December 26, 2019 0

The Fruits of the Tree of Astronomy Phillip Morrison


I hope you can all find
comfortable positions to listen, as it comes
as no great surprise to see an overcrowded hall for
this particular day of lecture. I have only a few words to say. I think one of the functions
of the introductory speaker is to wait until the
crowd quiets down. And I hope I won’t speak
much longer than that. But I do have a few comments
that I would like to make. We meet this afternoon on
behalf of the faculty of MIT to honor two individuals
of whom we’re very proud. And one of those
is the individual for whom the lecture series
is named, Dr. Jim Killian, who once again honors us with
his presence here today. The faculty of 1971 established
this lecture series in tribute to Dr. Killian and his concern
for the excellence of MIT. I was thinking, as I was
going to remark today, that all of us who teach each
fall, often have that feeling, the freshmen are getting
younger each year. And I wonder if Jim feels
the Chairman of the Faculty are getting younger each
year, because I was certainly a young sprout when
he relinquished the reigns of the
institute and became chairman of the corporation. But I think many of us who
have lived and grown up during that period have quite
an appreciation for the affect that he had on [INAUDIBLE] [APPLAUSE] I hope you all were able
to get your homework assignment, The Little Red
Book, because it will give you all the facts about both the
award and the speaker today, and I’m not going to
repeat any of those. I do have a function, which
is to present Phil Morrison a tangible award of this. He already received
the more tangible part, the check, some
time ago, so he’s had both the use and
the interest of that. But today, I would like to
present the scroll, which let me quote, “The
end of, in recognition of his contributions to many
fields of physics, especially astrophysics, to his long
distinguished career. His originality and
productive insights have inspired and delighted
his professional colleagues, generations of students,
and countless followers of his stimulating
interpretive reviews of science and technology
for general audiences–” [INAUDIBLE] Thank you, very much. [APPLAUSE] If I could take one more
minute of your time, I’d just like to comment. One of the things I
said to my class today, is that there are events
in MIT which happen rarely, and you should be pleased
to be here when they happen. Don’t miss them. I think there’s going to
be one this afternoon, and I’m sure we will find
that true at the end. The other thing I
wanted to comment was that in inviting
people to come, those letters went
out over my signature and many people couldn’t
be here today replied. One of Phil’s former
students replied, and I wanted to quote to you a
couple of sentences from that, because I think it’s important. At least I want to
do it, all right? I will share the whole
matter with Phil later, he hasn’t seen these. But these are just
two sentences that struck me as a kind of
tribute that any of us would certainly be more
than proud to have. Referring to lunches
that they used to have when you walk in
the Physics Department, “Phil’s comments served to
cajole, provoke, and enliven the group, and I feel
certain that most of us who attended those
discussions extracted more from our own minds
than we possibly could have in any other way.” Which sounds to me like the
best description of a teacher I’ve heard recently. And the other is, “The quality
that I admire most in Phil is his tenacious affection for
the world in the face of all its imperfections. Phil’s life is a testimony
as much to the human spirit, as to the human intellect. By honoring him, the faculty
members of the institute do themselves proud.” [INAUDIBLE] [APPLAUSE] Thank you, very much. It’s obviously a
moving occasion. And indeed an honor. One bestowed by so many
predecessors, teachers, colleagues, and students. Many people being more than
one of those categories at the same time. So I’m properly moved. And I should like to,
however, come to the matter at hand, since it is not
only a ceremonial occasion but I hope one which
will be of interest. [INAUDIBLE] The metaphor that will perhaps
run the entire show this week and next week is something
about science as a tree, as a living, virgining tree. Very Complex, very
difficult in many ways. Very protean, with many sides,
fruit both good and bad. Next week, on the
text, I shall try to describe in primarily
scientific language, one of the principal fruits of the
current branches of astronomy. The marvelous story
we can now tell. The great incompleteness
about the nature of the galactic
world that we see. It’s striking. We can still tell
quite a lot, buts it’s still far from complete. Today however, I want
to look at the tree in a much wider context. I will, I think,
try to discuss one of its most important
fruits and the methods that go with it, in the vexing
domain of cosmology, the study of the
universe as a whole. And I hope to show something
with no formulae and very few graphs, to give some idea of
the logical structure and be tantalizing, I would
say paradoxically, conclusion to which we have
been very reluctantly drawn in the recent considerations,
largely due to work [INAUDIBLE]– And the genetics of a
tree, how can [INAUDIBLE] to grow after all? Which of course is a statement
about the future, the future of our society, of our
species, because it is young people who represent– however worthy the old
folks are who get awards, it’s the young people represent
science as it is coming, not as it has been. So that’s what I
