what are the implications of negative detection?
24 Feb 2005 16:23:37 UTC
Topic 187946
(moderation:
there are some excellent papers available at www.ligo.org detailing the specifications of the LIGO/GEO instruments and limitations on the data. the increasing sensitivity of the current instruments and the projected sensitivity of advanced ligo or ligo ii point to the possibility of negative detection. there are four schemes or areas of detection that are being developed (please research them before posting here). a negative detection in any one of them would have profound implications. i recommend the book LIGO: Prelude to Revolution by Ed Hatch. for the uninitiated, 'negative detection' refers to the absence of an anticipated signal. if you expect to hear my voice in a room as i speak, but hear nothing, you are startled - you automatically wonder why you do not hear my voice. this is analogous to negative signal detection in gravity wave physics. we expect to observe gravitational waves because current theories predict them, but if we do not, we may need to revise our theories - this is the dilemma facing convention.
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what are the implications of negative detection?
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if i understood the first post right - we are looking for faster than possible pulsars rotations. If we find such a fast pulsar it would render impossible current theories that predict existance of gravitational waves.
If it is not clear i'll try to explain it in other words:
a) current theories that predict gravitational waves do postulate that pulsars cannot rotate faster than X rotations per second
b) if we find at least one pulsar that rotates faster than X it will render current theories impossible in nature
from the above i wonder what the value of X is ?
The fastest a pulsar can
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The fastest a pulsar can rotate theoretically is about 3,000 rps before tearing itself apart. The fastest we (us humans) have seen is about 600 rps. I don't think we're looking for "impossible" pulsars. We're looking at known high-rotation pulsars. Theoretically, high rotation speed pulsars, particularly those in a binary relationship, should generate large amounts of gravity waves. Those waves *MAY* be able to be detected as perturbutations in the time it takes for a laser beam to travel down two 4 kilometer L-shaped arms of the detector. If everything is normal, the two beams arrive back at the same time. If one has been modified by a gravity wave, there will be a difference in time. If my guess is correct, we're looking at differnces in the amount of time and matching that with known pulsar positions.
What are the implications of negative detection? Most likely that we don't have a powerful enough detector, some form of "noise" is hiding the signal, the radiation isn't in a band we're measuring, ad nauseum. In the example in the first post, you may be speaking quite loudly but at a frequency that my hearing can't detect. It doesn't mean you aren't speaking. Just that I'm not listening correctly.
It's quite interesting that no pulsars are known to exist that spin faster than 600 rps. Is there some force, perhaps dissipation of energy by dissemination of gravity waves, that prevent higher rotation speeds? Dunno...
What does it mean if we detect an abberation in the arrival times of the two beams and the detector is not lined up on a pulsar? Does it indicate the possible collision of two dark galaxies? That ought to generate one heck of a gravity wave! Dunno...
Of course, this is all just my opinion. I could be wrong...
There are two secrets to life: 1) Don't tell everything you know...
A most excellent overview of
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A most excellent overview of the project, to be sure!
> The fastest a pulsar can
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> The fastest a pulsar can rotate theoretically is about 3,000 rps before
> tearing itself apart. The fastest we (us humans) have seen is about 600 rps. I
> don't think we're looking for "impossible" pulsars. We're looking at known
> high-rotation pulsars. ......... >
> It's quite interesting that no pulsars are known to exist that spin faster
> than 600 rps. Is there some force, perhaps dissipation of energy by
> dissemination of gravity waves, that prevent higher rotation speeds? Dunno...
Short view;;;;;
Think of the rotation pulsar as one big nucleus with a radius of something like 10's of miles. The centrifugal force from the spinning (yes, I know there is no such thing- it is really centripetal forces.... but for now...) tends to make the pulsar pull apart. But the nuclear forces pull it together. At some size and speed (around 3000 or so rev/sec) the centrifugal force out is greater than any nuclear binding force so it is ripped apart.
Basically it is a balancing act between forces, nuclear forces and inertial forces. Spin something fast enough and it flies apart.
New Scientist article from
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New Scientist article from 22/02/2005....
Fast-spinning star could test gravitational waves
Marj
Marj, Thanks for the article.
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Marj,
Thanks for the article. As usual, it brought new qusetions to mind. For one, why do some pulsars radiate in light and some in x-ray. Is it mass thing?
I'm not sure I agree with Chakrabarty's statement that if LIGO doesn't spot a gravity wave then gravity waves aren't the brake that keeps millisecond pulsars around 600rps. But what do I know.
There are two secrets to life: 1) Don't tell everything you know...
as i understand it - there
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as i understand it - there have been no candidates for any of the four categories for detection (of GWs). now, of course i do not believe we will never detect any GWs - we will, but they will not be as expected. my original point was: non-detection in any one of the four categories implies a required revision in some parts of conventional understanding (theoretical revisions). it is possible some ideas/concepts/theories may have to be thrown out entirely if we never detect any candidate signals in one particular category (with increasing sensitivity such as with advanced ligo or ligo ii). people need to start thinking 'outside the box'. they let their assumptions dictate the directions of their ideas and 'solutions'. it is regrettable that my point was missed entirely by every single reader who cared to respond. younger minds need to be trained to be creative and holistic (plz consult How to Solve It: Modern Heuristics by Michalewicz & Fogel).
please visit http://groups.yahoo.com/group/faraday_group/ and consider joining; we are a mutually inspiring group of determinists with some very interesting ideas!
[Physicist hat on]
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[Physicist hat on]
Negative detection can in fact be as, if not more important than an actual detection. The Michaelson-Morley experiments were amazingly important nondetection events disproving the Aether theory and leading to Special Relativity (or at least wide acceptance of SR, depending on who you read and believe).
Don't assume that negative results would be worthless, they can be as, if not more important than confirmations.
[Physicist hat off]
> [Physicist hat on] >
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> [Physicist hat on]
> Negative detection can in fact be as, if not more important than an
> actual detection. The Michaelson-Morley experiments were amazingly important
> nondetection events disproving the Aether theory and leading to Special
> Relativity (or at least wide acceptance of SR, depending on who you read and
> believe).
Don't assume that negative results would be worthless, they can
> be as, if not more important than confirmations.
> [Physicist hat off]
>
Thanks for the input. I happen to agree with you. Non-detection is essential for refining theorems and search criteria. Non-achievement of goals is not a failure, IMHO.
Are you a physicist? I have some questions that I'd love to ask. One can only go just so far in independent study.
There are two secrets to life: 1) Don't tell everything you know...
> The Michaelson-Morley
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> The Michaelson-Morley experiments were amazingly important
> nondetection events disproving the Aether theory and leading to Special
> Relativity
In fact MM experiment did not disprove Aether theory completely (if you mean by aether the substance like air is for sound waves then yes it was disproved, but if you look at Aether as existance of prefered frame of reference then it was not)
there is a Lorenz Relativity (LR) that explains MM experiment equally well as special relativity (SR) does.
What i wanted to note is that MM experiment did not prove that SR theory is right, other (alternative) theories do exist that also comply with MM experiment results
and here i must agree with senator2 - we should think about what nondetection would mean - what if pulsars do not generate gravitational waves at all ? do we have an alternative to GR theory ready to explain that ?