Ulteriore prova sperimentale della relatività generale

[lowenz]

E la sonda corroborò la teoria di Albert

http://physicsweb.org/articles/news/11/4/11/1?rss=2.0

A preliminary analysis of data from the Gravity Probe B satellite has confirmed that the Earth's mass distorts the fabric of space and time as predicted by Einstein's theory of general relativity. Although this "geodetic effect" has already been proven with greater accuracy through other measurements, the Gravity Probe team claim that their successful analysis paves the way for using data from the satellite to make a very accurate measurement of a second, much subtler consequence of general relativity called "frame-dragging". However, some physicists are questioning this claim and asking if the final results will be worth the probe’s $700 million price tag.



The Gravity Probe B (GP-B) satellite is a collaboration between NASA and Stanford University and was launched in 2004 with an aim to study two effects predicted by general relativity, a theory first put forth by Einstein in 1915. In addition to the geodetic effect, the theory also predicts that massive bodies will pull space and time along with them as they rotate -- an effect called frame dragging.

Now analysis of the data from GP-B has confirmed the geodetic effect with an accuracy of better than one percent. Although the same effect has already been measured by NASA's Cassini mission, the results indicate that the much subtler frame-dragging effect should be confirmed by further data analysis by the end of this year. Frame-dragging has also been measured before by NASA's LAGEOS satellites with an accuracy of ten percent, and it is currently unclear whether GP-B data will yield a more accurate result.

Gravity Probe B used superconducting quantum interference devices (SQUIDs) to measure tiny changes in the orientations of four perfectly-spherical, quartz gyroscopes as the experiment orbited the Earth for one year. The gyroscopes were housed inside a vacuum chamber and were maintained at 1.8 Kelvin during the measurements using liquid helium. The probe also includes a telescope that was trained on a distant "guide star" to provide a reference direction for measurements on the gyroscopes. General relativity predicts that the frame-dragging effect will cause the direction of the gyroscopes to change by a tiny 0.041 of an arc second.

Prior to launch, however, the satellite suffered numerous delays, and now there is the possibility that the accuracy of its data will not surpass that of other experiments performed before now. "On one level one can say that [Gravity Probe B] is a fantastic triumph of engineering -- nobody has ever done an experiment like this before," Clive Speake, a physicist from the University of Birmingham, told Physics Web. "On the other hand, one can’t do these experiments for fun. We have to wait until the frame-dragging result comes out."

E pensare che c'è ancora qualcuno che non credere alle "fantasiose elucubrazioni di un ebreo".....

[QPDVM^N]

Originariamente inviato da lowenz

E pensare che c'è ancora qualcuno che non credere alle "fantasiose elucubrazioni di un ebreo".....

Questa te la potevi risparmiare, xchè einstain "il nano" ha succhiato sangue
dalla pura razza tedesca !
Se fosse rimasto a gerusalemme, sarebbe rimasto a coltivare noci di cocco ...

[Lucrezio]

Originariamente inviato da QPDVM^N

Questa te la potevi risparmiare, xchè einstain "il nano" ha succhiato sangue
dalla pura razza tedesca !
Se fosse rimasto a gerusalemme, sarebbe rimasto a coltivare noci di cocco ...

Battuta fuori luogo e di pessimo gusto.
3 giorni di sospensione.

[lowenz]

Originariamente inviato da QPDVM^N

Questa te la potevi risparmiare, xchè einstain "il nano" ha succhiato sangue
dalla pura razza tedesca !
Se fosse rimasto a gerusalemme, sarebbe rimasto a coltivare noci di cocco ...

Hai scritto EinstAin

Dammi un motivo valido per ascoltarti, tedescone puro

Mi sa che quello che deve risparmiare qualcosa non sono io

Tra parentesi: la pura razza tedesca è stata spazzata via durante le invasioni barbariche, esattamente come la pura razza latina.

[ChristinaAemiliana]

Un'altra prova!

Relativity passes new test of time

Einstein’s famous tenet of special relativity — that time slows down on a moving clock — has been verified 10 times more precisely than ever before. The result comes from physicists in Germany and Canada, who have timed the “ticking” of lithium ions as they hurtle around a ring at a fraction of the speed of light.


Gerald Gwinner’s colleagues Guido Saathoff and Sergei Karpuk tune the lasers. (Credit: Sascha Reinhardt, Sergei Karpuk, Christian Novotny and Guido Saathoff)

Sit two clocks side by side and, if they are accurate, they will always show the same time. But if one clock is moving rapidly, it will appear to an observer standing next to the stationary clock to be ticking too slowly. This “time dilation” effect, which was predicted by Einstein in his special theory of relativity in 1905, has been verified many times — first to within 1% of predictions in an experiment by Herbert Ives and G R Stilwell in 1938, and more recently by comparing the times of atomic clocks on Earth with those of orbiting global-positioning-system (GPS) satellites.