want to talk about. And I have divided the
talk into three pieces. And I was moved somehow
in the last few days, thinking about, because
of the very recent death of my old graduate school
friend and colleague, Frank Oppenheimer himself
the last senator two years one of the most
distinguished contributors to the worldwide
solution to the problems of proper education in science. He had on his wall, always in
the office the last few years in San Francisco,
a quotation which I was not clever enough to
memorize, but I can paraphrase. Very bad poetry for
poetry, paraphrasing, but what can I do? It’s a witty remark
by Ariel [INAUDIBLE], who spent much time
in that museum. And it describes– some
of you will have read it. It describes her
perception of some scene on the coast of Maine
when she was at the beach and saw the bay
studded with islands. The characteristic
stacks, or whatever, of the coast of Maine. And she said the islands,
they appear so distinct, but in fact, they’re
connected underneath. The bathers think they are
as separate as themselves And I leave you to conclude
whether the bathers in fact are as separate as they think. [INAUDIBLE] So I’m going with three
islands to the speech today. I hope they are in fact
connected underneath. And I’ll ask you to indulge the
somewhat clear change in pace, because I do believe they
all go towards a common end. So I shall go to it. Now I guess, first
things, the lights off and I’ll try
the first slide. Yes. And admirable slide. Thank you. Don’t darken the room
much, that’s swell. I’m showing a slide here
that many will recognize. It is done by the
wonderful draftsman hand of a famous Cistercian
architectural critic and scholar. Apparently nobody knows whether
[INAUDIBLE] really build any buildings. But he sure wrote
books and drew pictures about building buildings. He was one of the
great figures of whom we know, in the
12th century, when it was hard to get– the
name of the architect was not yet printed
on the building. So there it is. And this is a
picture from his book of drawings, which has come down
to us, very handsome parchment book, with his own inscriptions
in a beautiful hand, in old french, of course. And up here, what you see
is a marvelous machine. It goes without saying, he
never built that machine. [LAUGHTER] But he could certainly
draw it, and he drew it very beautifully. And he says in here, this
machine, if properly built, will go forever, because it’s– [LAUGHTER] –it’s constantly unbalanced. As anybody can see,
speaking more precisely, the center of the form is
not the center of mass, and obviously it’s going
to run around and around with a handedness given by
the designer of the mallets, I expect. And here, a later hand has
written, amen dico, I say amen. He didn’t build it either. [LAUGHTER] Well, this is only to
show, the understanding of perpetual motion and
energy is an old tradition. And people have a
great deal to think about it for a very long time. I am anxious to point out– not widely recognized, but
I think it is conveniently well-documented, and brilliantly
discussed by Joseph Needham, in the first volume of
his famous work on science of civilization in China– that long ago– before there was
an MIT, long, long before that, and before there were the
means that we all know in which mechanical system do our
bidding, one way or another– there was a strange
feeling about mechanisms and certain professors
had issue to [INAUDIBLE] which I could not
work any better myself saying this machine
was not going to work. [LAUGHTER] In spite of the
testimony of quite a few authenticated
experts, one of them was a man who made a
considerable fortune in the rental car industry. And he certified that
it was a breakthrough of gigantic proportions. And then a magnanimous
offer was made by the company through
and ex-officer, an adviser to Senator
Goldwater, in which they offered to give the
government the rights to use this machine for
national defense purposes free as a contribution
to the public good. And the senator’s
adviser, not the senator, said that it was indeed
a very important decision and they were very
happy to see it. But the FCC was not
much moved by this. And by August, the FCC required
in lieu of prosecution, statements by the company that
perhaps these claims were not yet valid. And in the upshot, the
inventor bought back the right for about the
sum he had paid for it. But he did not give up. The next year,
another story appears. Still another jazzy sounding
firm in Southern California, saying that they have looked
into the box and searched it and they were afraid that they
would find a monkey in the box, but there is no
monkey in that box. It works. And hence the statement,
their stock too rose. University of
Oregon– and here, I think they’ve been dragged
in a little bit unfairly. I’ve never read their statement,
this is all newspaper, so I don’t wish to make
an attack upon them– but some adviser to inventors,
some institutional adviser to inventors, looked at various
inventors’ patents and so on, and concluded that
they were valid and they might actually work. I don’t think they were
talking quite about the same thing, because indeed
he did have issued to him, several patents about the use
and manufacturing of hydrogen peroxide, and
various substances. Quite a few things touching
upon energy and water, but not quite confronting
it so squarely as the case I have been making. So I think those inventions
were probably fairly real. Whether they were worth
while, I don’t know. But the remarkable thing is that
by ’81, still full of energy, after everyone else
