The Economist has an article this week entitled To catch a gravitational wave. It’s about the proposed LISA satellite experiment designed to measure gravitational waves, with a much greater sensitivity than LIGO. According to the article, what would you guess is one of the main goals of the LISA experiment? Exactly, like most other ambitious experiments, it will solve the problem of how to test string theory:
[LISA] could allow scientists to examine the validity of string theory, which says that there are more than four dimensions to space-time and that the extra dimensions are hidden. String theory has come under fire because its predictions have so far proved untestable. The normal version has it that these dimensions are curled up in strings that are smaller than the known elementary particles. However, in some versions strings form very long “superstrings” that stretch across the universe. These superstrings form loops and vibrate, radiating gravitational waves; they can also crack like whips, sending bursts of gravitational waves towards Earth. “Seeing direct evidence of strings would be as important as discovering that the world is made of atoms,” claims Craig Hogan, an astronomer at the University of Washington, who is a member of the international science team for LISA.
The writer appears to be a bit confused about what a superstring is, guessing that it is a really big string (a cosmic string). This is presumably all based on the idea promoted by Joe Polchinski that it is in principle possible to come up with superstring theory models with cosmic scale superstrings, whose effects would be visible through gravitational lensing and gravitational waves. As far as I can tell, this is just another case of the phenomenon that one can get pretty much anything one wants out of string theory, and there’s no reason at all to expect cosmic strings with just the right properties to have been invisible so far, but visible through gravitational wave effects measurable by LIGO or LISA.
Two years ago there was a press release about this from UCSB quoting Polchinski as saying
the gravitational signatures from cosmic strings are remarkable because they are potentially visible even from the early stages of LIGO! That means ‘potentially visible’ over the next year or two.
LIGO hasn’t seen anything, so time was up for this nearly two weeks ago but I haven’t noticed any UCSB press releases reporting that things haven’t worked out.
There was some excitement a year or so ago when a group claimed that an astronomical object might be a single galaxy lensed by a cosmic string. Turned out to just be a pair of nearby galaxies.
LISA is tentatively scheduled for launch nearly ten years from now, so it will be a while before this particular “test of string theory” brings in any results. This past week the 6th Annual International LISA Symposium was held in Maryland.
Just like expt HEP (or even before HEP), it takes years for astronomy to build a new telescope/detector. I don’t blame the science writers for writing about strings (cosmic or super). It does not matter. What matters is that LISA actually gets built and launched. When the results come out, they will be analyzed on their own merits, whatever may have been said initially about any prospective discoveries.
sunderpeeche,
Scientists shouldn’t spout nonsense to non-scientists in order to justify funding their experiments. Besides being dishonest, its threatens their credibility. If the cosmic string hype had been used as the main justification for funding LIGO, before coming up with the money for LISA, funding agencies might very well start asking about what happened to the cosmic strings (“you mean we gave you X milliion dollars for LIGO to test string theory, now you’ve spent it and learned nothing about string theory, but are asking for more for LISA to test string theory???”)
A friend of mine (i.e. not I) worked at Daresbury Lab in the UK, and they gave a tour to journalists, about the van de Graaf and the synchrotron. Next day there appeared an article about the “world’s tallest synchrotron”. Scientists say what they hope to find, and the string theory people will hope for strings.
From Padmanabhan’s new paper :
There is more to gravity than gravitons.
Kea,
Please, don’t get a discussion going here of alternatives to GR. It more or less immediately becomes too depressing for me to try and moderate.
Sorry.
The last part of your blog post is missing, you know, the subjective part. What would your ideal press release for LISA look like?
Peter said: “Scientists shouldn’t spout nonsense to non-scientists in order to justify funding their experiments. Besides being dishonest, its threatens their credibility. ”
But they do and even nonscientists have seen through it.
