5 ms·

So you've got a bunch of responses, but as a guy with a Master's in applied physics I wanted to chime in with a bit more of a long explanation. The word "radia

by drostie 12y ago

So you've got a bunch of responses, but as a guy with a Master's in applied physics I wanted to chime in with a bit more of a long explanation. The word "radiation" just means that something radiates -- it travels off to infinity. In this case we're talking about electromagnetic radiation, which spans a vast continuum from radio waves through microwaves to infrared and red, across the visible spectrum to deep blue, then on into ultraviolet, X-ray, and gamma light. It turns out that this radiation is quantized -- meaning it comes in lumps of a certain energy E = hf where h is a fundamental constant and f is the frequency of the light (equivalently, f = c / L where L is the wavelength). Light also comes with a certain "kick" or momentum p = E / c. We knew the latter formula from classical electromagnetism but the former formula was awarded two Nobel prizes, one to Max Planck and one three years later to Albert Einstein. It is presently thought that the blue side of the non-visible electromagnetic radiation spectrum (UV, X-rays, Gamma rays) is cancer-causing, while the visible and red-side of nonvisible is not. This comports with the Planck/Einstein law for the energy of the photons, which approaches the bond energies for several common atomic bonds in the visible spectrum and exceeds it as we go into the ultraviolet. (We essentially see light by having the light excite these bonds, but not so much that it tears them apart, so as they "relax" to their starting configuration they release the energy and activate neurons.) Microwaves are about 1mm or 1cm long, on the red side. They are emitted by microwave ovens, cell phones, wifi hotspots, and millimeter-wave detectors. Right now it's not thought that these are "dangerous" radiation any more than white light is, because their "kicks" don't excite the atomic bonds but are instead absorbed by proteins as a whole, in a process we presently think is indistinguishable from any other sort of heat transfer. That is, they heat you up, but don't do much else. If they did something else, probably very large changes would have to be made to our modern scientific understanding, which I of course would totally support if experiments bore it out. At present there are no good experiments which show any other effects of microwaves on biological tissue, other than the heating thing.

