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impact theory enjoy the episode
hey everybody welcome to another episode
of conversations with tom i am joined
today by somebody that i've been waiting
30 plus years to speak to the
legendary astronomer alex filippanko
alex thank you so much for joining me
well tom it's my pleasure and my honor
you know you've done so much to impact
people's lives
in a positive way you know i've watched
a number of your programs it's just been
fantastic
and you and i share a number of aspects
of our lives
in the for example we like to set goals
we like to be efficient
work hard be motivated know why it is
we're
motivated and so what you say to people
resonates very much with what i've
you know how i've conducted my life and
how i try to inspire people as well
wow man thank you for somebody who was
on
one of the teams i think there were 50
of you that essentially won the nobel
prize i know it can only go to three
people
um but that you were on that team that's
incredible man thank you you obviously
have
very useful goals so
very excited to to sit down and have
this chat and hopefully the next time we
do it we'll be in person
that would be amazing yeah i mean you
know weird circumstances but
i know that in the past year you've had
a lot of practice
doing these um you know skype interviews
with people and they worked out really
well it
it's almost as though i'm there with you
in person
yeah it is uh the technology is a saving
grace and when i think about
the fact that this wouldn't have been
possible if this had happened back in
you know 2010 like this wouldn't have
been
possible so i know there are a lot of
times when this could have
occurred and been just disastrous
even more so than it's been now so uh
for that i will i will certainly tip my
hat in gratitude so
uh yeah technology has brought us
together and here's something in fact
that a lot of people
may not understand about astronomy and i
was saying before we started rolling
that one of the things that um
i was once asked what i would be if i
wasn't an entrepreneur and i said an
astronomer and
admittedly that um is is accurate in
terms of how astronomy makes me feel i'm
way too bad at math to actually do it
um but there's something about the
the grandeur but the way that it's
usable and when i heard that
um the theory of relativity was
necessary for gps to work
that's when i was like wow there's a lot
of things that we have around us that we
take for granted that actually have to
do with physics and people looking up at
the stars
and i wanted to start with what you
teach in your basics of astronomy class
you say there's like four or five things
that you want people to learn
and if they don't learn you're going to
come back and fail them you know even if
it's 20 years deep in their career
what are what are those handful of
things yeah you know
one of them is that as carl sagan used
to say we are made of star stuff
and by that what he meant was that
the heavy elements in your body the
carbon in your cells the oxygen that you
breathe and that's in water
the calcium in your bones the iron in
your red blood cells the phosphorus in
your dna
all those heavy elements were cooked up
through nuclear reactions deep inside
stars
during the course of their normal
evolution and also when they explode
some stars explode
and this debris goes flying out and
mixes with other clouds of gas
gravitationally collapses forms new
stars they
then go through the same process of what
we call nucleosynthesis and then stellar
explosion etc etc
and after billions of years of evolution
our galaxy the milky way galaxy had
these clouds of gas that had a
sufficient quantity
of heavy elements that rocky earth-like
planets could form
and then somehow somewhere you know
bacteria formed little
singular cell organisms formed and
through billions of years of evolution
here we are
sentient beings that can come to
understand
the process of our origins the origins
of the very elements of which we are
made
if that doesn't grab you i don't know
what will
right that we're made out of atoms
that were literally spat out of
exploding stars
yeah that one's interesting to me for a
couple reasons one it gives you a sense
of
um this sort of star wars moment of a
long time ago in a galaxy far far away
that there were that we've sort of come
along so late
that stars formed and collapsed and
exploded populated you know other places
and then we ultimately come out of that
it really gave me a sense of like what
13 billion years really is
uh an extraordinary amount of time um
well the other thing
one gives it gives it a purpose to the
universe right if the universe had
only inanimate objects like rocks and
stars and things like
black holes it wouldn't be able to think
about itself
and reason through how it all came to be
and how it evolved
in a sense we are the way in which the
universe is found
to know itself and you know there may be
others i don't know but
we're the only ones the only sentient
beings with this capacity to ask and
answer
abstract questions and that's just a
marvelous thing
how do you contextualize that like is it
poetic for you
is it religious like how do you make
sense of that
yeah you know it's some combination of
poetic religious
spiritual for sure uh
you know we all try to find meaning in
our lives and there are many ways
one can find meaning but one way that
i've found
is to contribute in some small way
hopefully a large way but at least in
some small way
to humankind's understanding of the
cosmos
of this amazing and magnificent universe
in which we live
and one thing i try to do in my
semester-long course at berkeley
is to show students not only the
magnificence of the universe and its
contents
but that through this process of careful
thinking observation experiments
we can come to and have been coming
to a pretty good understanding of how it
all works
there are a lot of things we still don't
