Date: June 27, 2009
Title: Cries From the Infant Universe
Podcaster: Richard Drumm
Links: For more information on this topic link to Dr. Whittle’s home page at UVa: http://www.astro.virginia.edu/~dmw8f/
From here you can link to The Teaching Company site where you can order the 6 DVD set titled “Cosmology: The History and Nature of Our Universe” which features Dr. Whittle lecturing extensively on the subject. At the UVa site you can also download the sound files heard here, PowerPoint presentations and much more. The December 3rd podcast will have more from Dr. Whittle on the CMB.
Description: One of the most impressive developments in modern cosmology has been the measurement and analysis of the tiny fluctuations seen in the cosmic microwave background (CMB) radiation — the omni-directional wall of hot glowing gas which dates from when the universe was only 400,000 years old.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He’s found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
Today’s sponsor: This episode of 365 Days of Astronomy is brought to you by NRAO.
And thank you again to George Hrab for that wonderful musical introduction. If you don’t listen to the Geologic Podcast yet, why, you should! Hello, I’m Richard Drumm, President of the Charlottesville Astronomical Society here in Charlottesville, Virginia, with Professor Mark Whittle of the University of Virginia Astronomy Department. Hello Dr. Whittle!
Tell me, astronomers have been studying the microwave background, the CMB or CMBR for almost 40 years now, what exactly is it and why is it so darned interesting?
I think a good way to begin to look at what the microwave background is, is to remember this fantastic privilege, I suppose that astronomers have, which is that they’re able to see history directly. Simply by looking very far away you’re inherently looking back in time because it takes so long for the light to cross the universe from distant objects.
So if you look 14 billion light years away you’re looking back in time 14 billion years. What you see when you look 14 billion light years away is the big bang itself, and so all around us then in a sort of 360 degree panorama at enormous distance sits this big bang image.
And of course, I’ve just used the word image there, so one wants to know well, ‘What did the big bang look like?’ and one of its defining characteristics is that it was incredibly bright. In fact, in a way, a better term would be the big flash rather than the big bang.
In the 14 year journey that the light waves have taken to cross space during that trip they’ve been stretched by a factor of 1,000 because the universe is also expanding. So they started out as light with a wavelength around 1 micron, a millionth of a meter, and if they’ve been stretched 1,000 times they arrive at a thousandth of a meter or a millimeter. Now that’s actually in the microwave part of the spectrum.
So the cosmic microwave background is our vision of the birth of the universe. And to be strictly accurate, it’s actually a time about 400,000 years after the big bang itself.
And so the WMAP image-and if you go to Google/images and type in WMAP you’ll see this oval with green and yellow splatters on it, that is, basically it’s our baby picture!
Yes, and that immediately tells you why astronomers are so interested in looking at the microwave background. It’s 400,000 years after the big bang. There were no structures like stars or galaxies, there was an incredibly uniform, hot glowing gas. And there was a very, very slight texture or roughness to it, regions of slightly higher and lower density and pressure and temperature.
It contains a great deal of information and it will determine in large part how the universe of galaxies and stars will then ultimately grow and form. And it also contains information that comes from a much earlier time, in fact the launching mechanism itself.
I suppose with a name like ‘the big bang’ that with that word ‘bang’ in it, that it would be some sort of sound involved in it. If that was the case, what would it have sounded like had we been there at the time and had a really good spacesuit?
Yes, yes, you would need a good spacesuit because back at that time about 400,000 years after the big bang you would have been incinerated in probably a few seconds. It’s basically a bit like diving a few kilometers into the Sun’s atmosphere, it’s very, very bright from all directions, you actually…
RBD: Rather uncomfortable!
Yes. Of course ‘an explosion’ is a bit of a misnomer for the big bang, And the reason explosions are loud is because they send outwards a pressure wave so it’s an expansion into a pre-existing gas or atmosphere. Of course the big bang is different from that, it’s and expansion OF space with all its contents. It’s not moving into anything, it’s just an expansion of space itself with matter and energy embedded within it.
So, ironically, the big bang itself was pure silence. By the time of 400,000 years indeed, sound had developed, and there was quite a cacophony. And one way of viewing the patches on the microwave background is as the peaks and troughs of sound waves.
The waves are actually very long, they’re many thousands of light years, and so they correspond to frequencies, pitch which is very, very low by human standards, roughly 50 octaves below human ears. But nonetheless actually you can shift them up in pitch by the 50 octaves and put them into the human audio, audible range.
You can actually recreate this sound, and so let’s play it, here’s just 10 seconds of the sound.
So, it’s, it’s sort of a raw, deep roaring sound. And in fact, our ears aren’t able to quite pick up out of that sound what is really quite an interesting sound spectrum. If you analyze all the different frequencies present, then you generate a thing called a sound, sound spectrum, you can think of it a bit like a light spectrum so it’s intensity versus wavelength, in this case it’s wavelengths corresponding to pitch.
When you do that, when you analyze the number of different waves present, long, medium and short, you find quite a remarkable sound spectrum shape. In fact, it looks like a cross between noise and a musical instrument. There’s actually musicality present in the sound.
The “Music of the Spheres!”
It’s funny that it evokes that, you know, important historical term “The Music of the Spheres” that of course was linked to the solar system and the orbits of the planets and their various ratios. This, in this case it’s actually a natural process in the early universe which leads to the presence of certain wavelengths being stronger than other wavelengths.
And so there are, actually a fundamental and harmonics are also present, just as you would get if you took the sound spectrum of a musical instrument. There’s a primary tone and then a higher set of roughly equally spaced harmonics.
If we follow the sound forward in time a rather wonderful thing occurs, which is that in a sense the peaks of the sound waves gradually turn into the first generation of stars, while the troughs in the sound waves evacuate out and become the gaps between stars. The stars then, of course, gather ultimately to make galaxies.
So the current universe that we now find ourselves in is a sort of relic of this acoustic era. Recently the Sloan Digital Sky Survey and also the Australian group, the 2 degree field survey, have just mapped out the position of about a million galaxies over a region about 2 billion light years in radius.
And so these galaxies are not spread about uniformly, they actually make a fascinating, weblike pattern. But etched in that pattern if you analyze that a little bit like you analyze the microwave background, you can see that fundamental and harmonics still present sort of etched in the pattern of galaxies.
What kind of things have we learned by studying the cosmic sounds, and how is that done?
So it’s actually very easy to sort of see the basic approach here. The sound that any object makes tells you really about the nature of the object. So I’m going to actually hit two objects here…
And here’s the second one.
Quite different, yes!
So they’re quite different, and even if you were not here looking at these objects I’m going to guess you could probably tell the first one was a wine glass and the second was just a mug, a cup. And so if you took a sound spectrum, and if you were knowledgeable about the way in which objects vibrate you infer the size and shape of both of those two objects.
And it’s exactly the same with the cosmic sound. If you listen, or in fact just analyze the sound spectrum, you can tell what the structure and properties of the universe are. Perhaps the most important contributions that the microwave background’s made is to measure using the tone, using the basic pitch of that cosmic sound, measure the geometry of the space.
And it turns out to, delightfully, that the space is, has the geometry that we all learned at high school, which is Euclidean geometry.
It’s the geometry that you do on a flat piece of paper, and in fact in that case the angles inside a triangle do add up to 180.
Thank you, Dr. Whittle, for making all this crystal clear!
You’re very welcome, Richard, that was, thank you for interviewing me.
End of podcast:
365 Days of Astronomy
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