Has cosmic background radiation been measured underground?

[Simon B]

I am interested to know if cosmic microwave (160 Ghz) or cosmic radio (20-50 Mhz) background radiation has ever been measured/detected underground or underwater?

This may seem like an odd question as you’d expect lots of rock and water to attenuate or block the cosmic radiation photons, but I have come up with a (very implausible!) cosmological concept where they might still be detectable.

This isn’t quite as unlikely as it sounds; I have a sailboat with radar, radio and a compass. The ordinary photons that make the radio and radar work are blocked/reflected by rock and water, while the virtual photons that make the compass work (according to QED) pass quite happily through the Earth and oceans. Has anyone ever tried an experiment to see how cosmic background radiation photons behave?

 

[rootone]

CMB radiation is normal electomagnetism, there's nothing virtual or otherwise unusual about it.
It is also extremely faint and difficult to detect even before attempting to detect it through several meters of rock or water.
The best CMB data we now have required a series of sophisticated space telescopes to be seen in any detail.

 

[Simon B]

rootone, yes that’s what we understand cosmic background radiation to be, in which case you wouldn’t expect to be able to detect it underground or underwater. My question is has anyone ever done an experiment to verify this?

 

[glappkaeft]

Trying to detect the cosmic background radiation in particular, I doubt anyone competent has tried that. People running into problems with line of sight in the VHF band and up are probably in the millions or billions (walkie-talkies, FM radio, TV broadcast. etc).

 

[Ibix]

As rootone notes, the CMB is simply microwaves. There's nothing to detect underground.

You may wish to review the PF rules on personal theories (short version: not to be discussed here) and our Insights articles on virtual particles before posting further.

 

[PeterDonis]

the virtual photons that make the compass work (according to QED)

How do virtual photons make your compass work according to QED?

 

[kimbyd]

rootone, yes that’s what we understand cosmic background radiation to be, in which case you wouldn’t expect to be able to detect it underground or underwater. My question is has anyone ever done an experiment to verify this?

The frequencies of radiation for the CMB are mostly in the 30GHz-500GHz frequency range. We understand how this kind of radiation interacts with matter extremely well, in part because we use signals in this range for some wireless communications. There's not really any point to trying to measure it underground.

Most of the CMB radiation is blocked by the atmosphere anyway.

 

[Simon B]

glappkaeft; I suspect you’re right that nobody competent has tried to measure this (I can’t find any papers) but I posted the question to see if anyone else had heard of an experimental test.

ibix; I am not advancing or proposing a personal theory here, I am merely seeking information on experiments that might have been done in the past.

PeterDonis; I wouldn’t want this post to digress onto virtual photons, QED or how a compass works, interesting though all those subjects are!

kimbyd; I know we think we understand the CMB well, but I’m not sure the same can be said of the cosmic radio background (see Al Kogut’s introductory presentation at the July 2017 Radio Synchotron Background Workshop https://physics.richmond.edu/rsb-conference/program.html). You’ll see from the table in his paper that the cosmic background radio noise at 22 and 44 Mhz is very strong, and I’m not aware of a good, accepted explanation for this.

 

[PeterDonis]

I wouldn’t want this post to digress onto virtual photons, QED or how a compass works, interesting though all those subjects are!

Then you shouldn't have mentioned it in the OP of this thread. If it's off topic, it's off topic. But it's also mistaken, which is why I asked about it, since you mentioned it.

 

[kimbyd]

kimbyd; I know we think we understand the CMB well, but I’m not sure the same can be said of the cosmic radio background (see Al Kogut’s introductory presentation at the July 2017 Radio Synchotron Background Workshop https://physics.richmond.edu/rsb-conference/program.html). You’ll see from the table in his paper that the cosmic background radio noise at 22 and 44 Mhz is very strong, and I’m not aware of a good, accepted explanation for this.

The reason is very simple: the CMB itself is incredibly bright. Something like 99% of all of the light that has ever been emitted in the history of the universe is contained within the CMB. The frequency range I mentioned is the range where the CMB is brightest, but it's so bright that it still has significant contributions at both higher and lower frequencies.