understand absolutely
new things continue to be found i mean
as a scientist it would get boring if
there weren't new unexplained things to
continually answer
that's why i'm in it but we also
understand
a lot as well and you know testament a
testament to that is the fact that we
can build
airplanes and rocket ships and
pacemakers
and and these electronic devices through
which we can
talk no matter where we are in the world
right
that's a testament to the success of
science
yeah it's it that
when so i'm not a religious person but
when i
think about the relationship between the
cosmos sort of how vast it is
and how much there still is to
understand and yet
through the things that we've discovered
so far how we're able to
shape the world around us i'm obsessed
with this idea that skills have utility
and there's another way to say it would
be
knowledge has utility insights have
utility and getting people to understand
you don't
read a book to check you know a box on
the list you don't go to college to
impress your parents
you don't even look at the stars just to
say that you can it's
you're getting data back from that and
that data then lets you do something and
one of the like you talk about wanting
to have an impact on people one of the
things i want
people to get is like when you learn
about something
you then can build a bridge
erect a building create gps travel to
the stars like
it that fills me with
wonder it feel fills me with a sense of
agency
and if you begin to tell yourself the
right story then it becomes also meaning
and purpose
and like that's the juice and it's so
crazy
like when you look at the stars what do
you
feel i i feel basically all the things
that i just said and i have such a hard
time putting it into words but what do
you feel when you
look up yeah no actually i think you
expressed it quite eloquently
you know i feel a oneness with the
universe
that i'm part of this grand structure
that
evolved over 13 or 14 billion years
and here i am a small subset as far as
we can
tell that that can strive to understand
it you know
and i don't have to be the one who makes
the discoveries you know i'm an
astrophysicist but
i gain joy in learning what biologists
have
have determined you know the the human
genome project
crispr cast nine all these advances that
can be
amazing for the benefit of humans but
also just
intellectually so provocative so
enthralling so ah inspiring right
that we are these creatures that can
come to this understanding
and you know going back to something you
said at the very beginning you know
general relativity
was this weird theory of warped space
and time that some crazy hair
you know theoretical physicist you know
albert einstein of course dreamed up
fast forward 50 years and even 100 years
actually
and here we have gps which with all of
its
military and commercial applications
that simply would not work
if you didn't take into account the
warping of the
passage of time depending on where you
are in a gravitational field
and an even better example is quantum
physics you know a century ago
physicists were thinking about the world
weren't interested in making a better
toaster
or or improving cars or whatever
there were two major questions
understanding the nature of light
and understanding the existence of atoms
and you might think well those are just
you know
intellectual titillation it doesn't
really matter but it does because fast
forward a century
and today's micro world the half a
billion
transistors at the head of a pin
basically right
moore's law all that that's built on an
understanding
of the quantum world the nano world you
know these
little seven nanometer pixels that are
now
infiltrating electronic devices and
storage units and stuff
that was all an unanticipated spinoff
of sort of blue sky wondering about
the world and our place in it and how it
works
so you know that's the best of both
worlds we satisfy our intellectual
curiosity
and we do things that are for the
benefit of humankind
yeah it's a great way to look at it um
as you were talking it made me remember
something i've heard you say in
interviews before
that as your wife knows every now and
then you sort of wake up in the middle
of the night screaming that we may know
nothing like
like there might be some huge revelation
coming
that will show that we're sort of as
both brilliant and ignorant as somebody
like newton right who couldn't have
conceived of what was to come and yet
gave us these tremendous breakthroughs
do you think
because when i i can sort of grasp
the big concepts of astronomy
but when it gets down to the to the
quantum realm
i start freaking out in like a really
fun way but like the double slit
experiment
in um in physics quantum physics
particle wave look at don't look at and
things change like
that freaks me out in a way that i love
so much
and in science you often talk sort of
the
the miracle the the axiomatic part you
get down to where it's like
you just have to trust that this thing
is real do you think there will ever be
a point where there's sort of no more
miracle to get to where we know like
what the vacuum is made of or
like i'm not even sure how to ask that
question
do we ever find the base it's a great
question tom it's something that
scientists and in particular physicists
struggle with all the time
the short answer is probably we'll never
have such a theory
and the reason is is that science and in
particular physics
is not so much after the truth with a
capital t
reality with an uppercase r but rather
a description a quantitative description
that allows us to
explain quantitatively the results of
experiments that have been done
and to make predictions about the likely
outcomes of experiments that have not
yet been done
to the degree that we can explain what's
been done and make predictions that then
get
verified we pat ourselves in the back
and we say we have a pretty good working