has abandoned him. After he’s paid a lot of money
to settle the claims that otherwise were going
to be put against him, after the long suits
against the Presley Company and the recovery by
many stockholders, I dare say not all, he issued
an interview with the New York Times in the little
reprise section they had every once in
a while, saying in ’81, I’m still working on it. I’m now adapting
it to automobiles. I think I’ll get 8 to 10
gallons, miles to the gallon, in my little Plymouth
Horizon, once I get the bugs worked out of it. So the indefatigable optimist. I want to mention
two things that are very singular
about this story, because [INAUDIBLE] story. First, the remarkable
language in which at least– again, not in quotation–
but just the story the New York Times reported,
very enthusiastic, by the way, ending saying [INAUDIBLE]. “If they build a
cheap source hydrogen, it would have
immense implicatons to the world economy. Not only could be used as
a substitute for gasoline, but also for home heating fuels
and other energy sources.” Perfectly true conclusion. Perfectly irrelevant
to the issue when you make it out
of water, and not without expending energy. But what did the inventor say? He said using a
laser like device, generate UV
radiation [INAUDIBLE] puts the steam into
oxygen and hydrogen. If then do us the electrostatic
forces that normally bind the electrons and
protons and water vapor to maintain the reaction. These are extra-nuclear
energy, first defined by Niels Bohr in 1922, it says. Here, the reporter
correctly says he’s found a way to use this
energy in the way described is likely to invoke additional
skepticism of other scientists. Then, he says the
reaction starts from the input of
electrical energy from outside the system, battery
electric light, fair enough. This energy is
converted, by using an optical pump and
other components, into large amounts
of UV radiation of a special wavelength,
precisely entailed to ionize high energy oxygen molecules. The steam is intended to be
a reaction chamber, fine. The chamber is for
the radiation, fine. During the ionization,
the electrons are momentarily liberated
from the atoms in molecules. Microseconds later, they’re
recaptured and recombined with the and the
nucleus of the atom. At this point the energy that
was required to ionize it re-appears and radiates away. The radiation ionizes
another molecule. Very soon, a chain
reaction begins that involves
millions and millions of molecules and atoms. Now, you notice
all the elements. It works on a micro scale,
like nuclear energy. So that you can’t expect
to see whizzing gears and balls floating in water. It works because electrostatic
energy– in fact, it says extra-nuclear, something
like it but not quite the same, as nuclear energy. And it makes a chain reaction. Now, all of these
features precisely describe the way in which
most people not involved would have to regard the
reports of nuclear energy when they’re made. Of course, they’re
[INAUDIBLE] all too certain. The trouble is, the essential
point of the release of energy, say from the nucleus, or say
from the water, or anything else, has been missed. And I blame myself,
as much as the rest of my trade, for that we have
not really thought clearly of trying to make clear what is
the essential feature of energy release. And of course, it is plain. I’ve already indicated it. It is not chain reactions. It is not inside the
nucleus or inside the atom. It has not a thing to
do with those things. It has to do with a
change from initial to final state, no
change, no energy release. And the only exception to
this are absolute changes, changes which we cannot
define absolutely, such as orientation, mere
endurance through time, and change of position. That’s about all
you can find, when you’re able to change
and not release energy. Everything else,
every other change, for nature, substance,
shape, and position of two attracting or
repelling substances, all else, every other
change is negligible. But the important
thing is the change when the uranium goes in. What comes out is
not more uranium, even when you have a breeder
reactor, you get more fuel out. It isn’t the same. There has been a substantial
change not present in the balls you saw going through
the water, not present in Mr. [INAUDIBLE] machine, but
present in every authentic way to release energy But I’m afraid
we have somewhat missed that. Most people don’t recognize
that is a significant thing. It is energy that
makes things work. Energy stored can be anywhere. In the micro world,
it can be concealed. And of course, a new
person might find a way to release energy, just as
a new person 50 years ago found a way to release
nuclear energy, 40 years ago. So it’s much the same thing. And I’m not claiming
that we have a way to change it completely,
to end it completely. But I argue that this is
the kind of problem, which I believe we must
direct attention to, if we are to solve the
problem of the general public well-informed on science. There is, of course,
old precedent for this. “The bush burned and
was not consumed,” a clearly miraculous act. And so it says in the good book. So I can quote biblical
support to this proposition. Now, what I want to talk
about for the next third, the next island, is to
expose a little bit, and try to follow the
logic of what I think is the most remarkable of all
the extensions of the idea of energy that we
have yet encountered, an extension which, I have to
admit I don’t absolute, fully understand. But I think I’m
not alone in this. But it’s important
to the world if it should be fully confirmed,
