This episode is supported
by The Great Courses Plus. Telescopes have come a long
way since Galileo first fixed two lenses to a tube and
discovered the moons of Jupiter and the phases of Venus. But the telescopes of tomorrow
will continue this advance and allow us to crack
open some of the greatest mysteries of the universe. [MUSIC PLAYING] The Hubble Space Telescope is
the most important observatory ever built. Its stunning
images and spectra have opened up incredible
windows on our universe. But Hubble was launched
in 1990 and is still working hard over a decade past
its original 15-year designed life. It's time for the
next generation of great observatories. First up, is the Hubble Space
Telescope's much publicized successor, the James
Webb Space Telescope. With a diameter of 6.5 meters,
compared to Hubble's 2.4, it has over five times
Hubble's collecting area. That means vastly
greater sensitivity. As the largest telescope
ever scheduled for launch, the only way to fit
it into the rocket is to fold it, origami-style. Webb will begin unfolding
its 18 hexagonal mirrors on its journey to the sun-earth
system's second Lagrange point about a million miles away. It'll continue
unfolding, cooling, and testing for
another five months before opening its
cameras to the sky. These cameras see mostly at
infrared wavelengths of light, unlike Hubble's,
which are optimized for visible and
ultraviolet light. Why infrared? Baby pictures-- lots
of them, deep in debris and deep in the past. So planets form
around young stars. And young stars lie tucked away
in blankets of gas and dust. Longer wavelengths of
light scatter less easily than shorter
wavelengths, and so have an easier time escaping these
dust-packed stellar nurseries. Compare two shots from Hubble-- this taken in visible
wavelengths, this in infrared. Webb will see even longer
wavelength infrared light and so will bore even deeper. Webb's larger mirror allows to
detect objects 16 times fainter than Hubble. This will provide another
set of baby pictures, the formation of
the very first stars and galaxies in our universe. For these, Webb's sensitivity
and infrared capability are both critical. Light from these
earliest of galaxies has been traveling through
our expanding universe since near the
beginning of time. That light has been stretched
out by that expansion deep into the infrared. Webb may detect
objects at a cosmic age of just 100 million years,
far earlier than currently possible. Webb will help us
learn whether stars form galaxies or
galaxies form stars and the role of dark matter
in the whole process. Using infrared light is
a double-edged sword, because light has a dual nature. It can scatter off a dust
grain, like a particle. But it can also be deflected
by the edges of our telescope, like a wave, in a process
called diffraction. As a result, there's an absolute
limit in how sharply light can be focused. A single point, like
a star, will always be a little bit blurred
when it reaches our camera. The finest detail any
telescope can observe is given by the
diffraction limit, which increases with wavelength. This means that infrared
has a disadvantage over visible or
ultraviolet light. However, the diffraction
limit gets smaller with increasing aperture size. What Webb loses, due to
concentrating on the infrared, it makes up through sheer size. Its infrared pics
will be just as clear as Hubble's visible
light images. The biggest challenge in
observing infrared wavelengths is heat. Space is good for that, because
the heat glow of the atmosphere is so bright. But uncool telescope
electronics are even brighter. Webb's detectors will be
cooled with cryogenics to a frigid 50 Kelvin or
minus 223 degrees Celsius. It also sports a
5-layer sun-shield to block as much
sunlight as possible. This fragile structure
has the added benefit of blocking small space debris. Webb will pick up
Hubble's legacy. But without sensitivity
to visible or ultraviolet wavelengths, it will
not replace Hubble. The true successors to Hubble
will not be in space at all. A new generation of ground-based
extremely large telescopes is being planned. The first will be the Giant
Magellan Telescope, currently under construction
in the Atacama Desert region of the Chilean Andes. GMT comprises seven
enormous monolithic mirrors, each weighing about 15 tons. Together, they provide
an effective aperture, 24.5 meters in diameter, and a
collecting area over 80 times Hubble's and nearly
15 times Webb's. However, using telescopes
within the Earth's atmosphere comes with complications. Observing in infrared
wavelengths is hard. But GMT is built to explore
visible wavelengths, just like Hubble. Then there's the issue
of astronomical seeing. Though the supremely dry
air about the Atacama Desert gives us some of the best
astronomical observing in the world, even that
air is in constant motion. We can think of light from
a very distant point-like object-- say a star-- as reaching us
as a series of wavefronts. Our eyes and our telescopes
can focus those wavefronts back into a point. With perfect focus,
we can reconstruct every point on the sky,
creating a perfect image. But turbulence in the atmosphere
warps those wavefronts. To our eyes, this is what
causes stars to twinkle. For telescopes, it blurs the
crisp diffraction-limited images seen in space. This seeing, or size of
the blurring, increases. If we build GMT's
giant mirror in space, it would produce images 10
times sharper than Hubble's. But on the ground, that
resolution is normally limited to about 10 times
worse than Hubble's. But these days,