model
but we never know whether there will be
some experiment in the future
that does not conform with the
predictions or expectations of our model
of our description
in that case it'll have to be modified
sometimes in small ways
other times in fundamental ways like
einstein's
relativity which was a completely
different way of of looking at newtonian
mechanics
and then the quantum world you know that
that deals with the very small
and you have general relativity that
deals with the very large
if we someday have a quantum theory of
gravity that's
well verified and tested and explains
situations where there's a lot of mass
in a small volume we may pat ourselves
in the back and say hey this is working
we have the final theory but who's to
say that
some young whippersnapper someday won't
find an
experiment that doesn't agree with that
and so
a new modification will have to be made
so it's always a description
a model within the context of what our
brains of k
are capable of constructing it's unclear
whether this is the underlying reality
right
yeah that that question to me is um too
tantalizing
to leave alone and i'm not sure why i
find it so
interesting because certainly somebody
like myself is never
going to make use of that knowledge it's
just not what i've aimed myself at
um but there is something magical to
einstein's question of i want to know
god's thoughts and everything else is
just details
what do you think about that like i
think he had a comp well
as we look back on his life i think we
have a complicated relationship to what
he meant
by god um he may have had a very clear
relationship
but what do you think about a sentiment
like that do you find that equally
intriguing to you is that just
not worth pondering yeah uh
it's an interesting question because you
know there are books of
einsteinian quotes you know there's like
a thousand of them or something he's a
very quotable
person and there's a mark a remarkable
number of them in which he brings up god
and this has led many people to think
that he was a deeply religious
person in the classical sense it's not
true
it turns out that his god was what's
called spinosa's god
it's sort of the god that that is
nature that explains sort of you know
the ways in which the natural world
works it's sort of the god of the
natural world
he did not believe in the classical god
who's sort of
you know watching over things and maybe
even you know influencing them along the
way
so when he said he wants to know god's
secrets
i interpret that to mean that he wants
to know
really to the degree possible what are
the fundamental laws
quote unquote for laws because even he
admitted that
these are all just descriptions and
models
but nevertheless the farther down the
path you go
the more complete you think your
description or model
is because it explains and is consistent
with
more and more observed phenomena and so
we begin to think
of it as being the reality
even if deep in our hearts and of course
i didn't know einstein but
i speculate that deep in his heart he
probably would have admitted
that this isn't necessarily the reality
it's just a description that happens to
work really well
and for example in a quantum theory of
gravity
you don't even have curved space time
you have these little particles called
gravitons
that are zipping back and forth between
say earth
and the sun telling each other that
we're here and
for the earth to be gravitationally
attracted to the sun and same thing with
the moon
and the earth whereas in his theory he
thought of it
as being the consequence of a curved
space-time but that's just a description
or a model
that happens to lead to calculations
that can be done
relatively easily and whose outcomes can
be
compared with things like the orbit of
the moon
or earth okay but again it's just a
model it's just a description
and i think he understood that that's
all it is but was hoping that through
the
end of this process we will someday know
the final
theory even if he perhaps didn't think
that that was ever
really truly possible there's a lot of
interesting things around there so
um one the reason i said that i've been
waiting whatever 32 years for this
interview
is when i was a kid i was
just unable to wrap my head around the
idea of an expanding universe
which i know is one of your areas of
expertise because i just kept thinking
all right hold on
if you expand a city you expand it into
the areas that are forest or whatever
there was something there if you build a
house
there was land there before you built
the house what
is the universe expanding into even as
you get into gravitational waves right
like you imagine this thing going up and
down
what what's below it what was above it
like
i even now i'm like i don't understand
how what what are we expanding into
right
so here's where i like to use analogies
all right um
first to answer your question there are
two ways of answering it we aren't
necessarily expanding
into anything and i'll clarify that in a
minute
or you can think of it as expanding into
a fourth spatial dimension
so we have x y and z okay
this would be a fourth dimension that we
can't see
we can't touch we can't experience it's
mathematically describable but
physically
inaccessible okay can we before you move
on can we describe
what you mean by physically inaccessible
are you saying that hey we've got eyes
ears touched they
we have an umvelt we have confused that
umvelt with
all things and once you get beyond our
sensory perception
because that was one thing i struggled
with a lot until i
came to understand sort of david
eagleman's idea of
you're just a mr potato head and you
could read
magnetic signals but we don't have those
receptors
a shark you know can sense magnetic uh
or electrical
movements so you can actually trick a
shark i still can't believe this is true
but i've seen the footage
you can put a a plate on the floor of
the ocean that has an electrical current