and it is strongly and largely hinted at today. It is certainly remarkable. And it represents a
novelty, as you’ll see, not quite a paradoxical
novelty, one that appears so, in the light that
I’ve just said. And now, let me go
back a little bit to pick up the argument
in this fashion. If I were to say the aether,
especially if I spell it A-E-T-H-E-R, and I do
not mean, of course, the aromatic anaesthetic. I mean the ineffable
something that inhabits empty space, which
is useful for propagating the waves, for example,
of light and radio electromagnetic radiation. The classical aether,
which the physicists of 100 and some years
ago were heavily involved in looking for. Now, with that
particular aether, a substance whose properties,
among other things, included the property of
remaining at rest, when you move through it,
unless you happen to be so unlucky as to
drag something with you. That substance, I think has
disappeared from physics. Its disappearance was
secured by Albert Einstein, and the great changes
of the first decade of this century,
who showed that, indeed, there was
no such rest frame in which light was
preferentially propagated, that light was quite happy
to go in any old rest frame, and that the idea of a
stationary substance, which propagated it uniquely
had to be given up. In fact, if you measure
the velocity of light, you need not
describe how fast you were moving when you measured
it, with respect to anything you might want to point out. It doesn’t make any difference. And this has been
so well verified, in such an intricate
network of ways that very few
physicists would be willing to go back on this
fundamental proposition. But of course, substances are
very good models for aether. But the logic is not tight. It’s not required
that an aether have all the properties of
water, or air, or steel, or anything you might
pick up in a shop. That would be nice. But we’ve exploded it. It can’t have those properties. Particularly, it cannot
be brought to rest, with respect to light. But does that mean that there
is no sense at all in which it’s possible to see physical
properties ascribed to empty space,
to what physicists like to call a vacuum? And I mean the real
vacuum, not the vacuum contaminated with
what’s left over when the pumps have done their best. I mean the real space
in between those pieces. We have known for a
very long time now, since the great days of the
early ’30s, now more than 50 years– when the quantum field theory
got its first realization in quantum-electric dynamics– that there is a sense in which
that vacuum is very real, full of properties. But those properties
do not include the property of
remaining at rest, and being like a substance. They’re quite
different properties. But they still adhere to
empty space, more or less, is the metaphysical argument
that you need something to propagate the
propagand would imply. In that sense, I believe
aether has returned. Physicists are wary
about saying that. And they always call it the
vacuum, or maybe the vacuum stress energy tensor. They never refer to
it as the aether. But that’s only
because they don’t want to raise false notions
that physics is repeating itself fully. It is not. But it is repeating itself,
I would say helically, with accordance to the
times something periodic. We have this idea back again. It’s not the same idea. It’s much less naive. But we seem to have
lots of science for it. Let me spend a few
minutes discussing that, and then show what the
latest result is, which I find very striking and awesome. What is the quantum aether? Well, we take the
most familiar one from quantum-electric dynamics. Because that’s the field
that we understand best. The generalized
quantum-mechanical extension of the great theory of
Maxwell and Lorentz, which, indeed, preserves
the exact formula of Maxwell and Lorentz, in their
appropriate domain, and only deviates from it
when quantum effects must be taken into account. So all those things are real. Now, of course, if I
have an electric field and magnetic field,
it is a vector field. And it can point this way
or that way, or any old way. The same is true
for either field. And it is easy for me to
imagine the following situation, a situation of a highly
fluctuating field, which points in every which
way, such that the mean value, the average value of
the field is zero. Well, we know that in a
vacuum, by definition, there is no electric field. That’s what you call a vacuum. So but we still have
not answered the fact that it might not be that
our measurements, which after all, always
have to average over time and space in
some degree, are just getting the mean result, which
is zero, even though zero is made by plus and
minus, and not by zero in some ineffable, platonic
way, always being zero. I’m not sure that’s a
meaningful statement. But I think the
metaphor of it is clear. The photons, we know
electromagnetic radiation is in photons, sometimes easy,
sometimes hard to detect. They too must average to zero. Have can’t be any
photons present. But indeed, the theory itself
contains the statement that if you know the number
of photons precisely, you cannot then know the
exact direction and magnitude of the electromagnetic fields. Just as you cannot know
position and momentum together in the Schrodinger
theory, so in the QED, quantum-electric dynamics,
an extension to that is made of very similar sort, with
a very similar mathematical basis, and worked on heavily,
just before the second World War, by Bohr and his group,
made fully consistent on a given richness, which is impressive. So everybody now believes that