thinkling 12y ago
I like this response a lot and am going to adapt it to explain this to my radiation-paranoid family. The concept of wavelength as the sole distinction between these types of radiation is probably abstract to most non-science-educated people. Can you (or anyone else) think of a good concrete real-world analogy of different types of X that vary only in Y and some X are harmless but those with Y are not? Maybe an analogy of throwing sand at someone vs. shooting a bullet?
- jessaustin 12y ago
  Maybe you could relate it to temperature? A simple quantity, but intuitively safe at some magnitudes and dangerous at others.
- brianpan 12y ago
  Ocean waves crashing against a retaining wall. It doesn't matter how many small waves come, it's only waves greater than a certain height that are dangerous.
- drostie 12y ago
  The sand/bullet one is probably apt, if indirect. The issue is that different "kicks" get absorbed in different ways by the stuff which makes up your cells. One gets absorbed by the chemical bonds and tears them apart; one gets absorbed by the molecule as a whole. I think maybe the best way to give the idea is to contrast a car crash with a bullet at the same energy. According to Wikipedia, a really strong rifle cartridge (in this case, the .220 Swift) fires its bullet with at most 2.4 kJ of kinetic energy, which is about the energy of me moving at 15 mph. So you can imagine me, getting shot, flying backward at ~10 mph. But also there's the exact same energy and momentum transfer as is in me falling asleep and veering into a tree while driving at 10 mph. So why do I think that the 10mph crash is survivable as long as I don't get thrown from the vehicle, while the bullet would likely be fatal? The difference is that the seat belt distributes the force over most of my upper torso, whereas the rifle distributes all of its kick in a particular place. Similarly, the "smaller" photons distribute all of their kick on particular atoms, while the "bigger" photons tend to distribute their kick on the protein as a whole. One "rips the stuff apart", the other causes it to bump into its surroundings more.
  - thinkling 12y ago
    Thanks. What's your take on the possibility of damage suffered from exposure to RF radiation? There are reports from credible institutions (/u/jamoes mentions one above) that RFR, despite causing "only heating", may have detrimental impacts. When I see lists of studies like this [1], it's hard to know what to think. Are most of these weak studies or unsettled science? I know this is a really broad question; I'm obviously not asking for comments on specific studies listed those tables. I'm curious about comments on the seeming contradiction between the observation that at a theoretical level RF radiation at moderate intensity is thought to be known to be provably harmless, and the large number of reports of observed non-trivial(?) effects. [1] http://www.bioinitiative.org/rf-color-charts/ http://www.bioinitiative.org/rf-color-charts/
thinkling 12y ago
PS: so in electromagnetic radiation, shorter wavelengths carry more energy, whereas in sound, longer wavelengths (bass) carry more energy. (Right?) I'm not physics-savvy enough why these effects are opposite; is there an explanation for this?
- jessaustin 12y ago
  Sound energy is unrelated to audio frequency. Intuitively, it's possible to have quiet, deep sounds and loud, high-pitched sounds.
  - schoen 12y ago
    I think you're right (audio frequency doesn't appear in the formulas I found for sound energy), but I don't think the analogy fully demonstrates why, since it's also possible to have bright or dim light of a particular color! The issue about the energy of electromagnetic radiation depending on frequency is, if I understand correctly, a quantum issue. https://en.wikipedia.org/wiki/Photoelectric_effect https://en.wikipedia.org/wiki/Photoelectric_effect That is, quantum theory explains why there is such a thing as nonionizing electromagnetic radiation.
  - jwmerrill 12y ago
    It's also possible to have faint blue light, and bright red light. Sound energy is quantized too, but for audible frequencies, hf is small compared to kT, so quantum effects are swamped by thermal effects.
- pdonis 12y ago
  "More energy" can mean two different things. In the case of sound, only one of those meanings--the amplitude of the wave--is relevant: soft sounds have lower amplitude and loud sounds have higher amplitude. The frequency of the wave, as jessaustin pointed out, is independent of how soft or loud it is, and for sound, there isn't any useful sense in which any frequency carries "more energy" than any other frequency, given that the amplitudes are the same. With regard to light, however, there is a second possible meaning for "more energy": not a higher amplitude of the classical wave, but more energy contained in a single quantum of the light (i.e., a single photon). Light of higher frequency (toward the blue/ultraviolet end of the spectrum) has more energy per quantum; light of lower frequency (toward the red/infrared/microwave end of the spectrum) has less. This sense of "more energy" is still independent of wave amplitude: wave amplitude corresponds to number of photons (more precisely, the number of photons is proportional to the amplitude squared). So you can have faint light (few photons) of high frequency (more energy per photon); or you can have bright light (lots of photons) of low frequency (less energy per photon). The total energy contained in the light depends on both of these factors; but the total energy in the light is not the crucial factor involved (see below). It turns out that, when you are looking at the possible effects of radiation on the body, the energy per photon is the most important factor, because that is what determines what kind of interactions the radiation can have with the molecules that make up your body. UV, X-rays, and gamma rays have enough energy per photon to break apart the chemical bonds that hold together things like proteins in your cells; that's what makes them potentially cancer-causing. Microwaves, OTOH, don't have enough energy per photon to break chemical bonds; all they can do is make the molecules, like proteins, vibrate more rapidly, which just means heating them up.
jamoes 12y ago
Thanks for the reply. I don't know if wikipedia is the best source, but talking about health risks, it states: > A team led by Los Alamos National Labs found that although the forces that terahertz waves exert on double-stranded DNA are tiny, in certain circumstances resonant effects can unzip the DNA strands, tearing them apart. This creates bubbles in the strands that can significantly interfere with processes such as gene expression and DNA replication. [1] Unzipping DNA strands in certain circumstances sounds pretty harmful. I understand theoretically why millimeter waves are lower risk than backscatter x-rays, but it seems to me that there still are risks. In my opinion, before sending the population through these things, we need studies of their long-term effects from real-world exposure, not just theoretical reasoning about why the rays are most likely safe. [1] https://en.wikipedia.org/wiki/Millimeter_wave_scanner#Possible_health_effects https://en.wikipedia.org/wiki/Millimeter_wave_scanner#Possib...

by drostie 12y ago

thinkling 12y ago

I like this response a lot and am going to adapt it to explain this to my radiation-paranoid family. The concept of wavelength as the sole distinction between these types of radiation is probably abstract to most non-science-educated people. Can you (or anyone else) think of a good concrete real-world analogy of different types of X that vary only in Y and some X are harmless but those with Y are not? Maybe an analogy of throwing sand at someone vs. shooting a bullet?