the most advanced ground-based
telescopes can actually correct for atmospheric
blurring with a technique called "adaptive optics." GMT's depth of optics
will be next-level. Its secondary mirrors will
be flexible, deformable at high speed by thousands of
computer-controlled actuators to correct the
warped wavefronts. In order to track this
turbulence in real time, GMT will shine six
powerful sodium lasers 90 kilometers into
the upper atmosphere, where their light will produce
artificial guide stars. Its mirrors will deform up to
hundreds of times per second to keep the guide stars,
along with everything else in the telescope's
sights, in sharp focus. With this technology,
GMT will be able to get close to the
diffraction-limited resolution promised by its
enormous aperture. GMT's extreme sensitivity
and unprecedented sharpness will actually allow
to take photographs of planets in
other solar systems and even to observe the
spectra of the atmospheres of some planets. It's hoped that GMT
will even find traces of the very first
population of stars that formed in our universe. Also in Chile will be
a new type of telescope we have never seen before. The Large Synoptic Survey
Telescope's primary mirror spans 8.4 meters-- 3 and 1/2 times
larger than Hubble's. But LSST's secret lies
not so much in size as its incredible speed. LSST will scan the whole
southern sky every few nights. This is possible because
of the giant field of view of its car-sized
3.2 gigapixel camera. In a way, LSST focuses more
on the dimension of time rather than space. It will see how
things in our universe move and change over
days, months, and years. By comparison, the
Sloan Digital Sky Survey maps large fractions of the
sky over an entire year. LSST is hundreds
of times faster. Every night for
10 years, it will take 1,000 pairs of exposures
and store 15 terabytes of data. We'll be able to
track the motion of rogue high-velocity stars
whizzing through our galaxy. We'll spot countless
fast-moving objects in our own solar
system, including potentially hazardous
asteroids that could one day impact the Earth. It will be easier to
find new supernovae, the explosive deaths of stars
which, among other things, will improve our
understanding of dark energy. We'll also catch the
visible light counterparts to gamma ray bursts, the
most energetic explosions in the universe or record
the twinkling of objects in the distant universe as
their brightnesses fluctuate due to the changing
gravitational effect of nearby massive bodies. This will allow us to map the
universe using gravity itself as a lens. Webb, GMT, and LSST will
change the way we do astronomy. They are designed to
tackle some of the biggest questions about our universe-- known unknowns. However, it's likely that
their most exciting revelations will be things we didn't
even expect to find-- unknown unknowns in the
deepest reaches of space time. Thanks to The Great Courses Plus
for sponsoring this episode. The Great Courses Plus is
a digital learning service that allows you to learn about a
range of topics from Ivy League professors and other educators
from around the world. Go t thegreatcoursesp
lus.com/spacetime and get access to a library of different
video lectures about science, math, history, literature, or
even how to cook, play chess, or become a photographer. New subjects, lectures,
and professors are added every month. Alex Filippenko's course,
"Understanding the Universe," is a pretty incredible survey
of pretty much the entire field of astronomy. It includes a great
lecture on telescopes, taking you from their
most basic workings to the big bad machines we
use in modern astronomy. With The Great
Courses Plus you can watch as many different
lectures as you want, anytime, anywhere,
without tests or exams. Help support the series and
start your one-month trial by clicking on the link in
the description or going to thegreatcoursesp
lus.com/spacetime. As always, thanks
to all our patron contributors for making
all of this possible. And a specialty thank
you to Jelle Slaets, who's supporting us
at the Quasar Level. Jelle, with your
help, we may even be around long enough to
show you the first images from these telescopes. So last time, I
showed you how you can visualize the effects
of special relativity on spacetime using geometry. The resulting shape
illustrates the direction of the flow of causality. It caused some stirs. For example, a few
of you noted that I murdered the pronunciation
of Minkowski's name. Normally, I just
claim that that's how we say it in
Australia, but I don't think that will fly this time. Sorry, Minkowski fanboys. A few of you wondered
about the relationship between the geometry I depicted
on the space-time diagram and the geometry that comes from
mass and energy-curving space. Let me reiterate. The space-time diagram I showed
is for flat or Minkowski space. There's no mass or
energy warping it. It's flat. The hyperbolic
geometry is just what you did when you map
the space-time interval to a third dimension. So you have time, space,
and space-time interval. Then, you see this downhill
direction of causality. It's not really downhill. But the representation is really
interesting to think about. By the way, a lot of people
express the space-time interval with a minus sign in
front of the delta X and a plus for the delta
T. That's just a convention and just as valid. In that case, your
causal future is uphill rather than downhill,
which sounds exhausting. QED asks, if he gave
me a black hole, what would be my first experiments? Well, I would start a
YouTube channel called "Will it Spaghettify?"
