00:00:00
for quite a long time the sort of
00:00:02
adopted agreed definition for the edge
00:00:04
of space has been something called the
00:00:06
carmen line
00:00:07
which is located at 100 kilometers above
00:00:10
the earth's surface it is not a legal
00:00:12
definition but it's a definition that's
00:00:14
been adopted by the federation
00:00:16
international aeronautic which is the
00:00:19
world air sports federation but it's
00:00:21
it's a largely unsatisfying definition
00:00:24
because of course the atmosphere doesn't
00:00:27
have an edge it's a continuous
00:00:30
fluid body it has lots of different
00:00:33
properties in lots of different regions
00:00:34
but none of them have rigidly defined
00:00:37
edges and in fact the properties change
00:00:39
as a function of time and solar activity
00:00:42
and lots of other things 100 seems
00:00:44
almost too perfect doesn't it it does so
00:00:46
recently a paper's been published called
00:00:49
the edge of space revisiting the carmen
00:00:51
line and this was work done by an
00:00:53
astrophysicist named jonathan mcdowell
00:00:56
at the harvard smithsonian center for
00:00:57
astrophysics and he takes a closer look
00:01:00
into whether there is a real scientific
00:01:03
definition for the karman line the
00:01:05
original carmen line definition was
00:01:08
roughly associated with the idea that
00:01:10
there's a boundary between
00:01:12
where aeronautical forces stop and you
00:01:15
no longer get lift in the atmosphere
00:01:18
aeronautical lift is a mechanical force
00:01:20
it's generated by contact with the fluid
00:01:23
the fluid obviously being the atmosphere
00:01:25
and if you run out of fluid you run out
00:01:27
of force and so at the carbon line it
00:01:31
you're you're sort of where an aircraft
00:01:32
would have to travel at a speed that's
00:01:35
greater than the orbital velocity
00:01:37
in order to get enough lift from its
00:01:39
wings to stay in the air so in this
00:01:41
paper we looked at the orbits of 43 000
00:01:44
satellites have been tracked over the
00:01:46
years and of course most of them are way
00:01:48
above the karman line but there were
00:01:50
substantial numbers that throughout
00:01:52
their orbit would pass below the 100
00:01:55
kilometer line getting even closer to 80
00:01:57
kilometers and not just on their last
00:01:59
orbit before they disintegrated but they
00:02:01
had multiple passages this low and so
00:02:03
right away you can say okay well the 100
00:02:06
kilometer line doesn't make a lot of
00:02:07
sense you can't have a satellite in
00:02:09
orbit and then it comes in and oh for a
00:02:10
little bit it's not in space and then it
00:02:12
goes back into space and and on and on
00:02:14
and on and so right there is some
00:02:16
evidence to at least support the idea of
00:02:18
revisiting this definition so the second
00:02:20
thing he did was actually use an
00:02:22
atmospheric model and actually make the
00:02:25
calculations of for a typical satellite
00:02:29
where would the drag forces
00:02:31
um be enough to sort of cause it to fall
00:02:34
back to earth so like the death zone
00:02:37
the death stone for satellites that's
00:02:38
exactly it so the conclusion he makes is
00:02:40
that for a typical kind of space vehicle
00:02:44
the gravity will exceed the aerodynamic
00:02:46
forces for any object in steady flight
00:02:49
at that altitude that altitude lies in
00:02:52
about the 70 to 90 kilometer range so he
00:02:55
factors in the time variation and all of
00:02:57
this stuff and and finds a range for
00:03:00
this limit but notes that it's always
00:03:03
well below that 100 kilometer line this
00:03:06
is just one argument other arguments
