Electrostatic state selector and telephone: what they have in common

1. Step 1. Electrostatic state selector — is part of — Maser. It selects the excited molecules.
2. Step 2. Maser — evolved into — Laser. A laser is an optical maser.
3. Step 3. Laser — is used in — LIGO. A laser.
4. Step 4. LIGO — has part — Photodiode. A photodetector of the interference.
5. Step 5. Photodiode — is used in — Fax. Scanning with a photocell.
6. Step 6. Fax — uses — Telephone. Transmission over a telephone line.

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