# What's the longest wavelength possible?

by Chaos' lil bro Order
Tags: longest, wavelength
 P: 683 1) If radio waves have wavelengths around 100 meters long and a frequency of about 10*7 Hz, are there any wavelengths in the EM Spectrum that are longer? 2) I've heard the Gravity Probe LISA is using interferometers spaced 5 million km apart to measure gravity, does this mean gravity waves are supposed to be about 5 million km long? If so why? 3) Also, if Wavelength = 300,000km/s / frequency and frequency = 1, then that means the Wavelength is 300,000km for f=1. So then, how could a gravity wave be longer than light speed's frequency of 1? Did space's expansion stretch the 300,000km into 5 million km? Please help me, I'd really like to know, thanks.
 P: 23 1) Theres no theoretical upper limit on the wavelenght of the EM-spectrum. On the horizon of our visible universe theres an barrier of "infinite redshift". Also, EM-radiation radiated by a body falling into a black hole will also redshift into "infinity" at the event horizon. 2) No, the 5 million km is because gravity waves have such a small influence on the geometry of spacetime that the difference can't be noticed with small distances. LISA can observe lenght differences in space at the atomic scale. 3) I don't follow... gravity waves are distortions of spacetime travelling at c, and the "frequency" (or the volume of distortion) of the gravity wave depends on what caused the gravity wave. A head-to-head collision by two blackholes would cause noticeable gravity waves. I'm just an undergrad so someone who has actually studied this stuff might answer more clearly.
 P: 15,319 1) As drez ponits out, there's no upper limit on wavelength; it's a continuum. Thge label radio waves is purely arbitrary and human-centric. Everything below 10^7Hz is considered radio. 2) 5 million km is merely a long enough baseline. It has nothing to do with the frequency of gravity waves. 3) Setting gravity aside for a moment, lets just deal with the general topic of wavelengths and frequencies of EM radiation for the moment. There is nothing special about f=1; it is not a lower limit. An EM wave of f=0.5 has a wavelength of 600,000km.
 P: 398 What's the longest wavelength possible? Then can EM waves have such long wavelength that they can never be refracted?
 P: 683 Thanks guys, great answers. Most people reply with either a paragraph about hyper-dimensions and transcendence of space-time mumbojumbo, or with winded answers that show how smart they are but cleverly dance around the question because they are too pompous to admit they don't know the answer. Can I just say, amazing replies and so concise!! Back to Gravity waves.... a) Are Gravity waves like EM waves then? Is there an inifinite spectrum of them possible? b) What wavelength of Gravity wave should we hope to find first if they exist (the one's created by cojoining blackholes), any idea on the expected value of this wavelength? c) If gravtiy waves moves at a velocity = C, then why can't they be considered EM waves? I know EM waves are created by electron excitations or energy level drops, but doesn't it seem like gravity waves are created by the same process or a sub-process thereof, considering both EM and Gravity waves both travel at C? Thanks again, anticipating another great round of replies!! cheers.
 P: 398 c) "gravity waves" would be "created" by Higgs particles, not electron excitation or deexcitation. The wavelength issue depends on the Higgs particle, which we have yet to prove experimentally, so further speculations may prove futile.
 P: 683 What is a Higgs particle? Why is it inferred from theory and how?
 P: 398 My favourite page on Higgs is: http://hands-on-cern.physto.se/hoc_v21en/index.html Click on the link "Higgs" in the left scroll menue and you will find what you are loooking for. In short, you could say that the Higgs particle is neither a force carrier nor a matter particle. It appeared in the equations of the Standard Model when these where changed to allow particles with mass.
 P: 15,319 In short, the Higgs field is the closest thing to the pop term "the fabric of space". The Higgs field supposedly causes a form of "drag" on matter, and thus is the source of the property of mass.
 Mentor P: 7,315 The relationship between wavelength and frequency is: $$\lambda = \frac c f$$ Now if you were to take a perament magnet and wave it up and down once per second you would be creating an electromagnetic wave with a freqence of 1 Hz which would have a wavelength of 3X108m. The Extremely Low Frequency band (ELF) 3 - 30 Hz is used to communicate with submarines when they are submerged.
P: 2,292
 Quote by Integral The relationship between wavelength and frequency is: $$\lambda = \frac c f$$ Now if you were to take a perament magnet and wave it up and down once per second you would be creating an electromagnetic wave with a freqence of 1 Hz which would have a wavelength of 3X108m. The Extremely Low Frequency band (ELF) 3 - 30 Hz is used to communicate with submarines when they are submerged.

Whoa... Hold on a second here.
Are you suggesting that I can take my grade N38 neodymium magnet, vibrate it laterally at 10 cps, and generate an emmited 10 hz EM photon field?
 Sci Advisor HW Helper P: 1,333 What are talking about, Order? If you tell me which of your questions didn't get answered to your satisfaction I will try to remedy the situation.
P: 15,319
 Quote by Chaos' lil bro Order Please don't take this as an insult, but why do PF 'mentors' always dodge the tough questions and post simple, irrelevant replies when they don't understand something? Can we release our egos ...
Ah. You wish to insult mentors (I refer specifically to the ego comment) - but ask them not to take it as an insult.

I guess that's kind of like getting questions answered and then claiming they weren't answered.

Perhaps you could be more specific.
Actually, never mind.
P: 2,056
 Please don't take this as an insult, but why do PF 'mentors' always dodge the tough questions and post simple, irrelevant replies when they don't understand something? Can we release our egos ...
Even if you think they don't answer the questions well, unarguably mentors teach you a lot, and give you a good background, that's why they were chosen to have the title under their name.

mentor - to serve as a teacher or trusted counselor; a wise and trusted guide and advisor
Mentor
P: 7,315
 Quote by pallidin Whoa... Hold on a second here. Are you suggesting that I can take my grade N38 neodymium magnet, vibrate it laterally at 10 cps, and generate an emmited 10 hz EM photon field?
Yes, that is what I mean. But wait, what is a "photon field" I have never heard of that. I mean that if you wave your magnet at 10cps you will be generating photons of the given wavelength, I will trust your math.
 Mentor P: 7,315 Chaos, I answered your question about electromagnetic waves. Since Gravity waves remain undetected and so far are purely theoretical constructs I did not even try to touch that part of your question, because you are correct, I don't know.
 P: 196 Something offered freely upon request should be accepted or rejected graciously. The value a gift possesses when offered is retained only when its value is appreciated by the recipient. The price of knowledge is not fully paid by accumulation but by assimilation. We are indebted not only to those who convey knowledge but to those who first acquired it from whom they learned through respect and admiration. Those who discover knowledge have paid their debt in full by conformity to the reality that enabled them to explore it. Knowledge is the food the mind requires to obtain the food the body requires to sustain the mind. In other words, “Don’t bite the hand the feeds you”, if you prefer food to poison. What's the longest wavelength possible??? About that long. See why I am not a mentor? Can you appreciate the difference? Integral, Loved your broadcast! Received it load and clear.
 P: 683 Ok, ok, sorry. I think you know why I was frustrated. Anyhow, anyone have a guess as to a process arising from within an atom that may cause a graviton to be emitted. I'm thinking along the lines of an exotic particle being deexcited at a level even smaller thean quarks, which would produce a graviton, analogous to how an electron deexcitation creates a photon. Can anyone rule out this theory with already established axioms? Or is it at least plausible, even though it is currently unprovable? Again, sorry for the earlier comment. Maybe moderators should strike it and the replies to it from the board, so it doesn't dilute the interesting topic at hand.

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