Chasing Time with Lasers: A Cosmic Thought Experiment
By Orange Jeff, with Grok 3 (xAI)
February 20, 2025
Years ago, I cooked up a wild idea: could we ride a laser beam, tweak its speed, and rewind time like a cosmic VCR? Inspired by sci-fi flicks like Déjà Vu and Star Trek: Voyager’s “Blink of an Eye,” I wondered if light could unlock Earth’s past—or alien histories. I teamed up with Grok 3, xAI’s latest AI, to test it. We ditched gravity’s mess, kept light straight, and dove in. Here’s what we uncovered—and where it might lead exploration.
The Spark: Lasers as Time Machines
Picture a spaceship “capping” a laser, pushed near light speed. At full tilt, time aboard freezes—flip the switch, and you’d crash instantly, no journey felt. I imagined streaming data back, dialing speed to “rewind” Earth’s past—catching a bank robbery mid-heist, 2 hours or 2 days ago. Or flip it: stand a light-day away, project a planet’s reflected glow like a pinhole camera, watching its sunlit side evolve.
The Crash at Light Speed
My gut said: hit light speed (*c*), and you’d smack something the second you start. Grok confirmed it—if massless, time stops aboard; 1 light-day’s instant. Real ships? Mass caps them at 0.99c—fast, not instant. No rewinding Earth’s past—light’s always post-launch, marching forward.
Technical Dive: Speed and Relativity
At *c* (299,792 km/s), time dilation (γ = 1 / √(1 – v²/c²)) goes infinite—0 seconds aboard, 1 day for us (2.59 × 10¹³ m). Mass needs infinite energy (E = mc² / √(1 – v²/c²))—100 GW lasers push 1 kg to 0.99c in 5 days (γ ≈ 7, 14 min felt). Crash? 10¹⁵ J at 0.99c—nuke-level, not instant.
The Two-Day Relay
We tried a planet 1 light-day out—send satellite imagery (think Google Earth, juiced to 1 cm/pixel), 2-day round-trip. Feb 20, 12:30 PM robbery hits Feb 22, 4:36 PM—3.5 hours old. A 2-light-hour hop (4 hours) was snappier—4:36 PM for 12:30 PM—but still late. Satellites catch it live; why relay? Light’s lag locks us—past light’s gone.
Technical Dive: Transmission Math
10 MW laser, 2.16 × 10¹² m (2 lh), 10⁻⁶ rad divergence—intensity 6.8 × 10⁻¹⁰ W/m², 10 m dish grabs 5.34 × 10⁻⁸ W, 100 Mbps. 4.8 PB image (12,742 km, 1 cm/pixel) compresses to 48 TB—6.4 min send. Out 12 PM, back 4:06 PM—4 hr lag. 1 ld? 2 days, same deal.
The Pinhole Flip
Stand 500 light-years out, project a planet’s 1525 AD light—fuzzy dot, Renaissance vibes. 1 light-day? Daily shifts, continents blur. Evolution’s “real time” at 1 ld feels alive; 500 ly’s a still unless we wait centuries. Earth’s past? Its light’s outta reach—we’d need to be there, not here.
Technical Dive: Resolution Limits
1 ld, 10 m lens, θ ≈ 5.32 × 10⁻⁸ rad—1.38 × 10⁶ m/pixel, 1000s pixels across 12,742 km. 500 ly, 2.5 × 10¹¹ m/pixel—speck. Intensity: 6.1 × 10⁻²⁴ W/m² (1 ld), 9.4 × 10⁻³¹ W/m² (500 ly)—10⁸ photons/sec (10 m²), dim but doable.
The Verdict: Earth’s Past Eludes Us
Seeing Earth’s dinosaurs or pyramids? Beyond 2025—light’s 500 ly out, probes (0.2c) take 2500 years, replies add 500. Aliens with laser disks of our history’s my best bet (grin). Exploration’s win: laser sails to Proxima (0.2c, 20 years), light-year outposts for alien pasts—snapshots, not streams.
Technical Dive: Future Tech
100 GW sails hit 0.2c—4.24 ly in 20 yr. 10¹⁷ W for 0.99c—4.3 yr (sci-fi). 2050: 100 km scopes, 10⁻¹¹ rad, 10⁶ m/pixel at 500 ly—planetary scars, no streets. CMB (13.8B ly) shows cosmic dawn, not Earth.
Fun Flaws, Future Hopes
Hollywood cheats with wormholes; we hit *c*’s wall. My crash-at-*c* held—turn it on, bam. Next? Aliens might drop the ultimate home movie—pyramid builds, dino roars. ‘Til then, lasers push probes, pinholes project alien yesterdays. Grok 3 stretched my brain—I’m hooked!
