Prime Time Replay:
Astronomer Mark Dickinson
on Recent Discoveries in Deep Space
MsgId: *infinities(8)
Date: Sun Apr 27 22:03:51 PDT 1997
From: Melanie At: 206.80.181.190
Good evening. We are delighted to have with us tonite, Mark Dickinson, who hails from the Baltimore Space Telescope Science Institute and Johns Hopkins University. His area of expertise is origins of the universe, and he's here to help us better understand some of the fascinating new developments in the field. Welcome Mr. Dickinson and audience.
MsgId: *infinities(9)
Date: Sun Apr 27 22:05:11 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
Hello Melanie, and everyone staring at their screens out there.
MsgId: *infinities(10)
Date: Sun Apr 27 22:06:11 PDT 1997
From: Melanie At: 206.80.181.190
Recently, cosmology and astronomy have been very much in the news -- barely a week goes by without a front-page revelation. Is it mere coincidence that all this is happening at once? Or, have we reached a critical watershed in the study of the universe?
MsgId: *infinities(11)
Date: Sun Apr 27 22:08:09 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
We're fortunate to be living at a remarkable and critical time for astronomy -- a time when we are really beginning to get a glimpse of the "big picture," or at least we think we are. A lot of the attention has come because of the remarkable new telescopes and instruments we have now -- especially things like the Hubble Space Telescope (HST) and new giant telescopes on the ground.
MsgId: *infinities(12)
Date: Sun Apr 27 22:09:32 PDT 1997
From: Melanie At: 206.80.181.190
What have these new technologies and techniques enabled us to see and do that we weren't able to before? How has this affected your field?
MsgId: *infinities(13)
Date: Sun Apr 27 22:11:42 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
You'd need about 100 astronomers on this show at once in order to do that question any real justice! For the moment I'll restrict my answer to the field in which I work -- observational cosmology.Ten or fifteen years ago, we knew very little about the universe outside our own local vicinity. I'm using "local" in the rather careless way astronomers do -- local means only the nearest billion light years or so! But on the grand scale of the universe, that's our neighborhood, and the galaxies we could find and study were sharing that volume of space with us. Now, however, we can actually find and study galaxies out to distances of 10 billion light years or more, and trace their evolution across maybe 80 or 90 percent of the history of the universe!
MsgId: *infinities(15)
Date: Sun Apr 27 22:18:48 PDT 1997
From: Melanie At: 206.80.181.190
One of the latest headlines dealt with news about the age, mass and fate of the universe. What have scientists discovered that is so exciting?
MsgId: *infinities(16)
Date: Sun Apr 27 22:22:57 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
We have several ways of trying to estimate the age of the universe. The major quest is to measure the rate at which the universe is expanding -- as we look out to distant galaxies, we find that they are all moving apart with speeds proportional to their separations -- the whole universe is expanding. If we know how fast it is expanding, then we can "work backwards" from the present and figure out when it all started -- when the Big Bang took place.
MsgId: *infinities(17)
Date: Sun Apr 27 22:32:02 PDT 1997
From: Melanie At: 206.80.181.190
Doesn't this presume that the universe expands at a constant rate? Can we assume that?
MsgId: *infinities(20)
Date: Sun Apr 27 22:39:25 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
No we can't assume that -- in fact, the gravity of all the matter in the universe should slow its expansion gradually, and this is one of the other uncertainties in calculating the age -- we also need to measure the rate of deceleration. That has another important consequence -- will the universe slow down enough so as to eventually recollapse, or will it keep expanding forever? To answer that, we need to know how much "dark matter" is out there -- it seems that maybe 90% or more of the mass in the universe is invisible to us! That makes it rather hard to understand its ultimate fate until we figure out what that dark matter is.
MsgId: *infinities(21)
Date: Sun Apr 27 22:42:02 PDT 1997
From: Melanie At: 206.80.181.190
We hear a lot about the Big Bang -- very dramatic stuff. But what happened next? What was the universe like early on? How did it progress?
