Light vs Electricity — 3 Physics Reasons Why CPO Can't Save 13.4 J/token

13.4 J/token — Do You Know What That Means? Running an LLM on an RTX 4060: 145W power draw, 10.8 tokens/sec generation. Simple division gives 13.4 joules per token . 13.4J means a single AA battery's entire energy produces only 700 tokens. Two batteries for ~1000 characters of text. Of that 13.4J, how much actually goes to matrix multiplication? Under 5%. The rest is copper wire resistance heating inside the chip, bus driving energy for DRAM round-trips, and power supply losses. "Computation is almost free. Moving data is expensive." — That's the semiconductor reality of 2026. The root-cause fix everyone's betting on: optical interconnects , specifically CPO (Co-Packaged Optics) . Place optical devices right next to the compute chip, minimize electrical signal travel distance. NVIDIA and Intel are both investing heavily. But here's my position: CPO is palliative care, not a cure. This article covers three physical walls CPO cannot break, plus what technologies might actually matter — w