OT for other dark matter 'fans'.

George Herold did read

We urgently need an other probe than EM radiation. LIGO will teach us some things I hope. And we should send probes looking for other planets, see what the frequency shifts tell us, even to verify current assumptions about redshift and bang. And .. has a whole youtube presentation about multiple bangs. (.. cannot remember his name). So if (EM?) signals from one bang are present in the other then what.

For me it is clear, 'time started' is bullshit. As there are more planets than earth, there are more stars than our sun, there are more bangs than what they carry on about.

Maybe dark matter does not even exists, maybe grey matter well :-) Dogma Einstein worshiping, peer reviews, expensive money grabbing, magazines.

Would be interesting to look what theories we have a million years from now, or maybe there will be no humans, just mosquitos.

But, we need to go, to space, now.

Hi Jan, There is this 'debate' going on in cosmology/ astronomy about dark mater and MOND (modified gravity) I'm just an interested observer; But my understanding is that CDM (cold dark matter) fits with models of the early universe, (ripples in the CMB (cosmic microwave background)) And that MOND makes a simpler fit to galactic models.

The nature paper finds too much (21cm) absorption for dark matter models. (Though they are looking for a signal that is hidden in a background that is 1k times larger...so might still be some calibration error... there is some nice stuff here.

Anyway the blog author observes that it fits nicely with a 'no CDM' which is very interesting.

George H.

George Herold wrote

I am aware of that, been following that for years. Although the MOND theory, actually just an equation fix of Newton's, is often shown correct, cases have been found where it is not.

There are other theories to explain red shift too, tired light was one of those. Whole arguments in sci.physics when it was still about physics (stopped reading it).

That is nice, did you have anything to do with that electronics?

I have seen some nice presentations and an interview with Roger Penrose on youtube, he is easy to listen too.

Why Did Our Universe Begin? - Dr. Roger Penrose - (Closer to Truth Interview)

Are we Seeing Signals from Before the Big Bang?" - Professor Sir Roger Penrose OM FRS

There is more, and there are also lectures from

There are also lectures by Leonard Susskind on youtube, he reminds me more of my physics teacher...

It seems some of Dr Penrose's theories regarding things we should see when there are multiple bangs are confirmed. There is a lot of philosophy, that is good, we need that,

China now has the biggest radio telescope China's FAST telescope identifies 43 pulsars

Right. I figure it's the second order term in some better gravity equation... lamda (dark energy) being the first term. We need the next Einstein. :^)

Nothing... I just found out about it from the trintonstation blog.

Though it's pretty cool... you have to follow the redshift of the 21 cm line.. 1.5GHz down to z=~10, ~150 MHz. with some range so 500 - 50 MHz. We (someone) should launch a ballon or rocket to look..

A receiver on the dark side of the moon would block a lot of the Earth's RF interference.

OK I know little of Penrose. I've watched a bunch of Susskind's videos. (fun stuff)

What's the frequency range?

George H.

Penrose is interesting but perhaps a bit too willing to use his imagination.

I've got a copy of "The Emporer's New Mind" and I think I've bought and read "The Road to Reality" though it's not on our bookshelves here in Sydney.

A week or so ago I was walking through a C.M.Escher exhibition in Friesland (in the Netherlands) and got reminded of Penrose tiling, which influenced some of Escher's quasi-tesselations.

Penrose is more a mathematician than a physcist.

--
Bill Sloman, Sydney

I didn't realise it was that way round!

A couple of years ago there was the first(!) MC Escher exhibition in the UK. It was well worth seeing, not only to be able to examine originals close up, but also because the explanations were enlightening - an example of excellent curation.

I've been entranced by his works since I first saw them in my early teens in, of all things, one of my mother's magazines. There's a lot to be said for boredom during school summer holidays expanding minds.