that mimics the electrical current of a
flopping fish an injured fish
and the shark will just sit there
attacking the plate all day long
because it's actually picking up on the
electrical signals
that made me realize whoa like there is
a lot of data that we just
can't perceive and so because i know
what you're about to
explain uh is that what you mean by we
can't perceive it
it's it's beyond even that sort of
perception you know the shark thing
if we have the right sensors and
scientists have done this this is how
they know
they can detect those signals even
though with our eyes we cannot but
there's all kinds of for example
electromagnetic radiation light that our
eyes don't perceive
you know radio signals and x-rays and
stuff
what i'm talking about are actually
other dimensions
so here's where i like to use an analogy
and you know a piece of advice i give to
people to clarify your ideas with an
analogy when you can
so i'm gonna i've got this balloon here
all right i anticipated this question
tom
and so i'm gonna
suppose that this is a hypothetical
universe
where you're constrained to be on the
balloon
actually more technically within the
rubber itself
and you can only go forward and backward
left and right
and any combination of those two motions
okay
along the surface or or through the
balloon the laws of physics prevent you
light or anything else from going into
the balloon or
out okay by do you is there a known
mechanism by which we are stopped
well in this hypothetical universe no
i'm just asking you to suppose it so
in our universe the mechanism would be
that
all the particles light protons
electrons
are restricted to the usual xyz
dimensions in this room okay and we're
still trying to figure out why
in string theory the reason is because
every particle
is a vibrational mode of a little
package of energy called a string
and the ends of the string are tied
down they're anchored to this xyz
space okay but whatever the mechanism
you're restricted
in this case to only being within the
balloon
now the balloon can expand and i
forgot to bring my little stickers but
in my classes i put little stickers on
this
and the stickers move away from one
another and if you imagine a sticker is
a galaxy like our milky way
you would see the other galaxies moving
away
each of them thinks they're at the
center but none of them is in the unique
center
the unique center is the center of the
balloon right
but that's not part of the universe as
i've hypothetically
defined it the universe is only the
balloon
the center is in a mathematically
describable
but physically inaccessible dimension
and so too is the expansion
i blow some more not too much otherwise
i'll get a little bang
a little bit of nerd humor there but it
expands into this dimension
that we can describe very easily
mathematically okay
the r dimension in polar coordinates
but the dude in the
in the balloon does not experience
the r dimension outward or inward
they only say we are at r equals six
centimeters or whatever it is okay
they know about are extending farther
outward and inward at least
mathematically they know about that
but they can't actually go there or see
it or anything like that so in that
sense
now take our three-dimensional universe
think about a three-dimensional sphere
not the inside of the sphere but
something that wraps
around a fourth dimension we're
expanding
into that fourth mathematical dimension
even though we can't see it or even
conduct any experiments
unlike the shark case that show us that
it's there
okay does that clarify things a little
bit for you
that is extraordinarily transformative
in my life and i
actually mean that literally i now know
why you have won so many teaching awards
but now what you've done is simply give
me the next question to ask which is
extraordinarily powerful and what a gift
but now i'm going to ask it and let's
see where we go so
the part about string theory really
helped with the breakthrough
in that there's something that we don't
know yet
that there's some force i'm going to use
my
language and if i misspeak please stop
me but
there is some as of yet unknown force
that is anchoring us within the rubber
of the balloon and that's really
important for anybody who's not watching
to
to think about the universe being only
that layer of rubber and your entire
life
is within that layer of rubber and there
is a force
as yet unknown that keeps us in that
layer of rubber
make sure that we can only see within
that layer of rubber and even detect
only within that layer of rubber so now
my question is
what what is that like so the r
dimension
and this is using analogy so i look up
at the stars
i have this sense of wonder and awe and
it triggers in me and i don't know how
much you
um know about sort of the other side of
my life but actually right
and impact theory is meant to be a film
tv studio the whole nine
and i'm always drawn to science fiction
because it you get to play the
well what if it were like this game and
one of the
analogies that i find just absolutely
exhilarating is uh and i had somebody
tweet me
this question to ask you is in men in
black
at the very end of the first one they do
this pull out pull out pull
out pull out until you zoom out far
enough of our universe to realize that
we're really just
a marble in an alien universe and
everything that we think of as
is the universe in existence is you know
this actually really really small thing
and this idea of bubble universes
where were there some greater which
still doesn't answer the question of
what
but you know there's some greater thing
holding this
foam of bubbles in every bubble as a
universe
yeah that to me is i want that to be
true
so badly like there's just something
about the the
just it's so big and so unknown now
let me anchor sort of where i'm going i
read once
that gravity becomes where everybody in
the
physics and astronomy community pay
