SRON_Spectrum_2016

or star, space-time is curved. As a result of this everything in the vicinity
is inclined to move towards the object. That is why the moon orbits
the earth and the earth orbits the sun. Of course we have known
about this phenomenon far longer under the name of gravity. Einstein,
how ever, with his general theory of relativity, was the first to describe
gravity as a curving of space-time.
Ripple
His theory gave rise to a hypothesis that was only proved one hundred
years later. Rapid changes in the quantity of matter at a certain location
cause space-time to ripple, which is comparable with the ripples
that arise if you throw a stone in the pond. These space-time ripples
are known as gravitational waves. They arise, for example, if neutron
stars or black holes collide with each other. As such extreme phenomena
provide insights into how gravity works and the formation of
galaxies, scientists are very eager to study gravitational waves.
With the small blocks experiment, in which SRON is playing an important
role, they hope to be able to do that eventually. Whether that will
actually happen largely depends on the test mission currently in progress.
On 3 December the European Space Agency ESA launched the
LISA/Pathfinder probe. In a piece
According to Einstein of no man’s land in the solar system
it will be examined whether
rapid changes in the
quantity of matter the two gold-platinum blocks on
should cause ripples board can travel through space
completely undisturbed. If that is
in space-time
the case then it will have been
proven that the blocks in space can only be disturbed in one way: by
gravitational waves. That will give the green light for the eLISA mission
in 2034.
are looking for gravitational waves with the help of laser beams.
At these locations two laser beams constantly pass back-and-forth
through tubes that are perpendicular
to each other.
The blocks move in
exactly the same manner Upon their return the beams
through space like
merge. From the light wave
synchronized divers in pattern of the resulting beam
you can see whether a gravi -
a cosmic competition
tational wave has passed
through in the intervening time. That is because the detector is set up
in such a way that the two beams usually cancel each other out. How -
ever, if a gravitational wave passes through the setup then this briefly
deforms the setup as a result of which the waves will no longer cancel
each other out.
New era
It took years before gravitational waves were finally unmasked using
this method. On 11 February 2016 the world of physics threw a party
when researchers announced that the Ligo detector had measured
a passing wave on 14 September 2015. The wave had originated
from two black holes that had merged 1.3 billion years ago. According
to the scientists involved, the discovery marked a new era in physics
and astronomy in which measurements of gravitational waves could
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SRON Spectrum
Why will such a delicate experiment be carried out in distant space?
Although gravitational waves occur everywhere they are very difficult
to observe. That is first and foremost because gravitational waves in -
fluence everything in an identical manner. They can temporarily stretch
a test object but because they stretch your ruler by exactly the same
amount you will not measure the difference.
There are many different ways to circumnavigate this problem. The
Ligo detector in the US and the Virgo detector in Italy, for example,
Simulation of gravitational waves during a collision between black holes (ESA).