Now you just wait until astron[a]uts from all countries in the world start hopping around there with their walkie-talkies :-) China has interesting plans to put a satellite at the back side of the moon for communication with them astronauts

I do not know exactly, but from a 500m diameter disc one could infer it could still focus 6m (50 MHz) waves. But no idea what sort or receiver they use, and if it covers that band. Google and wikipedia to the rescue:

70 MHz to 3 GHz likely because the illuminated diameter is a bit less than 500m, is 300m.

Huh, how do you get from 500 m diameter to 6 m waves? (I know little about antennas.)

Well that is a perfect range. Though the big problem may be interference... which is why the EDGES thing is in the middle of nowhere... (Western Australia :^)

George H. (me mum was from Perth)

George Herold wrote

50 MHz = 6 m

Now imagine a large mirror, 500m, and 6 m long waves hitting it. Mirror is much larger than wavelength, a reflection pattern will form.

Same for audio, say ultrasound 44 kHz, just a small parabolic mirror will focus that sound.

Same for satellite dishes, say 10 GHz, 3 cm, a 300 cm dish will work wonders, many are only about 87 cm, like the one I have. Very narrow beam really, just point 1 or 2 degrees the wrong way and you lose signal.

lightning is: Do Not Wear Headphones Connected To Dish When Lightning Happens.

Yes, nice place for an antenna, somewhere in the boonies I still hope to see somebody receive alien TV programs... That would change a LOT of things. We see signals transmitted with modern modulation systems look more and more like white noise. We see tons of noise from the universe, it is very possible alien signals are not only part of that, but maybe even a cause of that. We use these modulation systems for better spectrum efficiency. The math needed for decoding can be the big challenge. I coded some dvb-s and it gives you a good idea what is involved.

DVB-S is also what the voyager spacecraft uses. But who knows, bit of luck is also needed, and political will to admit it,

Hmm, does it ever bother you that the transverse 'size' of a light wave is approximated by it's wavelength? (which is it's length in time, so to speak.) I always get a little weirded out when I think of tiny little atoms emitting or absorbing 'big' light waves. Worse still is proton NMR, flipping a tiny nucleus with ~MHz 'light'.

George H.

Yes, atoms absorbing and re-emitting energy: From

Mechanism In classical electrodynamics, light is considered as an electromagnetic wave, which is described by Maxwell's equations. Light waves incident on a material induce small oscillations of polarization in the individual atoms (or oscillation of electrons, in metals), causing each particle to radiate a small secondary wave in all directions, like a dipole antenna. All these waves add up to give specular reflection and refraction, according to the Huygens-Fresnel principle. In the case of dielectrics such as glass, the electric field of the light acts on the electrons in the material, and the moving electrons generate fields and become new radiators. The refracted light in the glass is the combination of the forward radiation of the electrons and the incident light. The reflected light is the combination of the backward radiation of all of the electrons. In metals, electrons with no binding energy are called free electrons.

so the forward radiation cancels the incident light, and backward radiation is just the reflected light. Light-matter interaction in terms of photons is a topic of quantum electrodynamics, and is described in detail by Richard Feynman in his popular book QED: The Strange Theory of Light and Matter.

Is not 'atoms absorbing' just resonances? Electrons kicked to higher orbits?

In a mirror you _reflect_ the wave, it bounces of the surface in some specific angle, the usually parabolic mirror is formed so the reflected waves all focus on some point.

the wavelength is much much longer than the size of the atoms the reflector (dish) is made of, there may actually be holes in the mirror, as long as those are smaller than the wavelength. You can make one from chicken wire for HF. My satellite dish is an offset dish, so the receiver in the focal point (LNB Low-noise block downconverter) does not cause a shadow on the reflector.

Acoustic mirrors are much the same, there it is air pressure variations,

Molecules may heat up a bit will vibrate?

Same with the mirror in your flashlight (also EM waves) and in your car headlights, but there the wavelength is much shorter, the atoms say in place (one hopes).

Math, play, neural net, understanding.

Filosphy.. Learning :-)

The geosynchronous satellites are spaced 2 degrees apart. If you're off +/-2 degrees, you're looking at the next satellite. At 12GHz, the a 1 meter dish has a -3dB beamwidth of about 1.8 degree, which covers about 1/2 of an orbital slot at +/-0.9 degrees. Therefore, the largest aiming error possible would be +/-1.1 degrees. +/-2.0 degrees won't work. I use +/-0.5 degrees accuracy and stability when aiming DBS dishes.

