In the last
part, we got to know about the astounding science behind the wormhole. But
that’s not all, Interstellar’s greatest spectacle is its blackhole and the
accretion disk surrounding it. A major plot point of the movie is the time
dilation effect experienced near the blackhole. Kip Thorne, Caltech physicist
and theorist, as well as the scientific advisor for Interstellar told them
straight off the bat, that to accomplish such a time dilation effect
realistically on a massive scale, they would need a humongous blackhole, or as
properly termed in astrophysics, a supermassive blackhole. This kind of
supermassive blackholes are generally
found in the center of galaxies, and keep the galaxies rotating. To show such a
massive blackhole with extreme mathematical accuracy and its gigantic size when
being shown against the tiny human spaceship was real hard work and to portray
it realistically, 3D was written off.
The
blackhole that was generated using Thorne’s calculation was extremely big, and
if compared in size to our solar system, the body itself would extend up to
earth’s orbit and its accretion disks beyond the orbit of mars. This was named
Gargantua in the movie.
This
blackhole, Gargantua’s mass is 100 million times of that of the sun. It is 10
billion light years away from earth and rotates at an astounding 99.6 % of the
speed of light.
We already
know how a singularity is created. In case of Gargantua its mass and speed of
rotation create an extremely strong gravity field, which bends the space time
fabric beyond the event horizon, and pulls light and time from beyond the
ascension of the singularity in the bulk. Einstein termed this as the time
dilation effect experienced around a blackhole. This means, if you were close
to a blackhole, then our perceptions of time and space would diverge. Relatively
speaking, time would seem to be going faster for me. This is in accordance with
relativity, according to which time passes slowly in high gravity fields.
In
Interstellar, the planet they visit exists at a distance from the event horizon
that 1 hour on the planet they visit is equal to 7 years on Earth. Graphically
this dilation can be shown as shown in the following figure.
Another
problem they faced during the making of the film was the scientific
plausibility of the survivability of the planets orbiting close to Gargantua.
Now, it seems that no planet can endure the extremely high gravitational field
resulting from the blackhole, which is the reason for time dilation. However,
it turned out that it in fact is possible but the condition is that the
blackhole needs to be spinning very fast, fast enough that the any other object
in circular orbit around Garagantua be spared the destructive effect of such a
high gravitational field. Hence Garagantua rotates at 99.6 % of the speed of
light.
In addition
to this, the accretion disk of the blackhole also posed a problem. Accretion
disks are ring like circular disks made of gases that flow into the blackhole
and are comparable to rings present around Saturn. The problem with the
accretion disks is that they are very energetic and emit a lot of fatal x-rays
and gamma rays which should have fried the astronauts alive as soon as they
reached anywhere near a blackhole of Gargantua’s size. But this was rectified
by placing the blackhole in such a phase where its accretion disk is in an
anemic state and is cooling down with its temperature at the time of visit similar
to temperature of the surface of sun. This doesn’t emit the x-rays and gamma
rays a normal energetic accretion disk would, thus not killing the astronauts
as well as making life possible on the planets orbiting the blackhole. Now, of
course such a cooled down state of an accretion disk has never been discovered
but that is due to the lack of sensitive technology for far out space
exploration, as the existing technology can only read high energy outputs and
such cooled down states are invisible to it. In fact, Igor Novikov, a Russian
scientist had worked out the relativistic theory of thin accretion disks back
in 1970.
After making
the existence of Gargantua in the movie as scientifically accurate as it was
possible, the team faced the problem of creating the phenomenon on screen. For
the wormhole, they had designed a new renderer which could treat light’s path
curved rather than just straight, and had successfully gotten a wormhole out of
it. So, they decided to use the same method for the blackhole. But blackholes
as suggested by the name are a murder of light, such that light coming from a
source wouldn’t keep travelling to infinity as is the property of rays, but
dies within the black hole. This caused an Einstein-ian effect called
gravitational lensing in the renderer due to which the bendy bits of
distortion, i.e., wherever the light bent and wasn’t travelling in a straight
line, overtaxed the computation such that some of the individual frames each
took up to 100 hours to render. In the end the movie brushed up against 800
terabytes of data.
But the
movie was in 2D, and after all this innovative imagery used in making of the
blackhole, it would have ended up looking like a flat 2D disk in the 2D visual
medium, despite its existence as a fully sized 3D render. Chris handed the task
of making the blackhole look like a 3D sphere, rather than a flat disk to the
head of the CGI team of Interstellar, Paul Franklin. He picked up the idea of
using an accretion disk found around some blackholes to define its sphere. This
accretion disk would later become a major plot point in the story as we all
know.
Franklin had
Von Tunzelmann attempt a tricky demo to try out how the blackhole looked like
with an accretion disk. She generated a flat, multicolored ring- a stand-in for
the accretion disk—and positioned it around their spinning black hole. This
resulted in something unprecedented and extremely amazing. The space warping
around the blackhole also warped the accretion disk. So instead of looking like
Saturn’s ring, the light created an extraordinary halo around the blackhole.
The Double
Negative team (the company working the CGI of Interstellar) thought of it as a
bug until it was shown to Thorne. It lead to a moment of discovery where Thorne
realized that the team had correctly modeled a phenomenon inherent in the math
he’d supplied.
No one knew
how would a blackhole looks like until they built one. Light, temporarily
trapped around the blackhole, produced an unexpected complex fingerprint pattern
near the black hole’s shadow, And the glowing accretion disk appeared above the
black hole, below the blackhole, and in front of it. Thorne had never expected
it, but later he realized that the phenomenon had been there in the math
forever, just waiting to be unlocked. In the end Nolan got his visually
immersive movie, Thorne got his wish of making a movie that taught its audience
some accurate science and both of them got something they never expected, a
scientific discovery. That’s why the appearance of the blackhole in the movie
is visually so complex, because it’s accurate.
It’s no
doubt that Interstellar came around together beautifully; the merger of real
science and stunning visuals have transformed this movie into a science fiction
classic, where the science is barely fictional but yet so beyond our reach that
it can be realized right now only in fiction but might be tapped into in the
future. Thorne also hoped that this movie might act as a bait for the viewers
as some of them might be attracted towards the field of astrophysics and
consider a career in it rather than become a lawyer, a doctor and other
professional jobs. In writing this article, I resound the same feeling as
Thorne that after reading this I hope someone starts taking the field of
astrophysics seriously as their future, which is right now the field of physics
with the most possibilities, with so less known and so much still to discover.
And who knows? In some dystopian future, this might just save us.
