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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.
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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.
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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?"