00:03:08
would look at the structure of the
00:03:10
atmosphere which is quite complicated
00:03:12
but again it's divided into specific
00:03:15
layers
00:03:16
mostly
00:03:17
based on where the gradient in
00:03:20
temperature changes these are called
00:03:22
pauses and so at about 85 kilometers
00:03:25
we've got the mesopause which is the
00:03:27
boundary between the mesosphere and the
00:03:30
thermosphere and that marks the point
00:03:32
which is the coldest point in the
00:03:34
atmosphere below that point
00:03:37
the chemical pump position of the
00:03:38
atmosphere is mostly steady and above
00:03:42
that you've got different molecules
00:03:43
moving in different ways and so from
00:03:46
atmospheric physics there's also a
00:03:48
boundary more towards the 80 kilometer
00:03:50
line so what's really interesting about
00:03:52
this argument is to actually appreciate
00:03:55
how close space is because 80 kilometers
00:03:59
100 kilometers that's not that far away
00:04:01
you can easily drive that in an hour
00:04:04
so i thought it might be fun to look on
00:04:05
a map and actually appreciate um to
00:04:09
scale how how how far away space is of
00:04:12
course our map is centered on the center
00:04:14
of the universe which is here in
00:04:15
nottingham and the unit that we're going
00:04:18
to use to mark scale on this map
00:04:21
is the humble lego block the height of
00:04:23
this brick is 3.2 millimeters and so
00:04:27
i've printed this map so that five of
00:04:29
these lego bricks
00:04:31
represent 100 kilometers on this map to
00:04:33
put some things into scale first let's
00:04:35
talk about airliners so when we're on a
00:04:37
commercial airliner we're traveling at
00:04:40
about an altitude of 10 to 12 kilometers
00:04:43
so when we're traveling on a commercial
00:04:44
airline we're not even traveling at the
00:04:47
height of this brick above this map so
00:04:49
the next scale i'm going to show you is
00:04:51
the world record for how high a human
00:04:54
being has jumped out of a balloon to
00:04:56
skydive down to earth so this record was
00:04:59
broken recently by alan eustis
00:05:02
and he jumped from a height of 41
00:05:04
kilometers so that would represent two
00:05:06
bricks on this map and so now we want to
00:05:09
go up to the karman line and so the
00:05:11
debate we're discussing today is whether
00:05:14
we define the edge of space at 80
00:05:17
kilometers which is here
00:05:20
or 100 kilometers which is
00:05:22
here doesn't seem that hard anyway does
00:05:25
it so i think that's the amazing thing
00:05:27
uh to appreciate so if this height is a
00:05:29
hundred kilometers what's really amazing
00:05:32
is how small this number actually is how
00:05:34
close we are to space so if i tip this
00:05:37
on this the edge and i've got 100
00:05:38
kilometer marker here you can see that
00:05:41
nottingham is closer to space than it is
00:05:43
to london and i can get that london in
00:05:45
an hour and a half on the train all
00:05:46
right so maybe nottingham to london
00:05:48
doesn't mean very much to you but if you
00:05:50
you're in new york you're closer to
00:05:52
space than you are to philadelphia
00:05:54
if you're in los angeles you're closer
00:05:56
to space than you are to san diego oh
00:05:59
let me do a canadian one okay
00:06:01
if you're in montreal you're closer to
00:06:03
space than you are to ottawa
00:06:05
i've got no idea where those places are
00:06:09
all right cool i looked up adelaide for
00:06:11
you but nothing's near adelaide so it
00:06:13
didn't work when do you become an
00:06:15
astronaut so
00:06:16
nasa gives its astronaut wings to anyone
00:06:21
who's trained and flown a successful