Such measurements haven’t stopped scientists from suggesting deviations from special relativity, however. For instance, those that are looking for explanations why there is much more matter than antimatter in the universe often invoke a violation of “CPT theorem”, which says that the laws of physics remain the same if the charge, parity and time-reversal properties of a particle are inverted together. CPT violation can justify the observed excess of normal matter, but it might also imply the equations underlying the Standard Model of particle physics, which are based on special relativity, are incomplete.

Testing times

Experiments by Gerald Gwinner from the University of Manitoba in Canada, together with colleagues from various German institutions, give no hint of such deviations from special relativity and thus physics beyond the Standard Model. To test Einstein’s theory, they improved on a technique called laser saturation spectroscopy to measure the time dilation of groups of lithium-7 ions injected at high speed into a magnetic storage ring, based at the Max Planck Institute for Nuclear Physics in Heidelberg.

When at rest with respect to an observer, lithium-7 ions have an electronic transition between energy levels that always takes place at a frequency close to 546 THz — effectively a “ticking clock”. In principle, the amount time dilation changes this frequency for speeding lithium-7 ions could be found by illuminating them with a laser from behind and noting the laser frequency that incites the transition — shown by the ions “fluorescing” or absorbing and re-emitting photons in all directions. In practice, a group of ions in a storage ring have a distribution of velocities, which limits the measurement precision.

Two observers

The researchers avoid this limitation by aiming a second laser into the beam of ions. Although this laser also makes all the ions fluoresce, those in the centre of the velocity distribution receive so many photons that their fluorescence saturates causing a local dip in the spectrum so that ions of only one velocity are “marked”.


The magnetic storage ring at the Max Planck Institute for Nuclear Physics in Heidelberg. (Credit: Max Planck Institute for Nuclear Physics)

Gwinner and colleagues then take the product of the two lasers’ frequencies, which — according to special relativity — should be equal to the square of the transition frequency when the lithium-7 ions are stationary. But because this transition frequency isn’t known accurately enough for their needs, the researchers repeat the experiment for lithium-7 ions travelling at both 3% and 6.4% of the speed of light and check the products are the same.

As expected, the products were indeed the same. But the accuracy of Gwinner and colleagues’ experiment, which is quantified by a “Mansouri-Sexl parameter” of less than 8.4 × 10-8, is over 10 times better than the GPS tests of special relativity. “It means that at the sensitivity level of our experiment, and all others that look for evidence of new physics beyond the Standard Model, is not high enough yet to see anything,” Gwinner told physicsworld.com.


(Si ringrazia lowenz il mito per aver segnalato la notizia )

[MaxArt]

Ecco perché Carl Lewis sembra sempre un ventenne

[nin]

Ma c'era qualche dubbio?

[CioKKoBaMBuZzo]

il dubbio c'è sempre

[xxxyyy]

Certo che se si trovasse una lieve discordanza con la teoria... ci si potrebbe attaccare per costruire una teoria del tutto... ma cosi'... sia meccanica quantistica che relativita' sono super precise, eppure incompatibili... e c'e' tutto quel bordello di meteria e energia oscura la' fuori... miiiiii, che rabbia che mi viene...

[quelarion]

Originariamente inviato da xxxyyy

Certo che se si trovasse una lieve discordanza con la teoria... ci si potrebbe attaccare per costruire una teoria del tutto... ma cosi'... sia meccanica quantistica che relativita' sono super precise, eppure incompatibili... e c'e' tutto quel bordello di meteria e energia oscura la' fuori... miiiiii, che rabbia che mi viene...

beh, considera che questi sono tutti test della teoria classica, difficile tirare fuori qualcosa di veramente importante per una teoria unificata.
Per quel che ne so poi ci sono un sacco di modelli di GR che prendono in considerazioni varianti della teoria, come le teorie f(R) in cui l'azione di Einstein-Hilbert classica è solo un limite al primo ordine nella curvatura.
Quindi discrepanze sarebbero sì interessanti, ma forse non nella direzione delle teorie unificate.
Personalmente mi aspetto buone nuove dall'entrata in funzione di LHC e credo che ora come ora il passo fondamentale sia lavorare ad una teoria seria per la quantum gravity da sola, senza materia. Questo ci farà capire meglio la natura dello spazio-tempo, se sia discreto o meno e quali sono le reali simmetrie che sopravvivono alla quantizzazione.
Fatto questo credo che molti dei problemi del modello standard, come il problema delle divergenze ultraviolette, cioè ad alte energie, verranno risolti. Allora la teoria del tutto sarà più a portata di mano.