At the frequencies where the CMB is brightest (around 150GHz or so), it's so incredibly bright that small temperature variations (about 1/100,000th the size of the average temperature) are themselves brighter than anything else in the sky across most of the sky.

The CMB itself is also almost a perfect black body. The COBE satellite, which provided the first accurate estimate of the CMB spectrum, is plotted with its error bars exaggerated by a factor of 400:
https://www.researchgate.net/figure/CMB-spectrum-measured-by-COBE-the-error-bars-are-exaggerated-by-a-factor-of-400-ref_fig2_235909795

The CMB is one of the cleanest, simplest, and best-understood astrophysical signals in existence.

 

[Chronos]

The number of CMB photons is truly astounding, but, so is their weakness. It's just the price inherent to being a 3K black body emission. The number of these photons energetic enough to penetrate just about anything [air, water, earth, etc.] is all but zero. They are the evil anti-twins of neutrinos, which can penetrate pretty much anything. but interact about as often as a spayed nun in a strip club..

 

[kimbyd]

The number of CMB photons is truly astounding, but, so is their weakness. It's just the price inherent to being a 3K black body emission. The number of these photons energetic enough to penetrate just about anything [air, water, earth, etc.] is all but zero. They are the evil anti-twins of neutrinos, which can penetrate pretty much anything. but interact about as often as a spayed nun in a strip club..

At these frequencies, the low individual energies of the photons isn't the important factor. Even lower-energy radiation can sometimes penetrate some materials more readily. Rather, it's how they interact with the specific matter that makes up various materials. This is controlled by whether or not the photons couple to certain changes in energy of the materials. I don't remember the exact details, but I think the photons at these energies couple to changes in the rotational energy of the molecules in the atmosphere.

In this particular case, the carbon dioxide and water vapor in the atmosphere tend to interact pretty strongly with radiation in the CMB range. This is why ground-based CMB experiments seek out locations with high altitudes (so that the air is thinner) and dry air (so that the water vapor doesn't absorb as much of the radiation). They also explicitly select frequency bands to measure which interact with the atmospheric molecules less.

With respect to solids or liquids, such materials tend to have many more ways that low-energy photons can interact with them, and so block those materials pretty efficiently. Though it depends quite a lot upon the specific materials and the frequency of the radiation. Either way, nothing is really learned by measuring the CMB through all of this stuff. All that you get out of it is an understanding of how well those materials block radiation in the measured range, which can be measured far more easily, cheaply, and precisely in lab experiments where you use an antenna to create a source of radiation in the given frequency and then block it with the material in question.

 

[Vanadium 50]

My question is has anyone ever done an experiment to verify this?

People don't build radio telescopes underground for the same reason they don't build optical telescopes underground.

 

[Jean Tate]

I am interested to know if cosmic microwave (160 Ghz) or cosmic radio (20-50 Mhz) background radiation has ever been measured/detected underground or underwater?

As rootone notes, the CMB is simply microwaves. There's nothing to detect underground.

"cosmic radio (20-50 MHz)" is, likewise, simply radio.

So the OP's question can be re-phrased, without any significant loss of meaning, as "has 20-50 MHz radio ever been measured/detected underground or underwater?"

Which is, it seems to me, a good question for an entirely different part of PF. Perhaps you could re-ask your question elsewhere, Simon B? And, rather than a simple, narrow Yes/No question, maybe you could ask about what's known - via empirical observations - about the propagation of electromagnetic radiation, of frequencies from ~10 MHz to ~200 GHz, in rock/sand/etc and water?

I'm almost tempted to ask an OT question: in which parts of the universe "today" is the CMB undetectable? One part of the answer is "in the Sun, and all other stars" ... maybe there are parts of the ISM that are so dense (electron density) that the CMB can't get in? Also, in future, when the CMB has moved to ~20 MHz frequencies (say), will it be undetectable throughout parts of some galaxies? Etc.