attention because it's the one sort of
mysterious force
and all the other ones make sense but
there's something about gravity's too
weak
if i'm not mistaken can you explain that
right so there's a lot to unpack there i
mean
right questions you know you should
clone yourself and become an
astrophysicist all right
i'd have to get a lot better at math so
first of all yeah
the idea of multiple universes has now
gained real respectability i mean
card-carrying
physicists astrophysicists are thinking
seriously about the possibility because
we could discuss this later on but ideas
about how our universe
was born and evolved with time naturally
lead to other
pockets that are essentially independent
of ours and so there could be
you know a gazillion of them there could
be an infinite number of them okay
so i'm you know i i like that idea a lot
for a lot of reasons
now getting back to your specific thing
about gravity
yeah if you look at the four fundamental
forces of nature
there's two nuclear forces that keep the
constituents of protons and neutrons
together and they keep
protons and neutrons together in a
nucleus that's called the
strong nuclear force then there's a
thing called the weak nuclear force
which sort of keeps the
neutron together in a sense then there's
electromagnetism which keeps the
electron and a proton
in a hydrogen atom together and then
there's gravity which keeps
us to the surface of earth when you look
at these four
forces in terms of their natural
strengths relative to one another
gravity is like 38
orders of magnitude 10 to the 38 power
weaker than these other ones which you
know they're not all exactly the same
but at least they're comparable to one
another
but gravity is like 38 orders of
magnitude weaker than electromagnetism
which is to say that the electron and a
proton in a hydrogen atom
feel essentially no gravitational force
they are
completely and utterly dominated by the
electromagnetic force
well a big question is why is gravity so
weak
and one idea is that although the
particles i described in string theory
are these little open-ended strings that
are tethered to the rubber that we just
talked about
the carriers of gravity these gravitons
are thought to be loops and they can
escape from this rubber balloon
and go floating off into that other
dimension which is called the bulk
bulk this is like a membrane
a brain in the bulk and there are other
membranes elsewhere
but if most of the gravitons are
floating around in the bulk
then there are not many of them in the
membrane
that is our universe that's one idea
of why gravity might be so weak and so
those those gravitons would actually be
having an impact in our membrane or no
um not really except that
the corollary of what i just said is
that gravitons from
other universes in this bubble theory
could
reach and get into our membrane and
that might be one way of testing
for the presence of these other
universes which at this point are
completely speculative
it's an interesting idea that seems to
fit well with a lot of our other ideas
but there's not a shred of direct
evidence
for these other universes but this
might be a way of finding that evidence
if
someone were to someday directly detect
gravitons
and find some way of figuring out
whether they came
from our piece of rubber or some other
piece of rumor
somewhere out there i don't know how you
would do that but it's within the realm
of speculation at least
is anybody asking the question around
whether we could ever
like us as a whole human being or even
with an instrument
but sort of rip through the membrane
and exit out into the i forget what you
just called it but that
other space the what the bulk a bulk
yeah so has anybody speculated can we
theoretically
cross into that region yeah um great
question
black holes which are regions of space
where matter is compressed so much
that nothing not even light can escape
okay
can be thought of as rips in the fabric
of space-time
because they end up with a singularity
either infinite density that is you know
a finite amount of matter in zero volume
or if you bring in quantum physics maybe
it's just a very very high density you
know but not infinite
but in any case it's definitely a
weirdness
in our otherwise smoothly varying space
time
and the equations even suggest that
on the other side of the black hole in
our universe
it opens up into another black hole in
one of these
other universes or in a very distant
part of our universe
and so if we could find well if this is
true this hypothesis
and if we could find a way to hold the
throat of the black hole open
so that we could safely pass through
there might be a way
of actually experiencing
that is getting into or at least getting
information from
these other universes again this is
highly speculative
but these would be essentially rips or
wormholes
in space that give us access to other
universes
very highly speculative now this is this
is the stuff i
i absolutely love so let's play with the
speculation for a minute so
um one there's a few things around this
i've always been super curious about
forgive me for
asking sort of rudimentary questions
what is it
about so you talked about the throat so
i know
there's um probably a gravitational
effect that as you cross the event
horizon would just rip you apart
because your your toes would be more
impacted by gravity than your head and
so you would just literally disintegrate
so i understand that
but um what then if we
talk about opening the throat are we
somehow stopping
that that gravitational um
discrepancy like what what do we mean by
holding it open
yeah okay so the effect you're
describing
uh of being ripped apart is
affectionately known by astrophysicists
as spaghettification because you get
stretched in the long direction and
squeezed in the
you know along your width uh
that actually happens for a relatively
low mass black hole
maybe 10 times the mass of our sun it
indeed
