Ripples in the shape of space

Science · Astronomy & Astrophysics · ages 23-24

Name ______________________ Date ____________

Which motion makes gravitational waves?
- A planet circling steadily forever
- A star sitting perfectly still
- Two black holes spiraling together
What is a gravitational wave?
- A ripple at light speed
- A push of air between stars
- A steady gravitational pull
A smooth steady change in matter radiates gravitational waves.
Circle one: True False
Why is there no monopole or dipole gravitational radiation?
- Only quadrupole lumps radiate
- Gravity has no sources at all
- Waves travel too slowly to form
What does a passing wave do to a ring of free marbles?
- It pushes every marble forward together
- Flipping tall-thin and wide-flat ovals
- It freezes the marbles in place
Why is the measured strain so tiny?
- Weak coupling to matter
- Detectors are far too long
- Waves arrive far too often
Theo says the wave shoves marbles forward like an ocean wave. What is wrong?
- The merger was too far away
- Strain is too small to matter
- Sideways stretch and squeeze
How does LIGO sense a passing wave?
- Radio dishes hear the merger sound
- Lasers track mirror strain
- Thermometers track the wave heat

Answer key

For grown-ups. Fold this page away before handing over the rest.

Two black holes spiraling together · Lumpy unsymmetric acceleration radiates; steady setups stay silent.
A ripple at light speed · Moving matter readjusts geometry, and the change travels as a ripple.
False · Only lumpy unsymmetric acceleration radiates.
Only quadrupole lumps radiate · Symmetric overall motions cannot shake quadrupole geometry.
Flipping tall-thin and wide-flat ovals · Transverse stretch and squeeze alternate, never a forward shove.
Weak coupling to matter · Weak coupling means kilometer arms shift sub-proton widths.
Sideways stretch and squeeze · The action is sideways and alternating, never a forward push.
Lasers track mirror strain · Bouncing laser light tracks the minuscule arm change called strain.