Mexico and Siding Spring, Australia.”
Transcript:
ARE THERE ALTERNATE UNIVERSES?
Hello I’m Dr Stuart Clark, astronomy author and journalist. Today I’d like to explore the question: Are there alternate universes?
It must rank as one of the most famous cases of animal abuse in history; thankfully it’s an entirely fictional thought experiment. ‘Schrödinger’s cat’ is the idea that a cat is put in a sealed box with a device containing a radioactive atom that has a 50-50 chance of decaying within an hour. If the atom decays, a flask of poison is broken and the cat dies. In 1935 physicist Erwin Schrödinger considered that, although quantum theory could predict the behaviour of particles, it could not be a true description of reality because it allowed particles to possess contradictory properties until they were measured. Schrödinger asked how the contents of the box could be described at the end of the hour before somebody peeped inside.
The condition of the cat depends upon whether the radioactive atom has decayed or not. Quantum theory can construct an equation that perfectly describes the radioactive atom in a state that represents both decayed and yet-to-decay possibilities. But must the cat be thought of as simultaneously alive and dead until the box is opened? This leaves us with another dilemma: what happens to the ‘unused’ state of the atom, the alternative possibility that was not observed? Did it simply cease to exist when the box was opened?
Physicist Niels Bohr thought the alternative state just vanished. In 1927 with Werner Heisenberg, he decided that prior to the observation the quantum system was in a mixed state, a ‘superposition’ as it’s termed, of all possible outcomes and that measurement creates reality. Known today as the Copenhagen interpretation, it posed a fundamental problem that verged on philosophy: does quantum theory describe reality or is it just a mathematical trick that gives the right answer?
In 1957, American physicist Hugh Everett proposed we take quantum theory at face value and believe that its mathematics does describe reality and all outcomes must be played out somewhere. Everett had no idea where these alternative realities would be, but in one ‘universe’ the cat would live; in another it would die. Our own Universe meanders from one quantum decision to the next, tracing just one of a multitude of paths through reality.
In the 1970s, physicists considered this ‘many-worlds’ interpretation, because they were starting to use higher dimensions in their calculations and they might provide locations for parallel universes, coincident with our own but shifted through a dimension we cannot perceive. The idea of parallel universes is now known as the multiverse.
In 2003, physicist Max Tegmark classified the possible alternative universes into four types. The first comes about because the size of our Universe is suspected to be infinite. We cannot possibly see all of it, because, in the 13.7 billion years since the big bang, light can only have arrived from regions that were once no further than 13.7 billion light years.
If the Universe is infinite then every outcome – however unlikely – is played out somewhere. Any possibility that doesn’t contravene the laws of physics will have happened. Tegmark calls these level I parallel universes.
A slightly different flavour of parallel universe is possible if new universes sprouted away from our own shortly after the big bang because of the way that quantum theory works. It would have set off a chain reaction that continues somewhere in the multiverse today. These comprise Tegmark’s level II parallel universes and inhabit entirely different dimensions of space. The way the forces of nature evolved may be different from ours, and so their strengths could be different and their constants of nature would take different values from ours. Some level II universes will be similar, even identical to ours, whilst others will be vastly different.
In his next category, the level III parallel universes, Tegmark turned his attention to Schrödinger’s cat and Everett’s original suggestion of ‘alternate realities’ in which every possibility is played out.
According to Everett’s many-worlds interpretation of quantum theory, the Universe splits when a quantum decision is revealed – such as when the box in Schrödinger’s cat experiment is opened. This whittling of possibilities into a certainty is known as decoherence and, until the mid 1990s, physicists didn’t know how it happened. In refuting Everett’s ideas, Bohr had talked cryptically about the act of observation being needed to force the quantum system to make its decision, but he failed to define an observer. Was human self-awareness required? Could particles themselves be ‘observers’ by dint of their physical interactions?
Serge Haroche and colleagues used rubidium atoms and microwaves in 1996 to show decoherence occurring as atoms interact with their surroundings. No intelligent observers were needed, just the random interaction of other particles. The conclusion therefore is that particles are indeed Bohr’s ‘observers’ and that the act of observation is equivalent to a physical interaction between particles. This solves the worst aspect of Schrödinger’s cat experiment, namely the period in which the animal is half-dead, half-alive. In fact, the scenario never happens because the interaction of the particles inside the box – the atoms in the cat, the radioactive particle itself, the molecules in the air and in the poison – will mean that if the bottle breaks and releases the poison, the cat will be killed instantaneously, as common sense suggests.
The many-worlds interpretation can be thought of as offering a ‘life after death’ for the timelines rejected in our Universe: a new universe springs into existence to play it out, presumably in some other dimension.
This behaviour is restricted to quantum processes. The only way our conscious decisions could create alternative realities is if somewhere deep inside the brain a decision is based upon a single quantum particle spontaneously changing its state. Flipping a coin is not a quantum process either. It takes place on a larger scale than those at which quantum effects apply. So, sadly, deciding whether or not to finish listening is not going to cause an alternative universe to spring into reality – you may as well stay.
Suppose physicists succeed in finding a theory of everything to describe the ‘superforce’ controlling the Universe that gave rise to the physics of today. They would then face: ‘Why should the laws of physics be as they are?’ The final level of parallel universes rests on the answer to this question.
By 1995, physicists had developed five distinct plausible string theories; then they found something remarkable. Each was a different manifestation of an identical, broader theory, if an eleventh dimension were added. This deeper theory was called M-theory.
Envisaged as a landscape, the valleys contain self-consistent universes and the mountains represent energy barriers between them. Our Universe sits in one of the valleys, but we don’t know which string theory describes it. Other valleys have different laws of physics and constants of nature, and are Tegmark’s level IV universes. Some are similar to our Universe, others not. Many physicists suggest that every combination of laws is tried out in one of these parallel universes.
Will we ever prove that alternate universes exist? Maybe. One method for creating an infinite universe is in a moment soon after the big bang called inflation, when all space balloons exponentially in size. Cosmologists are currently searching for proof that inflation happened. If they find it, they’ll have proof that parallel universes exist, because any form of inflation is thought to create level I types, maybe even level II universes, with different values of the physical constants.
Many observations have been broadly consistent with inflation; if it’s proven to be true, then physicists will have to accept that parallel universes exist. And all of us will have to come to terms with the idea there are many different versions of each of us out there somewhere.
End of podcast:
365 Days of Astronomy
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