Doesn’t all radar travel at light speed by definition? Because it’s radio waves? Which travel at light speed?
this post was submitted on 02 Dec 2024
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this article has a better explanation
https://interestingengineering.com/military/submarine-detection-at-light-speed-china
ELF signals, with wavelengths longer than 100 meters (328 feet), typically require large distances between antenna units. Traditionally, generating low-frequency signals needed massive antennas, like the ELF facility in central China, which has antennas over 100 km (62 miles) long.
In contrast, Li’s team has reduced the length of the emitting array to just about 100 meters (328 feet), making it possible to easily install these antennas on Chinese naval ships. The high-frequency, high-power electromagnetic waves emitted by these antennas converge in the sky to create a virtual radio-emitting source. As one source dissipates, another is instantly generated, ensuring a continuous flow of low-frequency signals.
as @D61@hexbear.net pointed out, the virtual source is what's moving at near the speed of light. the virtual source is the sky. the actual source is on a ship. it sounds like they're generating an interference pattern and reflecting that off the atmosphere to produce extremely low frequency electromagnetic waves capable of penetrating the water column. it's the group velocity of the wave packet that's moving at close to the speed of light, or something like that.
I was about to post the same thing ;)
Slightly poorly written article title.
Researchers in China have harnessed the power of the Doppler effect to achieve a breakthrough in submarine detection
According to the researchers, this virtual signal source is capable of emitting electromagnetic waves continuously while travelling at close to the speed of light.
The thing moving at the speed of light is the emitting source.
That makes more sense. The concept is pretty cool, and difficult to explain. My first thought was that the article was written by someone who wasn't very scientifically literate, but the author does actually seem to have the background to understand this stuff.
actually, light speed c is only achieved in a vacuum...
No I had the same thought lol I was like what kind of shitty budget radar waves DON'T operate at light speed?
Light speed is light speed, and c is c. They coincide in a vacuum. Light always travels at light speed.
Thesis: waves
Antithesis: particles
Synthesis: some nerd stuff I dunno
Light speed is light speed, and c is c. They coincide in a vacuum. Light always travels at light speed.
It's a little more complicated than that. Like, yes light is always traveling at c. But as it moves through a medium, it interacts with that medium. It gets refracted, absorbed, re-emitted, diffracted, etc: All things that add time to the photons' travels, lowering its observed velocity.
That is essentially what I was saying. The observed effect of light (the group velocity of light) travels at the speed of light. That is essentially to say, for everyday purposes like transmission of signals, the speed of light is the (observed) speed of light. In a vacuum, this is c, but in other media, the speed of light is slower than c, so c might be better referred to as the speed of causality.
Edit: I will mention that some peg c to the speed of light in any medium, and refer to the speed of light in a vacuum as c₀. This usage is endorsed in official SI literature.
Ya I was just being a goof lol. Interesting about c vs c~0~ tho, never seen that usage before
what kind of shitty budget radar waves DON'T operate at light speed?
shooting rubber balls in random directions and seeing if they bounce off something
The US military uses this system, but this is just so they can get away with throwing rubber balls at high speeds without it being an act of war