happens outside the boundary the
so-called
event horizon of the black hole and
you'd get ripped apart
but it turns out for gigantic black
holes a billion times the mass of our
sun
like the ones that exist yeah pardon
that exists yeah yeah you know um in
april of
2019 just two years ago the event
horizon telescope
team showed using
a bunch of radio telescopes on different
continents
they showed this amazing picture of a
black hole in another galaxy
actually the silhouette or the shadow of
a black hole since
no light comes out of a black hole you
can't actually get a picture of the
black hole
but this is the silhouette of a black
hole
and it's in a galaxy called m87
55 million light years away which means
it took
light you know 55 million years to reach
us
but that corroborated the evidence we
have
from other lines of reasoning and
measurement that these black holes
really do exist in the centers of
galaxies and our own milky way galaxy
has a black hole roughly four million
times the mass of the sun and that was
in fact that discovery
was recognized with the nobel prize in
physics just last year
in 2020 to two colleagues of mine
reinhard guenzel
here at berkeley and in germany and
andrea gaz a colleague of mine
at ucla her team and guenzel's team
showed really clear evidence that our
milky way galaxy has one of these
so-called supermassive black holes
so for the supermassive ones you
actually don't get ripped apart
just outside the event horizon the
boundary
you get ripped apart when you're closer
to the singularity to the middle
but regardless the worst ripping apart
and then squishing together occurs at
the center the singularity
so by holding the throat open i actually
mean
preventing the singularity from existing
and squishing you and along the way
preventing the
gravitational forces from first ripping
you apart
you got to do all those things you got
to be not ripped apart
and then not squeezed in to an
infinitesimal point almost
in the singularity so you need something
with a negative gravitational
effect like negative mass and that's
invoking the tooth fairy right now
because again maybe some day someone
will figure out a way to either find
this stuff
or make this stuff so it's not
completely
out of the realm of possibility and i
always like to be
you know forward thinking you know not
everything is possible but
some things that have not yet been
proven to be impossible
might be possible although very very
difficult you know
that is intriguing so uh the singularity
for people that don't know that
um when we get into the math because i
can give you a layperson's explanation
of it's the point beyond which we can no
longer predict what happens
but what is the mass saying that it's
infinitely dense
yeah so what's called classical general
relativity which doesn't
include quantum effects so it can't be
anywhere close to the final word okay
nevertheless you know classical physics
newtonian physics has served us well
general relativity through gps has
served us well blah blah blah
the classical prediction is that no
matter how much matter you throw into a
black hole
it all squeezes down to a mathematical
point
now a mathematical point has zero volume
r the radius is zero so r cubed
you know the volume is zero as well so
that means an
infinite density mass per unit volume
um so no matter what you throw in you'd
just squish to an infinite density
again none of us really believe that
because
all other times when we've thought about
nature
on sufficiently small scales we've had
to introduce quantum physics and so
it is thought that the next big thing
will be a quantum theory of gravity uh
and you know hawking made
steps in that direction he tried to
unify quantum physics and general
relativity
but even if we don't get squished to an
infinite density
no doubt will be squished to a very very
very very very high density
unless we find some sort of
anti-gravitating material
that can preclude the formation of the
singularity
and the associated deleterious effects
on our existence
that's amazing okay so i'm going to keep
asking ignorant questions because
i feel like i'm sort of making progress
in my layman's understanding here
uh okay so we're worried about getting
squished down way too small when i heard
you describe
that it it has infinite density
as a lay person it sounds like i may
have accidentally come to the same
conclusion that
that's sort of the only thing we can
rule out we know it can't be
infinite density is that what gives
birth to this idea of on the other side
of the black hole there has to be
something spitting things out
because otherwise it just seems like it
it
and again i just don't know anything
about this but it doesn't seem like
you could infinitely shove
every quantum particle down into
a something with zero radius right like
something
it seems like something has to happen
yeah yeah yeah
and you know by the way your your
questions are perfectly reasonable and
this is a very
abstract you know mind-bending topic
that a lot of people are interested in
and so i get the same kinds of very good
questions
over and over again so they're great
questions okay
so the idea of it spitting out the other
side or at least opening up into a black
hole the other side doesn't come
from the impossibility of infinite
density
yes we don't know how to get an infinite
density but let's just suppose you could
okay the mathematics still
opens up to another black hole and
it's just because can i stop you there
so because i didn't understand the first
time but i just let it go
so if it's opening up to another black
hole isn't that just something also
sucking things in yes
but from the perspective of something
that went in
on the other side it can come
out so if it is that hawking radiation
yeah well yeah um well that's related
i'll get to that in a second
if it goes into a black hole in our
universe
it can't come out of the same black hole