there is a vacuum energy, which is taken to be zero. Because its mean value of
fields is zero, and no photons are present. It’s empty. But that something is going
on there seems indicated. Because when we
make calculations according to the best
canons of this theory, for measurable
atomic energy states, well, we can do that in simple
enough atoms, say hydrogen. We find that, indeed, a
term is always present, which corresponds to some effect
of this vacuum, which is not the presence of
an electric field, nor the presence of
a magnetic field, but somehow related to
this transient appearance and disappearance of photons
and, indeed, of electron and positron charges,
in the style, which many people recognize
is nicely represented by various complicated
[INAUDIBLE] diagrams. All I wish to say
is that we have reason to believe,
good, the best reason, that there is some meaning to
this fluctuating, tantalizing, transient quality of the vacuum,
which, of course, does not really have any energy,
energy that isn’t there. Be real careful about that. Because of course, if the
field is plus and minus, the square of the field
is not plus or minus. It’s always plus. And since the
electrostatic energy is the square of the
electric field energy, when you calculate the field
energy in the vacuum, you do not get zero, as
you might like to have. In fact, you’re extremely
likely to get infinity. But you whistle and
look up in the corner and say, well, that’s
obviously wrong. So we’ll subtract it. Clever people have found
out how to subtract it in all situations, practically. And so they’re very content. Indeed, an even more
striking residue of this idea appears in this way. If you take two
conducting plates, very smooth and very cool– so there’s no black body
radiation between them– and bring them near each
other, they attract. And you can calculate it. It’s measurable, done
in the laboratory. You have to be very
careful because it doesn’t amount to any
considerable force, except on a micron scale. And it’s really quite
difficult. But it has been done repeatedly. And it gives the right
result. And the strange part is that result can come about
from the following, somewhat naive, but nevertheless
striking calculation. I say space is full of a vacuum
energy, exactly as calculated, according to the principles
of Maxwell and Dirac. But when I put a little
pair of plates in there, they truncate the vacuum. In between those plates,
short waves, x-rays et cetera, are very happy. But long waves are not
so happy because they’re canceled out at the boundary by
the two good conducting plates. Therefore, this space in
here, between my hands, which is much magnified,
has all the energy states that are of high energy, where
the troubles are, and so has the space outside. But between the plates, the
low energy part is gone. Therefore, there’s a little
less fluctuation energy in the vacuum inside, which
is the truncated vacuum, than in the vast vacuum outside. And the plates
duly come together. And that calculation leads
exactly to the observed amount, without any
reference, of course, to the nature of electrons, or
the way the plates are made, or anything of that sort. The assumption alone is
enough that they’ll conduct. They shield the
electromagnetic field. Of course, they can’t
shield the very high energy that goes right through. So you don’t expect any
troubles from the infinite parts [INAUDIBLE] cancelling. But it would not play any role. This effect, called
the Casimir energy is somewhat puzzling,
I think, to everyone. We’d like to do without it. I know Professor [INAUDIBLE]
spent the last few summers here in conversation
often about this topic. He once said to me that he
felt that his mission in life was to keep the vacuum clean. But that in 40 years,
he utterly failed. And he still believed
the real, proper vacuum was empty and clean. But he’d be darned to see
how you’d demonstrate it. And in fact, it’s always
the other way around. The demonstrations
come out the other way. Well, that’s as may be. But you see there’s
one other element which comes in here, which is related
to the famous expression, e equals mc squared. I guess we could say, m
equals e over c squared. Because since 1915 or
so, we’ve recognized the most important
property of energy, perhaps, certainly
for an astronomer, is that it has not only
the usual properties. But it also has weight. It has gravitational mass. And this gravitational
mass can then be observed gravitationally. There is no longer the argument
that the zero point of energy is arbitrary. Because you can only
observe changes in energy from classical energy, or from
the dynamic point of view. You can now observe,
not the energy directly, but its mass by watching
them be watching the mass pull your test mass towards
it, ever so willingly. That’s what you’ve got to do. Nobody can quite do that. But in principle, that
should be possible. And so that puts the
zero point energy, the energy in the empty
vacuum, at a very strange way, where you say it
might show up somehow, if we can do
gravitational experiments. Now, of course, we
live in universe where gravitational experiments
are the whole thing. It’s only that we human
beings, on a tiny scale, cannot manage anything
with gravitation. Tension We can only fight
gravity and build up puny little things that
go a thousand feet up, or airplanes, or
rockets, or whatnot. But gravity, no, no, you don’t
suppose planetary gravities and turn them on and
off in a laboratory. It’d be nice to do that. But we can’t do it. But in nature, the
large scale universe operates by
gravitational forces. I have more to say
about that next time. But I’ll just assert
