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LISA

The concept of LISA (Laser Interferometer Space Antenna), a space-based gravitational wave detector, has been studied jointly by the European and US space agencies ESA and NASA for 20 years. The planned interferometric gravitational wave detector should be composed of three satellites, positioned to form a triangle, with each side 2.5 million kilometers long. While called eLISA for some time, the project named LISA is expected to launch in 2034.

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Definitioner

eLISA

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LISA

Über 20 Jahre wurde LISA (Laser Interferometer Space Antenna) als Konzept eines weltraumbasierten Gravitationswellendetektors gemeinsam von den europäischen und amerikanischen Weltraumbehörden ESA und NASA voran getrieben. Es soll ein interferometrischer Detektor aus drei Satelliten, angeordnet in einem Dreieck mit 2,5 Million Kilometer Kantenlänge entstehen, welcher vom Weltraum aus nach Gravitationswellen suchen soll. Zwischenzeitlich eLISA benannt, heißt das Projekt wieder LISA und soll 2034 starten. LISA-Website

Laser Interferometer Space Antenna (LISA)

Laser

Abkürzung für "Light Amplification by Stimulated Emission of Radiation", zu deutsch etwa: Lichtverstärkung durch stimulierte Strahlungsaussendung. Verfahren zur Erzeugung sehr konzentrierten, starken Lichtes mit fester Frequenz, das in Form einer sehr gleichförmigen elektromagnetischen Welle ausgesendet wird. Dabei haben alle ausgesendeten Wellen jeweils zur gleichen Zeit ihre Maxima und Minima ("kohärentes Licht").

Laser Interferometer Space Antenna

Siehe LISA

wave

In a general sense: any travelling pattern, whether or not it involves matter being transported as well. Simple examples are water-waves - wave crests and troughs travelling over a water surface, and a Mexican wave in a football stadium, with fans alternately standing up and sitting down - the pattern moves throught the stadium, not the fans themselves.

An especially simple form for a wave is a sinus wave, a regular pattern of wave crests and troughs.

triangle

In a plane and other flat space: Geometrical object consisting of three points ("vertices") with three connecting straight lines. The definition can be made more general, in a way that applies to curved spaces, as well: A geometric object consisting of three points ("vertices") connected by three segments of geodesics.

time

It is a fact of life that not all events in our universe happen concurrently - instead, there is a certain order. Defining a time coordinate or defining time, the way physicists do it, is to define a prescription to associate with each event a number so as to reflect that order - if event B happens after event A, then the number associated with B should be larger than that associated with A. The first step of this definition is to construct a clock: Choose a simple process that repeats regularly. (What is "regular"? Luckily, in our universe, all elementary processes such as a swinging pendulum, the oscillations of atoms or of electronic circuits lead to the same concept of regularity.) As a second step, install a counter: A mechanism that, with every repetition of the chosen process, raises the count by one. With this definition, one can at least assign a time (the numerical value of the counter) to events happening at location of the clock. For events at different locations, an additional definition is necessary: One needs to define simultaneity. After all, the statement that some far-away event A happens at 12 o'clock is the same as saying that event A and "our clock counter shows 12:00:00" are simultaneous. The how and why of defining simultaneity - a centre-piece of Einstein's special theory of relativity - are described in the spotlight topic Defining "now". With all these preparations, physicists can, in principle, assign a time coordinate value ("a time") to any possible events, and describes how fast or how slow processes happen, compared to that time coordinate.

space

In a strict sense: Space as we know it from everyday life: the totality of all locations in which objects can sit, with three dimensions. In a more general sense used by mathematicians, all kinds of sets of points are spaces - a line for instance, which has but a single dimension, or a two-dimensional surface, but also higher-dimensional spaces. Also, in such more general spaces, geometry can be different from the standard Euclidean geometry taught in high schools - such spaces can be curved.

LISA

Laser Interferometer Space Antenna (LISA)

Laser Interferometer Space Antenna

See LISA

interferometric gravitational wave detector (interferometric detector)

Gravitational wave detector that utilizes interference between light waves to detect minute changes in distance effected by a passing gravitational wave. Some of the physics behind interferometric detectors can be found in our spotlight topic Catching the wave with light. Exmples for interferometric detectors are GEO600 and the LIGO detectors.

gravitational wave detector

Currently, scientists world wide are attempting the direct measurement of gravitational waves reaching us from the depths of space. They are mainly using two types of detectors: interferometric detectors like GEO600 and the LIGO detectors, and resonant detectors. For more informations about gravitational waves, please consult the chapter Gravitational waves of Elementary Einstein.

eLISA

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LISA

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