BBC Horizon: What is Reality? (and will the holometer see it?)

January 21, 2011

Last time I commented on a BBC Horizon program it was quite popular so perhaps people will be interested in the latest one entitled “What is Reality?” which aired in the UK this week.

I thought the title did not sound promising but it turned out to be a whistle stop tour through a number of interesting current ideas in theoretical and experimental physics. It started with Jacobo Konisberg talking about the discovery of the Top quark at Fermilab. Frank Wilceck then featured to explain some particle physics theory at his country shack using bits of fruit. Anton Zeilinger showed us the double slit experiment and then Seth Lloyd showed us the worlds most powerful quantum computer, which is not very powerful. Lloyd has some interesting ideas about the universe being like a quantum computer which I encorporated into my FQXi essay, but somehow I dosed off at that point in the program so I will need to watch it again 🙂

Lenny Susskind then made an appearance to tell us about how he had discovered the holographic principle after passing an interesting hologram in the corridor. The holgraphic principle was illustated by projecting an image of Lenny onto himself. Max Tegmark then drew some of his favourite equations onto a window and told us that reality is maths before he himself dissolved into equations.

The most interesting part of the program was a feature about an experiment to construct a holometer at Fermilab described by one of the project leaders Craig Hogan. The holometer is a laser inteferometer inspired by the noise produced at the gravitational wave detectors such as LIGO. It is hoped that if the holographic principle is correct this experiment will detect its effects. Some sceptisicm might be fair dues, but it has to be worth trying. There is info about the holometer here.

I can find the program on Youtube but I wont link because I don’t know if it is an official version that will stay, or whether it is available everywhere or just limited to the UK.

Horizon: Before the Big Bang

October 15, 2010

This week the BBC showed a program in their long running “Horizon” series about the question “What came before the Big Bang?”  Here is the gist of the message: A few years back cosmologists accepted that time did not exist before the big bang, so the question did not make sense. The universe along with time itself just started to exist and has been evolving nicely ever since. But now cosmologists are forming all kinds of theories that do put something before the big bang to explain how and why it happened.

So here is a list of the scientists that featured and the theory they adhere to:

  • Andrei Linde: Multiverse inspired eternal inflation
  • Param Singh: Big Bounce due to repulsive gravity at small distances
  • Lee Smolin: Black Holes spawning baby universes
  • Michio Kaku: Vacuum fluctuation from empty space
  • Neil Turok: Colliding Branes
  • Roger Penrose: The future is empty expanding space = a new big bang
  • Laura Mersini Houghton: String cosmology

Each of these ideas has been around for some time and has been worked on by several people. The individuals mentioned here are not necessarily the ones who invented them. The Penrose theory is an exception in that it is a new idea that features in his next book.

In the program each of these scientists was interviewed while they tried to solve one of those  wooden puzzles

The obvious conclusion to draw is that there are a lot of viable theories out there which cannot all be right. Each of the scientists seemed to have quite a strong belief in the theory they supported, but they would all acknowledge that more experimental input is needed to resolve the question. All of them are driven by a philosophical argument that temporal causality must hold absolute so some prior cause of the big bang is needed.

Along with all the theorising and philosophising, a couple of experiments were mentioned which they think might help test these different hypothesis. The first was LOFAR, a low-frequency radio telescope array that may detect background remnants from the big bang. The standard prediction is that it will be white noise, but anything else could be a clue that separates different theories, prepare your predictions in advance please. The second experiment was the more familiar LIGO and its space bound successors LISA. These may be able to detect a gravitational wave remnant from the big bang that could also have a distinctive signature. It is hoped that either of these experiments may see past the wall of last scattering from which the cosmic microwave background emerged to provide information from an earlier time.

Personally, I don’t accept the philosophical need for something before the big bang and I don’t particularly like any of the theories mentioned. I think it is more likely that there was no space or time prior to big bang singularity which itself is a high temperature and density phase with no fixed topology or geometry for spacetime. I am not alone in preferring theories that do not require time to extend before the big bang, but the program has selected those that do. Where was Hawking’s view for example?

I think that explaining the universe requires us to look at ontological causality rather than temporal causality and the big bang is just one feature of the universe, not the reason for its existence. Although the experiments mentioned and others may throw some light on the nature of the big bang, we first need a better understanding of quantum gravity. There is still scope for theoretical developments that may help even before the experiments bear fruit. Even if you favour the string theory/M-theory route to quantum gravity (as I do), a better understanding of their foundations is required before we can hope to answer these questions about cosmology.

Despite that, I don’t think it is wrong to explore a wide range of cosmological ideas of this kind provided they have some good mathematics behind them. It is time for science to start trying to answer such questions. They will have to be looked at from all angles, philosphical, mathematical and experimental if we want to get the right understanding.

For the record I thought this was a good Horizon program, some of their physics/cosmology episodes lately have been a bit empty and ill-conceived. The position was too one-sided, but well researched. I’m glad they did not make the mistake of mentioning the LHC as if it was likely to resolve these questions, but did mention some other experiments that stand a better chance.  

If you missed the program or it is has not yet aired in your country, I dare say you will find it on the web using Google video search. I wont provide any links because I don’t know which if any are legal copies, or how long they will remain available, or whether the same links will work everywhere.

Why No Data from Gravitational Wave Detectors? (ICHEP)

July 24, 2010

When I was a postgraduate student at the University of Glasgow I was sometimes taken down into the basement to see a remarkable experiment. It was a Gravitational Wave Detector and at that time in 1982 it was the state of the art. They never recorded any positive signal but since then some more impressive GWDs have been constructed including the two LIGO detectors and VIRGO which have arms several kilometers long. 

One talk at ICHEP that I could not see because it was not webcast was “Gravitational wave detectors: First astrophysical results and path to next generation” by Fabien Cavalier. The slides end with a nice quote from Kip Thorn who has been one of the major players in getting LIGO up and running:  “[I]nterferometers should detect the first waves in 2001 or several years thereafter (…)” It is now 2010 and still no gravitational waves have been detected.

To be fair to Kip Thorn we need to quote at least the full sentence from which this quote was taken. We find it in gr-qc/9506086: “If the source estimates described in this review article are approximately correct, then the planned interferometers should detect the first waves in 2001 or several years thereafter, thereby opening up this rich new window onto the Universe.” So the fair interpretation is that the estimates of gravitational waves used in 1995 were not approximately correct. LIGO and VIRGO have set upper limits on how many gravitational wave sources there are. These are the “First astrophsysical results” from the title. Unfortuneatly nobody ever got a Nobel Prize for negative observational results even though they can be very important constraints for theorists.

The most promising sources for GWDs are inspiraling black hole pairs of neutron stars. These would produce a very characteristic signature in the detectors.