00:06:23
mission that reaches above 50 miles
00:06:26
which is 80 kilometers so that's
00:06:28
actually the lower limit and there's a
00:06:30
similar acknowledgement from the us
00:06:33
for civilians who have piloted a
00:06:36
successful flight above that line is
00:06:38
this important like is this just a bunch
00:06:40
of people writing papers or does it
00:06:42
matter where space starts and finishes
00:06:44
so
00:06:45
it it matters from a scientific
00:06:46
perspective because scientists like to
00:06:48
study these sorts of things so it's
00:06:50
perfectly understandable that people who
00:06:51
are interested in
00:06:53
atmospheric physics and the orbits of
00:06:56
satellites would care but it it actually
00:06:58
does have some wider issues that now
00:07:01
touch on issues of economics and
00:07:04
politics and defense and things like
00:07:06
that
00:07:07
so i mentioned there is no international
00:07:10
agreed legal definition of space there
00:07:13
have been for some time moves to make a
00:07:15
legal definition
00:07:16
but that's always been opposed by the
00:07:18
u.s
00:07:19
and you can understand why because from
00:07:22
a military point of view a government
00:07:24
wouldn't want to be restricted by
00:07:26
international space treaties
00:07:28
when it's trying to launch high altitude
00:07:31
ballistic missiles something like that
00:07:34
and what about space tourism i guess
00:07:35
they want it to be as low as possible so
00:07:36
they can sell their space flights well
00:07:38
that's the other issue so commercial
00:07:41
space tourism is becoming a thing now as
00:07:43
we film this virgin galactic has just
00:07:45
managed to pilot a vehicle to 82
00:07:48
kilometers by the nasa definition that
00:07:50
counts as entering space by the fai
00:07:53
definition it doesn't because they
00:07:54
haven't reached the karman line but it
00:07:56
would matter very very much to a
00:07:58
commercial enterprise to be able to
00:08:01
say that they can take people into space
00:08:03
now practically speaking
00:08:05
you know i think what you would want
00:08:07
from a space mission is the experience
00:08:09
of weightlessness and the experience of
00:08:11
looking out the window and seeing the
00:08:13
earth as a as a ball you would get that
00:08:15
from 80 kilometers as well as you would
00:08:17
from 100 kilometers but like i look at
00:08:19
that and i look at how low that is and i
00:08:21
imagine how come you can see the
00:08:23
curvature of the earth from such a that
00:08:25
doesn't seem that high i think partly
00:08:27
that's because i've printed a map out on
00:08:29
a flat piece of paper so in reality this
00:08:32
is a curved surface that i'm showing you
00:08:35
here you might not see it as a complete
00:08:37
ball but you would definitely see the
00:08:39
curvature of the earth you would
00:08:40
experience the earth as a sphere it
00:08:42
becomes
00:08:43
quite clear that for commercial
00:08:46
enterprise you're not going to want to
00:08:48
waste money and fuel and
00:08:50
increase risk by taking people up to 100
00:08:52
kilometers if they can get the same
00:08:54
experience going to 80 kilometers
00:08:56
but part of that experience for people
00:08:58
will be able will be being able to say i
00:09:01
have officially been to space where
00:09:04
would you be drawing the line well i'm
00:09:05
pretty convinced by this paper i mean it
00:09:07
has some pretty sound arguments from a
00:09:09
number of different directions so i
00:09:11
think if there was a move to redefine
00:09:13
the 80 kilometer line as the mcdowell
00:09:16
line i think that should go down very
00:09:18
well but but mcdowell says 70 to 90.
