PuK - Process Technology & Components 2024

Vacuum technology
Vacuum systems
Tracking the Big Bang
Vacuum Systems for technology development
in gravitational wave detection
Prof. Dr. Oliver Gerberding, Jens Grundmann, Dr. René Wutzler, Dr. Artem Basalaev
How did our universe come into being?
What is our universe made of?
And what events occurred during the
creation process? These and other
questions are on the minds of astronomers
and physicists around the
world today. To answer these questions,
we need information about
the dark objects in our Universe and
about the time close to the Big Bang,
about 13.8 billion years ago. But how
do we get information about objects
that we cannot see and therefore
cannot observe with electromagnetic
radiation? How is it possible
to observe objects and events close
to the Big Bang, at a time when the
universe was opaque? One carrier
of such “old” information is what we
call gravitational waves.
As early as 1915, Albert Einstein described
the influence of mass on space
and time, or spacetime for short, in his
general theory of relati vity [1]. Masses
bend spacetime, which in turn affects
the motion of masses, describing the
phenomenon of gravity. The propagation
of spacetime distortions caused
by accelerated masses is now known
as gravitational waves, and they produce
tiny changes in distance at great
distances from their source. Although
Einstein developed the theory of the
existence of these gravitational waves
in 1915, he assumed at the time that
we would not be able to detect them
on Earth. In 2015, scientists succeeded
in detecting exactly these gravitational
waves [2]. With the help of the
LIGO (Laser Interferometer Gravitational-Wave
Observatory) in the USA,
the collision of two black holes, both
many times the mass of our Sun, was
detected. This collision occurred at a
distance of 1.3 billion light-years from
Earth, making it possible to observe a
cosmic event that took place 1.3 billion
years ago. Since then, more than 100
such events have been recorded [3].
How can we think of gravitational
waves? A simple analogy is a large,
still lake into which a stone is thrown.
Waves are created at the point where
the stone hits the surface of the water.
These waves slowly lose strength
with distance from the point of impact,
so that the waves are barely
noticeable on the shore of the lake.
If this observation were applied to
space, the lake would be our universe
and the rock would symbolize a disturbance
of space-time by an accelerated
mass, such as a moving star or a
collapsing black hole. We would hardly
notice the effect in terms of gravitational
waves at our measuring position,
the Earth as an analogy to the
shore of the lake. This is because,
in addition to the distance from the
events, space-time is very rigid and
much less susceptible to oscillation
than water. This means that only extreme
events, such as the merging of
black holes, can generate measurable
gravitational waves.
The distance changes caused
by gravitational waves are extremely
small. For example, a gravitational
wave caused by the merging of black
a second. These tiny measurements
also place special demands on the
measurement technology to be used.
The central property of special
relativity, that the speed of light is
constant for any observer, was demonstrated
by Michelson and Morley
using a Michelson interferometer.
The principle on which this instrument
is based is laser interferometry
[4]. Such laser interferometers
are also used to detect gravitational
waves, as they can measure tiny
changes in distance extremely well.
The special challenge of this method
is the L-shaped arrangement and the
longest possible optical paths (called
arms) of infrared laser light. Long
arms amplify the effect of the gravitational
wave so that the changes in
distance can still be detected. The laser
light is directed into these arms
by semi-transparent mirrors, reflected
at the end by more mirrors, and
returned to its point of origin. There,
the light waves are superimposed (interference).
Interfering, i. e. superimposed,
waves can amplify each other if “wave
crest meets wave crest” at the same
holes in the Milky Way would change wavelength (constructive interference).
the distance between the Sun and the
Earth by only the diameter of a hydrogen
atom. Moreover, for many of the
objects we observe today, this change
in distance lasts only a thousandth of
Or, when the “wave crest and
trough” meet, extinction occurs (destructive
interference). In the experiment,
the system is set up so that no
light is visible at the output. When a
Fig. 1: Screw pump and magnetically levitated turbopump from Pfeiffer Vacuum
42 PROCESS TECHNOLOGY & COMPONENTS 2024