“Are researchers over-hyping their results, and prematurely, in order to impress the grant-giving bodies? And are they using ‘jargon’ to keep hold of their special status as a secular priesthood and excommunicate the rest of us?”—from “Mad, Bad and Dangerous?; the Scientist and the Cinema” by Christopher Frayling
Grant-giving bodies are impressed when scientists seem to agree on one theory. So funding thrives on conformity. The search for truth thrives on diversity.
Matt,
Most of the article about LISA was fine, I just think the scientists involved shouldn’t be telling the press that the thing will “test string theory”, because it’s just not true.
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BBC Radio 4 has a programme called “Start the Week” in which guests from the humanities, politics and science discuss issues great and small. Over a year ago, Michio Kaku was a guest and talked about his then new book “Parallel Worlds”. You can hear this programme at:
http://www.bbc.co.uk/radio4/factual/starttheweek_20050131.shtml
Kaku waxed all theological about the cosmological implications of string theory (I think), and added gems like: “we physicists are the only scientists who can use the word God and not blush”. About 13 minutes into the recording, one of the guests brought up the awkward problem of experimental verification, at which point Kaku emphatically mentioned that the LISA satellite would provide the necessary data. I’d be interested to hear what people from this blog think of such comments.
I think they should invite Peter onto Start The Week.
People from this blog, and from most of the theory community, know that whatever Kaku says is a steaming pile of baboon crap.
Dear Troublemaker,
Kaku is entertaining. If you critics are right, and things are less complex than the extradimensional landscape and cosmic strings, then physics will be boring.
Better change your scientific attitude. This is a difficult process, so go gently. Start off training yourself to be a pseud by believing one lie each morning before breakfast.
Gradually build up your stamina until you can force yourself to believe six hoaxes a day:
Alice laughed: “There’s no use trying,” she said; “one can’t believe impossible things.”
“I daresay you haven’t had much practice,” said the Queen. “When I was younger, I always did it for half an hour a day. Why, sometimes I’ve believed as many as six impossible things before breakfast.”
– Alice in Wonderland.
Reading that book inspires string theorists (according to testimony in the book “Warped Passages”).
Kaku emphatically mentioned that the LISA satellite would provide the necessary data.
For those interested, I am keeping a post on papers related to the predictions of quantum gravity about the gravitational wave phenomenon. More papers will be added opportunely.
Best wishes,
Christine
sunderpeeche,
You are mistaken – just building and running instruments is a worthless endeavor if their only purpose is to reinforce preconceived notions (witness WMAP 3).
-drl
Indeed yes, if the real purpose of building an instrument (accelerator, telescope, …) is just to have some machine in the lab, to keep the staff employed, then that is worthless. There has to be some scientific goal, and typically those goals are formulated in terms of the theoretical prejudices of the day. Today it’s strings. Don’t know about WMAP 3 ~ they tried to probe the CMB in more detail, and presumably new instruments will keep doing so. Will LHC be worthless if it finds a SM Higgs and nothing else?
The nuclear power and fusion industry does offer an example of overhyped promises, though. Today the knee-jerk reaction is to be suspicious of any new nuclear power plants. It may become so with particle accelerators. (It has already become so?)
sunderpeeche wrote: “Will LHC be worthless if it finds a SM Higgs and nothing else?”
I posted this comment in response to “LHC predictions at Seed”, but a little too late to get a reply. But now that the topic has come up again…. Wouldn’t it be significant if LHC *doesn’t* find superpartners, as evidence *against* super-symmetry at low enough energies to solve the hierarchy problem (which I thought was one of the main arguments for believing in supersymmetry in the first place)?
That doesn’t seem analogous to LISA looking for cosmic strings, though, since I don’t think anyone is really expecting to see any. If a negative result doesn’t make anybody question the theory (who wasn’t questioning it already), then it can’t be called much of a “test”.
I don’t think this has been mentioned in this blog before (apologies if it has), and it’s related to LIGO. The gravitational waves resulting from two black holes colliding can now be calculated! I have heard that in the last year, several groups, including one at NASA, have figured out how to overcome the numerical instabilities and simulate black hole collisions. You can google and find some news reports and a really neat video from NASA. I can’t really find anything about what this means for LIGO and LISA, though.
