← INDEX — FIG. 00 — GW150914, 14 SEPTEMBER 2015, 09:50:45 UTC h = 1.0 × 10⁻²¹

RIPPLE
GRAVITATIONAL WAVES: LIGO, VIRGO, KAGRA & LISA

Two black holes merged, and for a fifth of a second space stretched by one part in 10²¹.

BEGIN — CHAPTER 01 →

CH.01 / 09 — WHAT A GRAVITATIONAL WAVE IS

Space that stretches one way and squeezes the other

Einstein 1916: waves of strain at the speed of light.

h = 1.0 × 10⁻²¹, ±0.002 fm per arm.

ARM-LENGTH CHANGE FROM A STRAIN

ΔL = δL_x − δL_y = h · L · δL_x = −δL_y ≈ h · L / 2

Best case: wave from overhead, polarised along the arms.

STRAIN h (LOG SCALE)—

Deformation exaggerated about 10²⁰ times.

CH.02 / 09 — FROM BARS TO LASERS

Fifty years of building an ear for spacetime

Weber's bars, then interferometers.

20 W → 700 W → 100 kW; Nobel 2017.

ADVANCED LIGO IN NUMBERS [1]

2 sites · 4 km arms · 1064 nm laser · 20 W → 700 W → 100 kW · isolation above 10 Hz · best at 100–300 Hz

Two sites, so that local noise is rejected.

CH.03 / 09 — GW150914

A fifth of a second that weighed two black holes

GW150914: 35 → 250 Hz, 0.2 s, SNR 24.

Chirp mass ≈ 30 M☉; 36 + 29 → 62.

CHIRP MASS AND TIME TO MERGER (LEADING ORDER) [1][9]

𝓜 = (m₁m₂)^3/5/(m₁+m₂)^1/5 = (c³/G)·[(5/96)·π^−8/3·f^−11/3·ḟ]^3/5 · t_c − t = (5/256)·(G𝓜/c³)^−5/3·(πf)^−8/3

Leading-order inspiral only.

CHIRP MASS 𝓜—

START FREQUENCY—

Presets and sound.

CH.04 / 09 — THREE SUNS OF ENERGY

Three suns turned into ripples, and nothing to see

3.0 M☉ radiated; peak 3.6 × 10⁴⁹ W.

E = mc² with the Sun's figures.

GW150914'S ENERGY, COMPUTED FROM [1] AND [11]

—

Sun's lifetime: 10 billion years at today's luminosity (round figure).

CH.05 / 09 — PSR B1913+16

The evidence that came decades early

Hulse & Taylor, 1974; Nobel 1993.

Observed/GR = 0.9983 ± 0.0016.

ORBITAL DECAY BY GRAVITATIONAL WAVES (PETERS–MATHEWS) [13]

Ṗ_b = −(192π/5)·(2πT☉/P_b)^5/3·f(e)·m_pm_c/(m_p+m_c)^1/3 · f(e) = (1 + 73e²/24 + 37e⁴/96)/(1 − e²)^7/2

T☉ = 4.9255 µs.

ECCENTRICITY e—

YEAR—

GR prediction from the published masses and orbit.

CH.06 / 09 — ARM LENGTH SETS THE BAND

Heavier pairs sing lower

f ≈ 4.4 kHz × (M☉/M).

LISA: 0.1 mHz – 0.1 Hz; PTAs: nanohertz.

TOTAL MASS (LOG SCALE)—

Bands are approximate.

CH.07 / 09 — GW170817 AND THE NETWORK TODAY

Heard, then seen 1.7 seconds later

GW170817: GRB 1.74 s later; NGC 4993.

Status, October 2026.

HOW FAST IS GRAVITY? [10][16]

—

Published bound and scale.

Status as of 11 October 2026.

CH.08 / 09 — LEGACY

A century from prediction to a new sense

Every telescope before 2015 caught light.

CH.09 / 09 — REFERENCES

RIPPLEGRAVITATIONAL WAVES: LIGO, VIRGO, KAGRA & LISA