What is the purpose of 'evolved Laser Interferometer Space Antenna (eLISA)' project?
Contents17
- ATo detect neutrinos
- BTo detect gravitational waves
- CTo detect the effectiveness of missile defence system
- DTo study the effect of solar flares on our communication systems
Show answer
Answer: (B) To detect gravitational waves
eLISA (evolved Laser Interferometer Space Antenna) is a planned space-based gravitational wave observatory led by the European Space Agency (ESA).
The project involves placing three spacecraft in a triangular formation in space, trailing the Earth in its orbit around the Sun at a distance of over 50 million km.
These spacecraft will use laser interferometry to measure incredibly tiny changes in the distances between free-floating test cubes inside each spacecraft.
When a gravitational wave passes through, it stretches and squeezes space itself, causing minute changes in these distances — which the laser interferometers can detect.
Gravitational waves were first predicted by Albert Einstein in 1916 as part of his General Theory of Relativity, and they were first directly detected by the ground-based LIGO observatory in 2015 (a discovery that won the 2017 Nobel Prize in Physics).
eLISA is the next step — moving the detection to space, where it can detect gravitational waves of much lower frequencies than ground-based detectors.
Option (a) is wrong — neutrino detection uses different technology (like ice/water-based detectors).
Option (c) is wrong — eLISA has nothing to do with missile defence.
Option (d) is wrong — solar flare studies use different instruments.
Key association: eLISA = space-based + laser interferometer + gravitational wave detection.
LIGO detected gravitational waves for the first time in 2015 and won the Nobel Prize in Physics in 2017, making gravitational wave detection a major current topic when this question was asked.
eLISA represents the next generation after ground-based detectors like LIGO - moving to space allows detection of much lower frequency gravitational waves that cannot be detected on Earth.
The question tests whether students can distinguish between different space-based detection technologies - laser interferometry for gravitational waves versus other methods for neutrinos or solar phenomena.
eLISA Gravitational Wave Observatory
Science And Technology eLISA evolved Laser Interferometer Space Antenna
eLISA: Space-Based Gravitational Wave Detection
eLISA is ESA's planned space-based gravitational wave observatory
Uses 3 spacecraft in triangular formation 50+ million km from Earth
Detects low-frequency gravitational waves using laser interferometry
Complements ground-based detectors like LIGO
What is eLISA
The evolved Laser Interferometer Space Antenna (eLISA) is the European Space Agency's ambitious project to detect gravitational waves from space. Unlike ground-based detectors that face Earth-based interference, eLISA operates in the vacuum of space to detect much lower frequency gravitational waves.
eLISA vs Ground-Based Detectors
Feature | eLISA (Space-Based) | LIGO (Ground-Based) |
|---|---|---|
Location | 50+ million km from Earth | Earth surface |
Frequency Range | Low frequency (0.1 mHz - 1 Hz) | High frequency (10 Hz - 1 kHz) |
Arm Length | 2.5 million km | 4 km |
Interference | Minimal (space vacuum) | Seismic, thermal, human activity |
Sources Detected | Massive black hole mergers, galactic binaries | Stellar black holes, neutron stars |
How eLISA Detects Gravitational Waves
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Formation Setup**
**3 spacecraft** form equilateral triangle with **2.5 million km** sides`"]
s2["`**Laser Measurement**
**Laser beams** continuously measure distances between **free-floating test masses**`"]
s3["`**Gravitational Wave Passage**
Wave **stretches and squeezes space** itself, changing distances minutely`"]
s4["`**Detection**
**Laser interferometry** detects tiny distance changes (smaller than atom's nucleus)`"]
s5["`**Data Analysis**
Computer algorithms identify gravitational wave signatures from noise`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5eLISA Configuration
Source: European Space Agency — ESA - LISA – measuring gravitational waves · www.esa.int
Question Context
This question tests knowledge of space-based scientific missions. The key association is eLISA = space-based + laser interferometer + gravitational wave detection. Options about neutrinos, missile defense, and solar flares use different technologies entirely.
Neutrino detection uses ice/water Cherenkov detectors (like IceCube), not laser interferometry
Missile defense systems use radar and infrared sensors, not space-based laser interferometers
Solar flare studies use X-ray and radio telescopes, not gravitational wave detectors
Don't confuse LIGO (ground-based, operational) with eLISA (space-based, planned)
Gravitational Waves Theory
Science And Technology gravitational waves
Gravitational Waves: Einstein's Prediction to Detection
Einstein predicted gravitational waves in 1916 via General Relativity
LIGO first detected them in 2015 - won 2017 Nobel Prize
Created by accelerating massive objects like merging black holes
Travel at speed of light and stretch/squeeze space itself
What Are Gravitational Waves
Gravitational waves are ripples in the fabric of space-time itself, predicted by Einstein's General Theory of Relativity in 1916. When massive objects accelerate - like two black holes spiraling into each other - they create waves that travel at light speed, stretching and compressing space as they pass.