that at the moment. I think you’d probably agree. And these gravitational
forces suggest that, if there is a lot
of energy lying around in the vacuum, or
something like it, we might be able to
see it by studying, not in the laboratory,
but in the universe. This point was made forcefully
and formally, correctly, first, only about 10 or 15 years ago,
by academician Zel’dovich, who pointed out that the term
introduced by Einstein for a false reason, which
Einstein said he always regretted all his life,
when he first made the first cosmological theories in
1918, that term Constantine introduced then to make
the universe static, which we thought was needed. But we know is not
the case anymore. So we don’t need it. Nevertheless, he introduced it. That term is exactly what you
get from the constant tensor put into the vacuum. The stress energy tensity
of the vacuum benefited the study of the
subject, simply to say the mathematical
formalism of that theory naturally leads to using
energy in the vacuum. It is an ordinary
kind of energy. Because it has this
fluctuating quality. But it comes out just the same. And it’s the same
to all observers. It doesn’t show any difference,
whether you move rapidly or slowly through space. So it satisfies the Einstein
conditions perfectly. That was very striking. And everyone felt that that
was an interesting idea. But by and large–
and I’ve taught the course called cosmology for
quite a few years around here. And in the beginning, I always
said this was a silly idea. Why invent a whole
new complicated thing. And it was zero,
which isn’t there. We don’t see it and
don’t worry about it. And that was the
general point of view. And it has come back,
indeed, to astonish us. And I think this is where the
aether has reentered the world. Let me go a little farther. I think the next slide might
be worthwhile at this point, just to give you the theater
in which all this happened. I simply show two very
handsome galaxies. I want to remind you
we’re looking out through our own galaxy
into the distant universe, through the
foreground of stars– all these things are just
stars, mostly too faint to see, but perfectly acceptable
to the big telescopes and photographic plates. And here we see two
very well-known, rather nearby galaxies,
quite beautiful, which have a lot of
history of their own. And I shall take them
up the next time. In fact, I chose these two so
you’d get familiar with them. This is obviously a
beautiful spiral galaxy. Well, this is kind of
a spiral galaxy, too and you see it edge on. That’s the way it
is in astronomy. And no physicist will
ever take a picture of the most valuable piece
of laboratory apparatus through a foreground
that confuses everybody, and against the background
that he can’t control. I mean, that’s just
not the way to do it. But that’s what the astronomers
do all the time, unfortunately. So we’d like to have
a nice, clean picture. But we can’t and tell the truth. So this is the way it looks. Now, the next one, please. To show you that
not everything is what you see in the
handsome photograph, I’ve taken another picture
I want to use next time. Forget that this is a singular
looking galaxy, which you haven’t seen many like before. But look, the same
object is here and here. You may see the little ring
sticking out at the edge. A distant galaxy,
rather interesting for its funny shape. That’s not why we discuss it. I’m using it only to
demonstrate that we know only what we can see,
or, more precisely, what we can demonstrate
instrumentally, or in some way. And here, we see a lot of
light around that galaxy, that appears when you do the
singular thing of just exposing deeply, for a long time,
a long-time exposure, and using the right
photographic plates. You bring out much more
on the right-hand plate than on the left-hand plate. That’s just as real
as what’s inside. I don’t say quantitatively
how much it is. Because of course,
it’s all blackened. The brighter parts
don’t become– ah, perhaps I should mention that. Remember, in this picture,
it’s the astronomers trick. Instead of making a
positive from the negative, it’s satisfied
with the negative, instead of going
through many stages. And the negative is a
little easier to understand. So starlight is black. And black sky is white. [INAUDIBLE] And here
you see this mess. That’s a lot of stars out
there that just don’t show. And the fact that they hang
so close to this object means they’re not part of our
galaxy, but part of the object out there. And of course, many other
instruments, radio, telescopes, and the like, will demonstrate
similar lost material. Next slide, please. Fine, so we see we
have to look around to find out what’s out there. The most obvious
observation does not give you all the answers. It gives you some answers. Here is the famous
object, class of objects. It is called the Virgo cluster. It’s the nearest large,
large cluster, in which these are hundreds of galaxies. All these big spotty things
that are not beautifully round are galaxies. The image is so small that not
even many of the foreground stars show up on it. Because we’re looking out
through a galactic pole. But the star density is not
very high in our own galaxy. Fortunately, the cluster
was put out there. it’s really the
other way around. Fortunately, we
were made out here. Because we’re probably falling
into that cluster at some rate at the present time. In any case, this is one
of the nearest big clusters of galaxies. It has galaxies of all kinds
and sorts in it, which I’m not going to try to make much of. It as not only the spiral
