This is extremely strange. Shouldn't this be impossible by the second law of thermodynamics?
Receiving more energy when a resistor in thermal equilibrium is connected to an antenna seemingly implies that energy gets transferred from an antenna with a resistor to a an antenna without a resistor, even at thermal equilibrium.
Maybe we'll later find it's an experimental subtlety, like the faster than light neutrinos.
I'm not sure, as this paper is very confusing in its style, but I think they try to modulate the load resistance connected to an antenna on the TX side. Since the open has a large real resistance (25k in their case), it's poorly impedance matched to the antenna and most of the noise powwr cannot be transferred to the antenna at 1.4 GHz they are using. 50 ohm load is well matched, hence the max noise power transfer to the antenna. This is all at TX.
I don't see a thermodynamic problem here. Noise modulation with switching is well known in electronics. Switched resistors and their noise is already analyzed. It is often in the context of noise parr of SNR though. They are using this noise modulation to transmit signals, which isn't too novel. I guess the transmit power is very low but this would be horrible for Shannon spectral efficiency because of the need for noise power detection, which cannot be instantenous.
I suspect GP's question is answered by the fact the system is not in thermal equilibrium. The view the antenna has is approx half of the sky whose temperature is far lower than room temp. Even indoors, the roof of your house is sufficiently transparent in RF that you are still seeing the sky behind.
If the same experiment was done in metal box with everything of constant temperature, I don't think it would be possible to transmit any bits.
AI will explain it, but it's against HN rules for me to post the explanation.
Basically they are misleading when they say "thermal equilibrium", same physical temperature does not imply thermal equilibrium.
FWIW, the "Significance" blurb at the very top says as much:
> An interesting feature of the system is that all components of the system are at the same physical temperature, but it functions because they have different noise temperatures.
(I assume it's not AI-generated.)
But it should. If you can get energy to flow one way between things at the same physical temperature that seems to violate thermodynamics and allow for perpetual motion.
I'll pretend you don't mean "sustained" to allow me to type something. Does this qualify?
Put a bowl of water down at room temperature, wait for one molecule to "evaporate", and I think you did it? Unfortunately they are now no longer at the same temperature.
Temperature is an average. You can still take advantage of the fact that there will be much lower and higher temperatures present. Also, what about Peltier effect? Same temperature when it starts.
Yes. If you try to design any device to capture all the molecules like that and extract their energy, you'll find that just as often your device dislodges a water molecule the other way, back into the pool and losing energy. Thus although You aren't the first to invent the Brownian ratchet.
The device shown in the OP appears to allow for a sustained thermally-driven energy transfer one way or the other depending on the bit value ou are sending.
only for passive systems.
what's described in this paper is not passive, it has a powered amplifier in there which lowers the "noise temperature"
same way a heat pump can move heat between things at the same temperature - inside and outside of house when you start it
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Now consider the alignments of red blood cells.
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