MsgId: *infinities(23)
Date: Sun Apr 27 22:59:24 PDT 1997
From: Mark_Dickinson At: 206.80.181.190
Early in the history of the universe, it was a sea of energy and particles, and as it expanded, the universe cooled down, but was still very smooth and uniform. Somehow gravity caused small fluctuations in the early universe to collapse and grow and gradually all the structure that we see around us today, stars, galaxies, clusters of galaxies, congealed out of this primordial soup of matter and energy during the last 15 billion years.Now the amazing thing about the past few years has been that we have actually been able to find and study galaxies in the universe when it was young -- by looking farther and farther away, we are looking back in time and seeing galaxies when they were young. We can now find galaxies all the way back to the first 10 to 20% of the universe's history, and catch them in the act of formation. With Hubble, we can get sharp images which let us study their structure, and we can survey the process by which galaxies like our own may have formed.
MsgId: *infinities(26)
Date: Sun Apr 27 23:08:15 PDT 1997
From: Melanie At: 206.80.181.190
The other recent excitement in the field was generated by researchers who said their calculations pointed to there being an "up" and "down" in the universe. How did they figure this out? Why is this discovery so surprising?
MsgId: *infinities(27)
Date: Sun Apr 27 23:12:47 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
That's a strange result indeed -- strange and controversial. It is one of the pillars of modern cosmological theory that the universe is homegeneous and isotropic on large scales -- that is to say that when you look out far enough and average over local inhomogeneities, the universe is on average the same in all directions. But the study you mention seemed to find an indication of a preferred direction in space -- or some other effect which could explain why those researchers detected a particular signal in the polarized light from galaxies around the sky. If they are right, then it points to new physics that we don't yet understand, but I would caution that it's an unverified observation so far -- something that needs to be checked by other groups. That's the way science works -- radical claims have to be rechecked independently.
MsgId: *infinities(28)
Date: Sun Apr 27 23:15:22 PDT 1997
From: Melanie At: 206.80.181.190
What are some of the great myths and misconceptions about the universe and the way it behaves?
MsgId: *infinities(33)
Date: Sun Apr 27 23:39:57 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
One is that the Big Bang took place "somewhere" -- in a particular place, a "center" of the universe, and that we are all rushing away from it. Instead, the Big Bang really took place *everywhere* at once -- all points in our present universe were together at the beginning.When the Big Bang took place, the universe came into being and has been expanding ever since -- but there is no center where it all started. The evidence for this is the homogeneity and isotropy I mentioned before -- when we look at microwave frequencies with radio telescopes, we see a uniform glow of radiation everywhere -- the relic afterglow of the Big Bang. This is *extremely* smooth and uniform, showing that the early universe was smooth as I described it earlier. The small fluctuations which were measured with (e.g.) the COBE satellite were the seeds out of which all structure today, including our galaxy, eventually grew.
MsgId: *infinities(22)
Date: Sun Apr 27 22:46:25 PDT 1997
From: guest At: 166.72.178.243
How many cycles has Hale Bopp made?
MsgId: *infinities(29)
Date: Sun Apr 27 23:17:53 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
I'm sorry to say that I don't know! Probably no one does -- it's hard to judge how many times a comet has passed through our solar system before. But Hale-Bopp is extremely massive, suggesting that (1) it could last a long time, many passages, but also that (2) it may be a relative newcomer to the inner solar system -- if it had been past the sun very many times before it would probably have lost more of its mass and be smaller now. But I'll admit that comets aren't my field -- you'll have to invite a comet expert on the show another time.
MsgId: *infinities(30)
Date: Sun Apr 27 23:22:41 PDT 1997
From: Melanie At: 206.80.181.190
What are you working on now?
MsgId: *infinities(36)
Date: Sun Apr 27 23:41:58 PDT 1997
From: Mark_Dickinson At: 130.167.102.31
Well, other than trying to figure out how this chat-room software works, I've spent much of the last two years working with an observation called the Hubble Deep Field -- the deepest view of the universe ever obtained with an optical telescope. In December 1995, we trained the Hubble Space Telescope on a tiny patch of the sky for 10 continuous days and just kept snapping pictures non-stop. Then we combined these together in computers to produce a single, multicolor image which reaches billions of times fainter than you can see by eye. In a space only 1/140th the size of the full moon, we can see roughly 3000 galaxies -- some seen nearly 90% of the way back to the time of the Big Bang. More than enough to keep us busy!
MsgId: *infinities(38)
Date: Sun Apr 27 23:45:18 PDT 1997
From: Melanie At: 206.80.181.190
That about wraps it up for this evening. Special thanks to our guest, Mark Dickinson, for staying on into overtime with us, while we sorted out the technical glitches. And, as always thanks to the audience for joining us for Infinities. Good night.
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