in our universe but it can come out
in a different universe it's called a
white hole in that case
okay do we have white holes in our
universe no we've never seen one and
this is why
a number of us think that this is just a
theoretical speculation
and that there are no real such objects
okay because you can't throw
you know keep the throat of the wormhole
open or whatever
the white holes would be very obvious
they would be things
that are squirting out lots of matter
they're very powerful they're very
obvious
they're not hard to find like a black
hole that
doesn't emit any light these things
would be super obvious and yet we've
never seen one
so but but at least theoretically it's a
possibility
that even stems when you have
the theory with an infinite density the
infinite density is okay
it's just that you have a mathematical
solution to the equations
that gives you another universe now
often in physics
we get solutions that
you know have a positive and a negative
sign
so let me give you an example suppose i
construct an experiment
with a pendulum or something that gives
me
the mass of an object a paper weight
and i tell you the the square of the
mass tom
is 100 square grams and then i ask you
what is the mass what would be your
answer if the
square of the mass is a hundred square
grams the mass is
a hundred squared if it's not that i
have no idea you have no idea how much
math is a black box to me so
so it's this you know 10 squared is 100
so the square root of 100 is 10 okay
perfect
so you'd say the mass is 10 grams if the
square of the mass
was 100 square grams okay
but an equally good solution is negative
10 grams okay uh
and by the way when you squared it that
was an easy mistake to make because the
way i phrased it i now see
it was ambiguous what i meant i promise
you it's not not your fault
this is a yes but what i meant really
was not to take the square of 100 but
take the square root so that was an easy
thing to make but
the point is is that the square root of
100 is either negative 10
or positive 10 grams
so we throw out the negative 10 gram
solution as being
unphysical right it's meaningless so the
mass of your paper weight was
10 grams not a very good paper
paperweight i should have taken a a
different example okay a little
ball bearing or something but we throw
that out as being
unphysical well you know who's to say
someday someone won't find something
with negative mass maybe they will
maybe they won't so in the case of black
holes
a solution to the equations is this
black hole or white hole in another
universe but we don't know whether
that's a physically meaningful
solution that nature actually chooses to
adopt
or whether it's just a mathematically um
possible but physically irrelevant
solution
like the negative 10 grams currently
seems to be
at least to me but again maybe someday
someone will find
what the negative 10 grams is you know
and there have been
examples of this in the history of
physics a physicist named paul dirac
about a century ago combined einstein's
special theory of relativity where the
speed of light is the maximum speed
with the fundamental equation of quantum
physics called the schrodinger equation
he came up with something called the
dirac equation the relativistic
schrodinger equation
and out popped a particle
that looked pretty much like an electron
which has a negative mass but it had a
positive mass
and at first he thought this was
unphysical but then he said well why
don't you know why don't you people look
for it experimental physicists and
they looked for it and sure enough there
it was
they found the neck the positive
electron it's called a positron
so um you know there have been cases in
physics
where the initially ridiculous looking
solution
or possible mathematical solution turned
out to be
something that corresponds to physical
reality but there have also been cases
where we've not found
a physical counterpart the white hole
being among the things we've never found
another example is particles that travel
faster than light
in special relativity that's not
impossible they're called
tachyons they're traveling always faster
than light
and to slow down to the speed of light
would take an infinite amount of energy
well physicists have been looking for
tachyons
for decades and they've never found them
maybe they don't exist
or maybe we just haven't found them yet
we we don't yet know
see so we're exploring all these
interesting mathematical solutions
to see if they correspond to physical
reality
does that help you out very much so and
so now i have a question tell me why
this is wrong
so as you're describing and obviously
i'm existing in the abstraction layer of
analogy but
as you're describing this white hole and
my
my um you know whatever just the way my
brain works the sort of leap it makes
when i think about
a black hole just sucking in all this
stuff all this stuff all this stuff all
the stuff
and you tell me that the math says that
there's sort of a black hole on the
other side of that but it would really
be this white hole
it makes me the leap my brain makes is
oh well on the other side
is a white hole is essentially the big
bang
so you cram on one side all this stuff
into a black hole cram cram cram cram
cram
and then it reaches some theoretical i
have no idea what
you know math it has to hit but it hits
some point
and now it has to eject and so what we
think of as a white hole we
we literally our entire universe is said
white hole
yeah that's a very profound thought
actually
uh there are fundamental ways
in which the mathematics of a finite
universe now by the way there might be
infinite universes but
the mathematics of a finite what we call
closed universe
like the 3d example of a balloon
is very similar to the mathematics of a
black hole
nothing can ever escape from this finite
volume this universe just like nothing
can ever escape
from a black hole okay it's just that