Peter,
From what I’ve seen the magnitude of these waves is such that for them to be detectable by LIGO, the black holes would have to be relatively nearby, so much so that no one really expects to LIGO to see such a signal while it is running. Don’t know about LISA…
D R Lunsford: “You are mistaken – just building and running instruments is a worthless endeavor if their only purpose is to reinforce preconceived notions (witness WMAP 3).”
I think calling WMAP worthless is a bit strong (disclosure: I was a co-author on a few WMAP-related papers). It’s given significantly improved bounds on various cosmogical parameters and on things like neutrino masses.
However, I do see and agree with your broader point. I remember the NASA press release calling WMAP results “stunning” and “one of the most important scientific results of recent years.” I’m sorry, and I intend no disrespect to the WMAP team, but that’s hype. It was a fabulously well-done experiment, and it did give rise to some mysteries such as the low quadrupole moment, but it essentially confirmed the broad details of what was already suspected. It certainly wasn’t comparable to, say, Rutherford’s experimental discovery of the atomic nucleus in the sense of being a revolutionary, paradigm-shifting result.
I was in early-Universe cosmology for several years, and one of the reasons I switched fields was that I was starting to see the same factors that have distorted particle physics — primarily, too much theory and not enough data (and secondarily, increasing amounts of starry-eyed hype that give a misleading impression of how certain or complete the science really is) — appear in cosmology. It’s not nearly as severe, of course, and in most respects it’s still a very healthy field. But how are we going to, say, get more than a very rough idea of the inflaton potential, let alone make controlled measurements of an inflaton or a dark matter particle in a lab? I have a nagging feeling that CMB and gravity wave measurements, though important and significant, just won’t be enough to give the kind of experimental verification to these theories which is utimately needed in science, and I’m not sure the technology that would allow it will be here any time soon.
(My apologies to Dr. Woit if this is getting too off-topic.)
Peter(s): Frans Pretorius from Caltech (formerly UBC) gave a very nice colloquium at PI, available here , worth checking out.
(also experimenting with html tags, let’s see if it works)
Not quite… in any event it is on page 2, and the title is “Simulation of Binary Black Hole Mergers”.
P. Woit Said:
…for them to be detectable by LIGO, the black holes would have to be relatively nearby, so much so that no one really expects to LIGO to see such a signal while it is running. Don’t know about LISA…
If anyone wants a figure for how nearby, I could shed some light, I was a undergrad researcher at LIGO Hanford during a previous summer. LIGO often measures the detector sensitivity by the range at which it would detect a “typical” neutron star binary inspiral. The LIGO Hanford 4K interferometer currently runs at about 13Mpc. The Virgo cluster is about 15 Mpc away, which is a good place to expect a good number of inspirals.
Of course, Advanced LIGO (the upgrade which will start in the next few years ~07 or 08) will see 10 times farther, and LISA won’t be up until at least 2015, so my money is on LIGO.
“From what I’ve seen the magnitude of these waves is such that for them to be detectable by LIGO, the black holes would have to be relatively nearby, so much so that no one really expects to LIGO to see such a signal while it is running. Don’t know about LISA…”
LISA is guaranteed to see gravitational waves, at least from white dwarf binary systems in our galaxy. So many in fact, that they cannot be resolved and will form one of the important sources of “noise” ( see e.g. gr-qc/0204090).
sunderpeeche said,
Scientists say what they hope to find, and the string theory people will hope for strings.
No, there is an etical code for scientists is sistematically violated by string theorists. These sistematic unethical news are not common in the rest of normal science.
It is so unethical to claim that string theory is falsable as claim that string theory predicted gravity, when is even unable to reproduce GR results from first principles.
Juan R.
Center for CANONICAL |SCIENCE)