galaxy, which we showed, which can be flattened edges,
or looking like spirals, or having spindle shaped
things all over this diagram. But it also has
objects like this, which is a round object, which
shows up in the next picture. So here’s the next
picture, very beautiful. A great deal can be
said about this picture. It’s something as big
as our own Milky Way, just in this picture. It’s spherical, not
flattened at all. It has, for the
benefit of those who can see it well, globular
clusters in plenty around it. It’s really, very, very nice. So what we can do then,
if we ask ourselves what’s out there in the universe,
we take our pictures, the best expose we can. We ask the radio people
to do the best they can, the infrared people, and so on. And we add it all together. Because we know
how much starlight comes out of a
given mass of sun. We know how much light comes
from dust, IR, and so on. And we do our best to
make a census of this kind to give a census of the
mass of the universe. Recognize this census surely
can err in at least one way. It does not very
likely get it all. So there must be a little
more mass, at least, than what you see. Because by building a better
photographic plate, or a better cryogenic mousetrap, or
something, you’ll see more. And therefore, you
know that you’re getting less than you can see. But you hope that you’ve
got, the biggest part of it. Otherwise, why all these PhDs,
and so on, that they give us. But of course, you can
recognize from the irony that that isn’t the case at all. What we find is that, if
we look more carefully, we’re seeing pitifully
little of the material that must be there. We should demonstrate it
in this very simple case. It is not a fair case. It is of the largest galaxies. It is central to the largest
cluster in the neighborhood. So I don’t claim that it’s
representative of everything. That isn’t my point. My point is to show how easy
it is to convince yourself there is much more present, and
then simply say by assertion, we find that in
many, many cases, not just in this wonderfully
measured example, which is, perhaps, the best example. Next slide, please. Remember that big
white spot you just saw was the same little
black thing that was up in the center
picture there, when I showed the many clusters,
many galaxies in the cluster. And here’s the same object,
only treated to a fancy plate, with a thing called
a densitometer, a computing-like
device, which measures how black the plate is, and
gives you a number for it, and then plots that number
in the form of a map. When the numbers are high,
it makes a white stripe. And when they get low,
it doesn’t do anything for a while, then
makes a white stripe when they’re one half as
bright, and so on and so on. And so it converts the
plate into a contour map of brightness by a machine. And of course, if the plate
has something that the eye can’t catch , like a little
margin to the galaxy, where there’s still light,
but it’s not enough contrast for you to see, this
object will display it. And so you see, in
fact, around M87– so that’s what this thing is– there is this series
of lines, contours, showing that there is a
skirt, or halo, of starlight, extending quite far out. In fact, this
circle there is just the size of the
whole thing that you saw in the previous picture. So lo and behold, the
thing has now gotten two or three times
bigger in diameter. Now, that’s not a
great amount, right? Because suppose it
were all uniform, that would only be say two or
three times cubed more volume. That’s only 10 or
20 times the volume. That’s a big error, but,
in astronomy, not too bad. Moreover, it’s far from uniform. We must admit that the center
is very bright, plenty of stars. And the outside is very
unbright, not many stars. So probably, we’ve
overestimated the error. Pretty good, we’re
picking up and getting some of this material,
depending on a good census. So the next slide shows a still
more modern and wonderful way of making a
measurement of the gas. Now, of course, you
see that I’ve already done what astronomers
love to do today. And that is make art
in the form of maps. Don’t think this is what
anybody can see by looking through any kind of instrument. But it is what an instrument
sees, mapped quite beautifully with a certain school
of New York style, in the following way. The white spot at the middle
is that same old visible M87, maybe a little bigger in
this case than the one you saw before. But it’s the same old one. But around it, that red
stuff, which is in contours, again, you see it, but
not such fancy contours turning black and white. Now, these contours are all made
bright red, and a little less bright red, and a
little less bright red. And you can follow
them as they go to the outside of the picture. Those map the intensity
of the light seen in the outside of that galaxy. But it’s not the ordinary
light of the eye. It’s the light of
the X-ray telescope. This was made on the
famous Einstein satellite. And it’s an analysis
by Gordon Stein and his colleagues at Harvard. It’s a very beautiful
piece of work. So you’ve noticed though that
this is now a great big sphere. And it’s all shining in x-rays. And again, something
quite remarkable can be said about it. It looks quite uniform. It is really round. It is just about as round and
uniform as the object inside. Of course, it’s tapering
away as you go out. That’s fine. But it’s radially symmetrical. So it looks as though
it’s not a violent thing. And this argument has
been pursued quite far. It isn’t throwing something
out or bringing something in. It’s matter that has gathered