it's an expanding universe it was born
for reasons we don't yet understand
as an explosion but in a similar way you
can actually have a black hole within
our universe that initially is expanding
later on it'll go clunk and it'll
collapse but
you can create an initially expanding
black hole no problem
so in many ways the mathematics is
similar our universe can be thought of
as a black hole the fundamental
distinction
is that in our real universe a black
hole
is an object a structure where you've
compressed the matter
within this room for example and the
black hole
exists within the room that's
different from the whole universe being
the black hole
do you see the distinction there it's
kind of subtle a black hole
in our universe versus the whole
universe being
a black hole there is a difference but
mathematically there are a lot of
similarities
and there have been theoretical
physicists who have been exploring
that idea of our universe as being in a
sense
the ultimate black hole yeah oh man this
stuff is so
interesting and the i
i struggle with one idea which is
you can be anything you want to be but
not everything and
it really really bothers me that none of
us will live long enough to see
all of the answers um but
when i start thinking about the the
notion of
einstein sort of in the later years of
his life being trapped by his own
ideology
and really struggling with the
consequences of some of his own theories
um that gets really terrifying talk to
me about
how so even in this conversation
i form a notion and then you'll say
something and ah that notion
crumbles apart and now i have to form a
new notion
how do we stay open-minded enough so
that
as you get more advanced in your career
you have deeper wisdom you have more
sort of threads to pull on but you're
also more likely to have woven a false
tapestry that traps you
what do you do to be open to that new
information
yeah yeah it it's um
this is a this is a disease that
afflicts
quite a few scientists theoretical
physicists
like einstein who become very
set in their ways i mean einstein was a
real revolutionary when he was young he
was thinking of all these ideas
that other people thought were crazy
and his weakness later in life was that
he became so
wedded as you said to his
tapestry that he wasn't willing to
accept
new ideas and the fundamental idea that
he was not willing to accept
was quantum physics ironically because
of his many gigantic breakthroughs
that's the one
for which he actually won the nobel
prize for an explanation of something
called the photoelectric effect
that's a quantum effect he explained it
won the nobel prize for that
not for special relativity not for
general relativity
and yet an inability to come to grips
what
with what quantum mechanics was trying
to tell us about nature
was his fundamental problem while he was
trying to come up with a theory of
everything
it really didn't have quantum mechanics
so we have to
take those historical cases and keep
them
front and center in mind
work hard at maintaining an open mind so
you don't get fossilized
so you don't get set in your ways and i
would say that experimental physicists
and observational astronomers such as
myself i'm not a theorist
though i like theory we don't
fall victim to that as often as the
theorists because
we get better and better with time in
some ways an experimental physicist
learns more mistakes and how to avoid
them
so does an observational astronomer we
build upon our past
experiences and thus are able to do our
jobs in many ways
better with time
but the true blue sky thinking theorist
has to watch out
for this affliction and consciously
work at keeping an open mind yep
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all right let's talk about the thing
that trapped einstein so i know the
thing that he really pushed back on
is what he called spooky action at a
distance um can you describe that
for people absolutely yeah it's
it's the essence of quantum mechanics uh
and
very very spooky in
special relativity einstein showed quite
conclusively and this has now been uh
verified with
thousands if not millions of experiments
that
no material particle with non-zero mass
okay a photon a carrier of light has
zero mass by the way
it travels at the speed of light but no
particle with non-zero mass
can reach the speed of light let alone
exceed it
because it would take an infinite amount
of energy to do so
and as i said you know large hadron
collider
the stanford linear accelerator fermi
lab near chicago
all these accelerators have validated
that concept
over and over and over again takes a
huge amount of energy to get particles
going at close to the speed of light
we can't get them to reach the speed of
light
the problem in quantum physics is that
if you create
a part two two particles out of one
and let's say that that first particle
wasn't spinning at all there's uh you
know particles can spin
sort of like tops in quantum physics
it's a bit more complicated than that
but
think of it as spinning if the particle
originally isn't spinning
but then you create two particles one of
which is spinning
clockwise and the other one
counterclockwise
as seen from above let's say spin up and
spin down
quantum mechanics says that until a
measurement
is made you don't know which way the
particle
this one is spinning up or down
clockwise or counterclockwise
or this one and it's not just that
we don't know the particle doesn't know
and what that's really saying is that
the particle
is a quantum superposition of both
spin up and spin down it's both states
simultaneously until a measurement is
made
at which point it has to adopt one of
the two states by a process that in
quantum mechanics
is still not well described it's not
described for example by the schrodinger
equation it's a bit of a mystery
nevertheless once you make a measurement
spin up let's say the other particle
has to be spinned down instantaneously
in order for them