too many hertz
Petahertz?? maybe LISA will look for picohertz signals!!
In other space news today, the boffins in charge of the European Space Agency's LISA Pathfinder mission have wrapped up the final results for the space-based gravitational wave dry run. The Pathfinder carries a pair of 2 kg free-falling cubes, separated by 38 cm and linked with lasers.The masses move relative to each other in …
So "Must improve initial vacuum" gets added to the to do list.
Which is sort of the point of a "pathfinder" mission.
These are excellent results for a precursor mission but 2034? That said the US project of testing relativity with perfect glass spherical gyroscopes on orbit took more like 50 to get all the tech developed.
Impossible to get a perfect vacuum on Earth, so instead make an imperfect seal so those gas molecules eventually find the gap and escape. Then your only noise would be virtual particle pairs being created and annihilated...
"So what is the pressure of the solar system..."
Depends when and where you measure it. But Wikipedia says the pressure around Earth is a few nano-pascals. Interstellar space is rarely emptier than 1 particle per cc, and at 2.7K that works out at ~1E-17 pascals.
plus the random atoms and other doodads getting back in of course - given that space isn't a perfect vacuum.
True, but the odds of something getting IN a tiny gap in an object probably less than a meter across are minuscule versus the odds of something that's bouncing around like crazy inside it getting OUT. Meaning you will eventually attain a perfect vacuum, which appears to have happened here.
Even if something defies the odds and gets in it'll leave pretty quickly via the same "bouncing around like crazy" process and restore your perfect vacuum. I'll bet the odds of a gas molecule getting in to spoil your perfect vacuum are probably less than the odds of a cosmic ray ripping through and upsetting the computers, or a micrometeorite tearing in one end and out the other and destroying it.
The full scale version of this will use fully separate satellites (rather than two masses inside an enclosure). In fact, the full sized LISA will be formed of three satellites 5 million km apart, so they're just going to have to deal with space not being as perfect a vacuum as they might like.
Indeed, even 1uHz = 11.6 days, 1nHz = 31.7 years period. Of course you could have 800pHz as around 40 years and still be well within advertising standards...
Of course it might also be related to the time-derivative of gravity (units anyone?!) where it may be something like 1pico-g per second or similar.
Ever since this project was announced, I can't help but think it's a sequel to the M+M experiment to find the ether.
I think there's a good justification for looking back at some of the ideas previously dismissed as "wrong" to see if they might in fact have had some germ of sense in them ?
A bit like the current vogue for looking back at old medicines for new applications .....
It's interesting that you're comparing it to Michelson-Morley, because the actual apparatus is pretty similar in design, a pair of long 'corridors' with a mirror at the end, down which a laser is shone. The time it takes the laser to go from one end to the mirror and back can be measured precisely by looking at the interference pattern it creates with the out-going light.
M&M were using a right-angled interferometer to try and detect changes in the speed of light. LIGO are using a pretty similar setup (although more precise), to measure changes in the length of the arms of the experiment caused by passing gravity waves. If M&M had access to the same equipment they might have interpreted the data as being small fluctuations in the speed of light.
We're pretty sure that what LIGO is detecting are gravity waves because they match up with events that we can detect with other means. For example, the collapse of two neutron stars produced gravity waves detected by LIGO (and VIRGO), gamma rays detected by Fermi and INTEGRAL and lower energy EM rays detected by a whole host of different instruments.
Are they going to use lasers to keep things in line with that as well ?
Humanity is truly a thing of wonder. On the one hand, we have people capable of thinking of, designing and creating wondrous things like LISA, and on the other hand we have . . . let's not go there.
Thumbs up for boffins, once again !
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