jessaustin 12y ago
Maybe you could relate it to temperature? A simple quantity, but intuitively safe at some magnitudes and dangerous at others.
brianpan 12y ago
Ocean waves crashing against a retaining wall. It doesn't matter how many small waves come, it's only waves greater than a certain height that are dangerous.
drostie 12y ago
The sand/bullet one is probably apt, if indirect. The issue is that different "kicks" get absorbed in different ways by the stuff which makes up your cells. One gets absorbed by the chemical bonds and tears them apart; one gets absorbed by the molecule as a whole. I think maybe the best way to give the idea is to contrast a car crash with a bullet at the same energy. According to Wikipedia, a really strong rifle cartridge (in this case, the .220 Swift) fires its bullet with at most 2.4 kJ of kinetic energy, which is about the energy of me moving at 15 mph. So you can imagine me, getting shot, flying backward at ~10 mph. But also there's the exact same energy and momentum transfer as is in me falling asleep and veering into a tree while driving at 10 mph. So why do I think that the 10mph crash is survivable as long as I don't get thrown from the vehicle, while the bullet would likely be fatal? The difference is that the seat belt distributes the force over most of my upper torso, whereas the rifle distributes all of its kick in a particular place. Similarly, the "smaller" photons distribute all of their kick on particular atoms, while the "bigger" photons tend to distribute their kick on the protein as a whole. One "rips the stuff apart", the other causes it to bump into its surroundings more.
- thinkling 12y ago
  Thanks. What's your take on the possibility of damage suffered from exposure to RF radiation? There are reports from credible institutions (/u/jamoes mentions one above) that RFR, despite causing "only heating", may have detrimental impacts. When I see lists of studies like this [1], it's hard to know what to think. Are most of these weak studies or unsettled science? I know this is a really broad question; I'm obviously not asking for comments on specific studies listed those tables. I'm curious about comments on the seeming contradiction between the observation that at a theoretical level RF radiation at moderate intensity is thought to be known to be provably harmless, and the large number of reports of observed non-trivial(?) effects. [1] http://www.bioinitiative.org/rf-color-charts/ http://www.bioinitiative.org/rf-color-charts/

thinkling 12y ago

PS: so in electromagnetic radiation, shorter wavelengths carry more energy, whereas in sound, longer wavelengths (bass) carry more energy. (Right?) I'm not physics-savvy enough why these effects are opposite; is there an explanation for this?

jessaustin 12y ago
Sound energy is unrelated to audio frequency. Intuitively, it's possible to have quiet, deep sounds and loud, high-pitched sounds.
- schoen 12y ago
  I think you're right (audio frequency doesn't appear in the formulas I found for sound energy), but I don't think the analogy fully demonstrates why, since it's also possible to have bright or dim light of a particular color! The issue about the energy of electromagnetic radiation depending on frequency is, if I understand correctly, a quantum issue. https://en.wikipedia.org/wiki/Photoelectric_effect https://en.wikipedia.org/wiki/Photoelectric_effect That is, quantum theory explains why there is such a thing as nonionizing electromagnetic radiation.
- jwmerrill 12y ago
  It's also possible to have faint blue light, and bright red light. Sound energy is quantized too, but for audible frequencies, hf is small compared to kT, so quantum effects are swamped by thermal effects.
pdonis 12y ago
"More energy" can mean two different things. In the case of sound, only one of those meanings--the amplitude of the wave--is relevant: soft sounds have lower amplitude and loud sounds have higher amplitude. The frequency of the wave, as jessaustin pointed out, is independent of how soft or loud it is, and for sound, there isn't any useful sense in which any frequency carries "more energy" than any other frequency, given that the amplitudes are the same. With regard to light, however, there is a second possible meaning for "more energy": not a higher amplitude of the classical wave, but more energy contained in a single quantum of the light (i.e., a single photon). Light of higher frequency (toward the blue/ultraviolet end of the spectrum) has more energy per quantum; light of lower frequency (toward the red/infrared/microwave end of the spectrum) has less. This sense of "more energy" is still independent of wave amplitude: wave amplitude corresponds to number of photons (more precisely, the number of photons is proportional to the amplitude squared). So you can have faint light (few photons) of high frequency (more energy per photon); or you can have bright light (lots of photons) of low frequency (less energy per photon). The total energy contained in the light depends on both of these factors; but the total energy in the light is not the crucial factor involved (see below). It turns out that, when you are looking at the possible effects of radiation on the body, the energy per photon is the most important factor, because that is what determines what kind of interactions the radiation can have with the molecules that make up your body. UV, X-rays, and gamma rays have enough energy per photon to break apart the chemical bonds that hold together things like proteins in your cells; that's what makes them potentially cancer-causing. Microwaves, OTOH, don't have enough energy per photon to break chemical bonds; all they can do is make the molecules, like proteins, vibrate more rapidly, which just means heating them up.

jamoes 12y ago

Thanks for the reply. I don't know if wikipedia is the best source, but talking about health risks, it states: > A team led by Los Alamos National Labs found that although the forces that terahertz waves exert on double-stranded DNA are tiny, in certain circumstances resonant effects can unzip the DNA strands, tearing them apart. This creates bubbles in the strands that can significantly interfere with processes such as gene expression and DNA replication. [1] Unzipping DNA strands in certain circumstances sounds pretty harmful. I understand theoretically why millimeter waves are lower risk than backscatter x-rays, but it seems to me that there still are risks. In my opinion, before sending the population through these things, we need studies of their long-term effects from real-world exposure, not just theoretical reasoning about why the rays are most likely safe. [1] https://en.wikipedia.org/wiki/Millimeter_wave_scanner#Possible_health_effects https://en.wikipedia.org/wiki/Millimeter_wave_scanner#Possib...