Fun and games on C-band (3.7 to 4.2GHz): The 3, 4, and 5 meter diameter dishes are nothing compared to the 500 meter FAST monster, but are still a serious challenges to aim and stabilize.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

On Monday, August 13, 2018 at 1:40:59 PM UTC-4, snipped-for-privacy@nospam.org wrot e:

r it could still focus 6m (50 MHz) waves.

wave, which is described by Maxwell's equations.

tion in the individual atoms (or oscillation of electrons,

ll directions, like a dipole antenna.

ding to the Huygens-Fresnel principle.

t acts on the electrons in the material,

tion of the electrons and the incident light.

of the electrons.

,

ion is just the reflected light.

rodynamics,

he Strange Theory of Light and Matter.

ts? Right, but atoms are tiny ~1nm and light is huge ~1um... how does that work? (rhetorical question) Anyway it's mostly just me trying to think of quantum things classically. This is OK

George H.

cific angle,

n some point.

or (dish) is made of,

han the wavelength.

LNB Low-noise block downconverter)

eadlights,

es).

work? (rhetorical question) Anyway it's mostly just me trying to think of quantum things classically. This is OK

Metals have much greater extents than ~1nm. There is effectively a continuum of wavenumbers that are populated in any given metal, with the highest wavenumbers (lowest frequencies) corresponding to overall length, as we would classically expect.

Note that goes for the system-level, far-field approximation. For near fields and direct current, of course, continuous electron displacement or flow is also a thing.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

Jeff Liebermann wrote

Very impressive, do you do anything with the Oscar sats?

I had the plan to try an ATV uplink / downlink test when the Qatar Eshail-2 was launched, but that sat launch has been delayed again and again.

However it seems SpaceX now has it?

I have nice 2.4 GHz linear now:

and a few LNBs I want to modify the ceramic oscillators of for the right ham frequencies. But the whole thing moved from the lab table after waiting for 2 or 3 years for that launch to happen. Need a bigger dish too for the ATV uplink, will it ever happen? We just had an other code orange storm, flying dishes is not what I want.

But if it ever launches I will first see if I can get the narrow band signal with my movable disk. It is geostationary sat, a whole new thing for ATV.

OK site indeed. I look at it (Einstein now rolls over in his grave) as a ball on the water No matter how long the wave (length), the ball will move up and down with it. I know E says no ether, about the M&M (not the candy) experiment, etc but there is a medium, else why Mu0, physics now talks about virtual particles popping in and out of existence, but 'virtual' and 're-normalization' is a hint they got it, as also often happened in history,

100% wrong. I was reading this today:

Right. But take something like a Rubidium atom. (Well I've got a bunch of them so I sorta know about them.) Atomic radius is ~0.3nm but the cross section for absorption of resonant radiation. (S-P transition of the outer electron) is something like the wavelength^2 (divided by 2*pi or 4 or some term like that.) Where the wavelength is ~795 nm. Where for something like Rayleigh scattering the cross section is tiny.

How big a photon is, is something that has always bothered me a bit. I guess we only 'see' photons when the interact with something else.. and so it's mostly the 'something else' that sets the size.

George H.

Hmm I've heard people talking about accelerating electrons with lasers for a long time. Getting all the timing right is the hard part. (linear accelerators are kinda a string of microwave cavities.. with the microwaves put in at just the right time and phase... doing that with light waves is harder.) but who knows maybe they have some good ideas.

George H.

Yeah, high Q resonators couple much more nicely, don't they? :)

The classical equivalent is a very small, very narrowband, but still reasonable gain antenna. Like a Tesla Coil (but designed for enough Q (and not sparking) so that the far field radiation resistance dominates its real component).

Well, photons have zero mass, while everything else has nonzero, so, the de Broglie wavelength certainly works out that way. :) The atom might be very small, but convolved with the photon PSF, you can't tell.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/