Question: My understanding is that radio telescopes can see farther than optical telescopes. That seems counter-intuitive since light travels much faster than sound. What am I missing here? — SS, New River, AZ
Answer: Both radio waves and light are electromagnetic in nature. Some man-made radio waves are encoded to carry information that can be converted into audio (like your favorite commercial radio stations or audio communication links). And some carry info that can be decoded into video. But they’re all still electromagnetic waves. The speed of sound has absolutely nothing to do with this.
It’s a common misconception though — that what you hear on radio is being transmitted as sound waves. However, sounds waves are compressional (aka “longitudinal”) and require a physical medium to propagate. Electromagnetic waves are transverse and require no medium … that’s why we can talk to astronauts on the ISS.
So the reason radio waves travel farther than light waves (in general) is because all the dust and gas out in space attenuates visible light, but is transparent to certain frequencies of radio waves. That’s how COBE could see nearly all the way back to the beginning of the Universe. The image at top ...