Gravitational Waves.

[mfgoode]

Gravitational waves first theorised by Albert Einstein in 1916 seems to be capable of being detected by LIGO and LISA .
It also is supported by string theory which was an elaborate off shoot of General Theory ..


Cosmic Superstrings Might Sing in Gravity Waves

By Tariq Malik [New Scientist]
Staff Writer
posted: 9 January 2007
6:00 a.m. ET


The hunt for elusive gravitational waves has a new target: singing cosmic superstrings that theoretically emit the long-sought waves as they vibrate.

The superstrings are “so light that they can’t have any effect on cosmic structure, but they create this bath of gravitational waves just by decaying,” said Craig Hogan, a cosmologist with the University of Washington (UW).

Gravitational waves, ripples of gravity caused by moving matter as it warps the fabric of space and time, were first theorized by Albert Einstein in his theory of general relativity in 1916, though the phenomena have yet to be observed in real time.

String theory posits that hidden dimensions are tightly wound in strings of elementary particles. An offshoot of this theory suggests that some such strings can form into narrow tubes of energy stretched across vast distances by the expansion of the universe. These theoretical cosmic superstrings, which researchers described as ultra-thin tubes filled with ancient vacuum created in the early universe, can coil into galactic-sized, vibrating loops that emit gravitational waves as they decay into oblivion [graphic].

They might also be detectable using the Laser Interferometer Gravitational Wave Observatory (LIGO) or NASA’s proposed Laser Interferometer Space Antenna (LISA), Hogan added.

“Sensing these vibrations would add the soundtrack to the beautiful imagery of astronomy that we are used to seeing,” Hogan said. “All this time, we have been watching a silent movie.”

Hogan and Matt DePies, a UW doctoral student and visiting physics lecturer, presented calculations for cosmic superstring-generated gravity waves last week at a meeting of the American Astronomical Society in Seattle.

Since gravitational waves are thought to be extremely weak, cosmologists believe that only those generated by massive collisions will be strong enough to be observed.

A black hole smash up, for example, could spew waves of up to a million times the more power than those produced by every galaxy in the universe, researchers said. Hogan added that while some gravity ripples could occur at frequencies perceptible to the human ear, many sources are likely to have extremely low frequencies of 10 to 20 octaves below the range of human hearing.

Mally

[ewmayer]

Dear lord, not more massively-overblown string-theory bullcrap.

By the way, as far as I know, Einstein himself never "predicted" gravitational waves (just like he never "predicted" black holes, the expanding universe or gravitational radiation) - others deduced that they were a natural feature of general relativity. Thankfully for us, his theory was smarter than he was. ;)

[xilman]

Originally Posted by ewmayer

By the way, as far as I know, Einstein himself never "predicted" gravitational waves (just like he never "predicted" black holes, the expanding universe or gravitational radiation) - others deduced that they were a natural feature of general relativity. Thankfully for us, his theory was smarter than he was. ;)

He did, however, recognize that a static universe required a finely tuned magic number and introduced it into his field equations so that they could accommodate a static universe.

When the universe was discovered not to be static, he described his cosmological constant as the greatest error of his life.

Possibly one of the greatest ironies of the twentieth century was the discovery,not long before the turn of the millenium, of "dark energy" which manifests itself as a non-zero cosmological constant!

(And "gravitational waves" is exactly the same phenomenon as "gravitational radiation", but that is a minor semantic quibble.)

Paul

[ewmayer]

Originally Posted by xilman

When the universe was discovered not to be static, he described his cosmological constant as the greatest error of his life.

IIRC the exact quote is "Die grösste Dummheit meines Lebens."

Possibly one of the greatest ironies of the twentieth century was the discovery,not long before the turn of the millenium, of "dark energy" which manifests itself as a non-zero cosmological constant!

...albeit one of the opposite sign (i.e. tending to accelerate the expansion) as Einstein introduced to prevent things from flying apart. For my part, I'm still unconvinced that there is indisputable evidence of an accelerating expansion, but it certainly is a fascinating possibility.

(And "gravitational waves" is exactly the same phenomenon as "gravitational radiation", but that is a minor semantic quibble.)

True enough. I (and apparently many others) prefer to treat the former as a special subclass of the latter, one arising from discrete (typically catastrophic) events and having a clear discrete frequency structure, as opposed to e.g. the continuous "glow" of gravitational radiation from gravitationally dissipative systems like close compact binary objects. Shaking and sloshing as opposed to steady stirring, as it were.

[cheesehead]

Originally Posted by ewmayer

For my part, I'm still unconvinced that there is indisputable evidence of an accelerating expansion, but it certainly is a fascinating possibility.

http://www.astro.ucla.edu/~wright/sne_cosmology.html has some plots from "the latest dataset: Riess et al. (2007)."

From the abstract of the latter:

"We have discovered 21 new Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to trace the history of cosmic expansion over the last 10 billion years. These objects, which include 13 spectroscopically confirmed SNe Ia at z > 1, were discovered during 14 epochs of reimaging of the GOODS fields North and South over two years with the Advanced Camera for Surveys on HST. Together with a recalibration of our previous HST-discovered SNe Ia, the full sample of 23 SNe Ia at z > 1 provides the highest-redshift sample known. Combined with previous SN Ia datasets, we measured H(z) at discrete, uncorrelated epochs, reducing the uncertainty of H(z>1) from 50% to under 20%, strengthening the evidence for a cosmic jerk--the transition from deceleration in the past to acceleration in the present. The unique leverage of the HST high-redshift SNe Ia provides the first meaningful constraint on the dark energy equation-of-state parameter at z >1.

"The result remains consistent with a cosmological constant (w(z)=-1), and rules out rapidly evolving dark energy (dw/dz >>1). The defining property of dark energy, its negative pressure, appears to be present at z>1, in the epoch preceding acceleration, with ~98% confidence in our primary fit. Moreover, the z>1 sample-averaged spectral energy distribution is consistent with that of the typical SN Ia over the last 10 Gyr, indicating that any spectral evolution of the properties of SNe Ia with redshift is still below our detection threshold."

[ewmayer]

Thanks for the link, Richard. I should've been clearer - my reservations are not with respect to the reality of the redshift/supernova data, but that there may be alternative,

The particle physicists in particular have a long history of immediately jumping on exotic explanations for unexplained phenomena: cosmic strings (or what have you) for high-energy cosmic rays (whereas the current most-likely candidates involve high-energy shock-wave/particle interactions), the Casimir-effect/Hawking-radiation for Sonoluminescence (ha, check out the section titled "Shrimpoluminescence" on the same wikipage), et cetera. In the vast majority of such cases - assuming the result itself holds up - more-mundane (which is not to say "uninteresting") physical phenomena are later found to be responsible. But "Cosmic Strings sing a high-energy Cosmic tune!!!!???" makes for a snazzier headline than "It's charged-particle/shock-wave interactions, dummy."

[Uncwilly]

Originally Posted by ewmayer

IIRC the exact quote is "Die grösste Dummheit meines Lebens."

For a bit of personal interest, can you point to some source? I think that by the time that it was quite clear that Hubble was right, that Al was living in the USA. I personally know someone, that as a child, used to visit him and he would read stories to the kids in English.

[ewmayer]

Originally Posted by Uncwilly

For a bit of personal interest, can you point to some source?

It should be in the biography by Abraham Pais, but I haven't had a chance to check for the precise place there. do you have that bio? If not, I highly recommend it. (I see it's now out in paperback, although that's one I consider a "keeper" and wouldn't trade my hardback.)

The last sentence on this German Einstein-Bio page also has the quote the way I remembered it above.