there, and is staying there, and is shining in x-rays. That’s pretty,
generally, concluded. If that is true, can we measure
what’s keeping it there? Because this gas has a pressure. And that pressure
must be opposed by gas on the top of it holding it in. And that gas on the
top of it is held in by nothing but the
gravitational force of the whole system pulling
it together, exactly as the sun is held together. So this is kind of an x-ray
sun, but on a prodigious scale. This thing that you see it
400,000 light years in radius. It’s a very large ball. And we can measure
at every point the temperature of the
gas that makes the x-rays. It fits the argument
that it is a temperature. The temperature is pretty
similar all the way out. You can measure the density
of the x-ray producing gas from the intensity. That’s a direct piece
of atomic physics. So we know the density
and temperature of the gas at every point. Thus, we know the
pressure at every point. Thus, we know the
rung of pressure. Thus, we know how much force
is holding the inner layers in. And thus, we can calculate
how much gas is in the galaxy. And the mass is
pretty impressive. It is more than 100 times,
maybe 150 times the mass that you would have
assumed for it, if you just took the starlight
that you couldn’t see, even extending the starlight
with the tricks that we tried. There’s a lot of mass out
there that we don’t know. This was not the mass
of the x-ray gas. The mass of that
x-ray gas is only a few percent of this total. The x-ray gas is only a
decoration, only a marker, to show us that there’s
something there that exerts gravitational force. And we believe it to be– well, I’ll give some
reasons presently. But it’s clearly concentrated
toward the center of M87. And it goes out
into the outside. And this is quite
a general feature. in order to show this a
little more generally, let me go ahead for a moment. Here’s a spiral galaxy, a
not at all extraordinary one. There’s the top. There’s the spectroscope slit. Here’s a spectrum. Notice the jiggle in it. That’s put into a curve. What we are doing
is we’re looking at a galaxy that is edge on. Such a galaxy has to turn,
like a phonograph record, if nothing is still. And as it turns, this one
side is coming towards you. And the other side is
going away from you. The astronomer can measure those
speeds by the famous Doppler shift, in terms of the
speed of light, which he’s done and plotted there. Actually, she has done
and plotted there. This is a slide
from [INAUDIBLE]. And this is what you get. Now, once you know the speed
of circulation of a planet, you can calculate its
distance from the sun in our solar system, by
what is called Kepler’s Law. That is a very well-mannered
application of gravitation. And if you do this for the
galaxy, you do the same thing, it’s not quite so simple. And you’ll see why
in the next slide. Here are a few of them, 50
more like them, 30 more. Notice the velocity which
is plotted vertically against the distance, which
is plotted horizontally, has a lot of wiggles and so on. But it’s pretty flat all the
way out into the outskirts. But you don’t see
anything there. Very few stars can be seen
in the outskirts, just barely enough to get
your spectral lines. And the curve is not showing
any sign of going down at all. Therefore, the judgment
is extremely easy to make that here there’s a
lot of mass that you don’t see, that’s not shown in our
starlight pictures, that is holding the galaxies in the
orbits as directly measured by their speed. And that is quite a
remarkable result. Now, so people have added
that up rather generously. They can do it not only
for individual galaxies, but for clusters of galaxies,
for the motions among clusters. And every effort to
measure this mass comes out with the same result.
There’s 10 or 20 times as much as we see in starlight. Maybe that’s the conclusion. But then, there’s
another argument that makes that
conclusion even erroneous. So let me proceed to the
last of these slides. And then, I’ll talk
about it just a little. This is a version the famous
redshift curve, showing, in this case,
standard candles being explosive stars
in many galaxies, plotted the brightness
in some units. This is the brightness. And this is the
speed of recession. These are moving far
away and are quite faint. I’m sorry, these are far
away, and hence quite faint. These are close, I believe,
hence rather bright. And the shape of the
curve is something that can well be calculated. And the argument that is
the most striking argument in the last five years, which
I think many people have heard of in the headlines, at
least, is the argument that the cosmological
regularities we see suggest that we
live in a universe, which was inflationary. What does that mean? It means, simply,
that the universe– the scale on which
the universe exists, which was formed very long
ago before we were around to observe , is an
enormously large scale, compared with the one we see,
the time scale we measure, and the galaxies we see. These galaxies are only maybe 3%
of the time scale that we know. That’s a very small
part of the final curve, which we’ll someday have. That’s only a little tiny bit. Therefore, it
looks too straight. But the remarkable
conclusion, which has supporting other
points as well, and I want to try
to save some time, is the fact that this curve
is so nearly straight. Because a priori,
there is no reason to believe that it should not
be strongly curved, either one way or the other way. And the fact that
it is so straight has always been a puzzle. Well, somehow, it
was made that way.

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