Major Gravitational Wave Sources
Source Type | Frequency Range | Detector Type | Discovery Status |
|---|---|---|---|
Binary black holes | High (10-1000 Hz) | Ground (LIGO/Virgo) | First detected 2015 |
Neutron star mergers | High (10-1000 Hz) | Ground (LIGO/Virgo) | Detected 2017 |
Massive black hole mergers | Low (mHz) | Space (eLISA) | Target for future |
Galactic white dwarf binaries | Very low (μHz) | Space (eLISA) | Predicted millions |
Cosmic inflation | Ultra-low | Cosmic microwave background | Theoretical |
Gravitational Wave Timeline
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**1916 Prediction**
**Einstein** predicts gravitational waves in General Relativity`"]
s2["`**1970s-80s Evidence**
**Hulse-Taylor pulsar** shows orbital decay matching wave energy loss`"]
s3["`**2015 First Detection**
**LIGO detects** waves from black hole merger (**GW150914**)`"]
s4["`**2017 Nobel Prize**
**Physics Nobel** awarded to LIGO founders`"]
s5["`**Future Space Detection**
**eLISA** planned to detect low-frequency waves from space`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Gravitational waves ≠ gravity waves (atmospheric phenomenon in meteorology)
They stretch space itself, not just move objects through space
Einstein initially doubted his own prediction - thought they might not be real
LIGO detection came exactly 100 years after Einstein's prediction (1916→2015)
Laser Interferometry Detection Method
Science And Technology Laser Interferometer
Laser Interferometry: Detecting Tiny Space Distortions
Laser interferometry measures tiny changes in distance using light wave interference
Can detect changes smaller than 1/10,000th of a proton's width
Uses L-shaped arms with laser beams bouncing between mirrors
Identical technology in ground-based LIGO and space-based eLISA
How Interferometry Works
Laser interferometry splits a laser beam into two paths, sends them along perpendicular arms, and recombines them. When the arms have identical lengths, the beams interfere constructively (bright). When gravitational waves stretch one arm and compress the other, the path difference creates destructive interference (dark) - revealing the wave's passage.
Detection Process
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Laser Split**
**Single laser beam** split into two perpendicular paths`"]
s2["`**Arm Travel**
Beams travel down **L-shaped arms**, bounce off mirrors multiple times`"]
s3["`**Gravitational Wave**
Wave **stretches one arm, compresses other** by tiny amount`"]
s4["`**Path Difference**
Different arm lengths create **phase shift** between returning beams`"]
s5["`**Interference Pattern**
Recombined beams show **brightness changes** indicating wave passage`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Interferometer Sensitivity Comparison
Parameter | Ground-Based LIGO | Space-Based eLISA |
|---|---|---|
Arm Length | 4 km | 2.5 million km |
Sensitivity | 10^-21 meters | 10^-20 meters (lower freq) |
Frequency Range | 10 Hz - 1 kHz | 0.1 mHz - 1 Hz |
Main Noise Source | Seismic vibrations | Spacecraft positioning |
Detection Method | Suspended mirrors | Free-floating test masses |
Interferometry ≠ spectroscopy - measures distance changes, not light colors
The arms don't physically stretch - space itself between the mirrors expands/contracts
Sensitivity is relative - space detectors are less sensitive but detect different frequencies
Multiple bounces in LIGO arms increase effective length from 4km to ~1000km
Space Detection vs Alternative Methods
Science And Technology neutrinos missile defence system solar flares
Why Other Options Are Wrong: Different Detection Technologies
Neutrino detection uses water/ice Cherenkov detectors, not laser interferometry
Missile defense systems use radar and infrared, not space-based lasers
Solar flare studies use X-ray and radio telescopes, not gravitational wave detectors
Detection Methods Comparison
Phenomenon | Detection Method | Key Technology | Example Projects |
|---|---|---|---|
Gravitational Waves | Laser interferometry | Laser beams, mirrors | LIGO, eLISA |
Neutrinos | Cherenkov radiation | Water/ice tanks, photomultipliers | IceCube, Super-K |
Missile Defense | Radar + Infrared | Radio waves, heat sensors | THAAD, Patriot |
Solar Flares | X-ray/Radio telescopes | Electromagnetic spectrum | SDO, SOHO |
Why Each Wrong Option Fails
Neutrino detection (Option A): Neutrinos are nearly massless particles that barely interact with matter. Detectors like IceCube use huge volumes of ice/water to catch rare interactions that produce Cherenkov light flashes
Missile defense (Option C): Defense systems track incoming projectiles using ground-based radar and infrared sensors to detect heat signatures. No connection to space-based laser interferometry
Solar flares (Option D): Solar activity monitoring uses X-ray telescopes and radio antennas to detect electromagnetic radiation bursts. Studies plasma dynamics, not gravitational effects
Don't confuse particle detection (neutrinos) with wave detection (gravitational waves)
Military applications of lasers exist but eLISA is purely scientific research
Solar studies use many space telescopes but they detect electromagnetic radiation, not spacetime distortions