# What would it take to view "the whole EM spectrum"?

I know the EM spectrum goes off both ends, but nearly everything anyone has bothered to use it for has wavelengths between $$10^8$$m (ELF) and $$10^{-12}$$m or so (gamma rays). So for the purposes of this question lets just assume those 20 orders of magnitude represent everything of interest.

So then the question: how much hardware would it take to be able to observe all of that? Say if you are building a space probe? Would it be reasonable to assume that the average sensor could handle an order of magnitude window in that spectrum? More then that? Less than that?

• A space probe to detect $10^8$ meter radiation? I don't think that's remotely possible. Aug 15 at 19:43
• @DavidHammen: IIRC an antenna can be significantly smaller than a wavelength, (AM radios use between $10^2$ and $10^3$ shorter.) Assuming 30 Gage aluminum wire, that's just short of 40 tons, or about twice what a Falcon Heavy can send to mars. Expensive and by no means simple, but within the possible. -- OTOH: would those same wires work for $10^5$m? $10^4$m?
– BCS
Aug 15 at 22:07
• @DavidHammen Submarines can receive messages sent to them in the ELF range (due to it's strong ability to penetrate water). I can't imagine most submarines are $10^8\ m$ in size. Aug 17 at 21:21
• @zephyr Different organizations have different definitions of what ELF means. To the US Navy, 76 Hz qualified as extremely low frequency, which was what was used in Project ELF. That's a wavelength of about 4000 km. A receiving antenna doesn't have to be as long as the wavelength. An antenna several kilometers long will do. Russia uses 82 Hz, so an even shorter wavelength of 3700 km. Aug 18 at 1:54
• @BCS Besides the sheer impossibility of detecting 3 Hz ($10^8$ meter) radiation, why? The low frequency region that is attainable by spacecraft and offers useful science is the 100 kHz to 20 MHz range. This frequency range is unavailable to Earth-bound observatories because of the ionosphere, but could give us insights into the early universe (the interval between the CMBR and the first galaxies). Aug 18 at 2:07