00:09:20
that's like super vague
00:09:22
well that's just because scientists you
00:09:24
you know scientists you've talked to
00:09:26
enough of us over the years and we like
00:09:28
our arab bars and we like our confidence
00:09:30
intervals but if you want to define a
00:09:33
line you might as well put it in the
00:09:35
middle of a region that is well-bounded
00:09:37
this paper has revisited the numbers and
00:09:40
the back of the envelope calculations
00:09:41
that gave 100
00:09:43
are now refined and they might not give
00:09:46
a more precise number but they at least
00:09:48
show us that it's not a hundred and so
00:09:51
it's
00:09:52
very unsatisfying to keep it at that
00:09:54
level i thought it would be fun to
00:09:55
actually build up a perspective on the
00:09:58
altitude that other objects in space get
00:10:01
part of this was motivated by the fact
00:10:03
that just last week i went outside as i
00:10:05
was coming home from work and happened
00:10:07
to see the international space station
00:10:08
go overhead it was really bright it was
00:10:10
a beautiful passage and as always i was
00:10:12
struck by looking up and thinking
00:10:14
oh my god there's human beings flying
00:10:16
above my head in orbit around the earth
00:10:18
that's pretty amazing how far away are
00:10:21
they actually up there the space shuttle
00:10:23
now no longer in existence but i
00:10:25
couldn't resist getting my lego out i
00:10:27
used to take astronauts up to the
00:10:29
international space station like may
00:10:31
jameson and that's at 400 kilometers
00:10:34
above the surface of the earth
00:10:36
so in
00:10:37
our lego bricks if this is a hundred we
00:10:39
need four times that amount
00:10:42
so
00:10:43
let's
00:10:44
do this 13
00:10:46
14
00:10:48
16 i feel like i'm on lego masters
00:10:52
20. excellent right so this is the orbit
00:10:56
at which human beings continuously
00:10:58
inhabit a space station orbiting the
00:11:02
earth
00:11:03
and even that is not that high i'm
00:11:05
slightly less impressed
00:11:08
that wasn't your goal was it
00:11:10
i think one of the values of human space
00:11:12
flight one of the real values is
00:11:14
cultural not scientific
00:11:16
and it's putting human beings high
00:11:18
enough to give them that perspective on
00:11:21
space
00:11:22
and if they only have to go that high
00:11:25
to be able to look out in one direction
00:11:28
and see nothing but the infinity of
00:11:30
space and then turn around and look down
00:11:33
and see the earth
00:11:35
in
00:11:36
enough scope
00:11:37
to see
00:11:38
not borders and not resources to be
00:11:40
exploited but to appreciate that this is
00:11:43
the one and only place where life in the
00:11:46
universe exists and to look out to the
00:11:48
horizon and appreciate
00:11:50
how razor thin that precious atmosphere
00:11:53
that keeps us safe is
00:11:55
then i think i think it's quite amazing
00:11:57
that you don't have to get that high up
00:11:59
to find a perspective where you realize
00:12:02
just how precarious and how delicate the
00:12:05
ecosystem and the geosystem on earth is
00:12:10
what else you want to show me you got
00:12:11
hubble there or okay so i've got uh
00:12:14
nancy roman and the hubble space
00:12:15
telescope one of my favorites
00:12:17
and this orbits at an altitude of 540
00:12:22
kilometers it used to be higher but it's
00:12:24
slowly even at that altitude it suffers
00:12:26
from accumulative
00:12:28
atmospheric drag over time so it's going
00:12:29
lower and lower and that represents
00:12:32
pretty much the highest altitude that
00:12:34
the space shuttle could reach because it
00:12:36
was hubble was designed to be put into
00:12:39
earth orbit at an altitude where the
00:12:41
space shuttle could repeatedly go and
00:12:43
service it and it's a good thing it did
00:12:45
because we benefited from those
00:12:47
servicing missions quite a lot and so
00:12:49
i've got 20 bricks now and i need to put
00:12:52
eight more to get up to the height of
00:12:55
the hubble space telescope so
00:12:56
one
00:12:59
two
00:13:02
three
00:13:03
five
00:13:06
now we've run out of thin bricks so
00:13:08
we're gonna put
00:13:10
three more on top and so that's how high
00:13:13
the hubble space telescope is
00:13:15
all right so there's the hubble space
00:13:17
telescope yeah there you go success not
00:13:20
to scale of course the whole space
00:13:21
telescope is about the size of the bus
00:13:23
not about the width of the united
00:13:24
kingdom what's higher than that well
00:13:26
there's lots of satellites up there in
00:13:27
orbit gps global positioning satellites
00:13:30
orbit at an altitude of 20 000
00:13:33
kilometers above the surface of the
00:13:35
earth that would require a thousand lego
00:13:37
bricks and i'm not going to build that
00:13:39
today
00:13:40
but i would just note that that would
00:13:42
take us 3.2 meters
00:13:44
above this map
00:13:46
okay so right through the ceiling up
00:13:48
there somewhere okay and these are
00:13:49
satellites they're in geosynchronous
00:13:51
orbits so they orbit the earth twice a
00:13:53
day but there are satellites that are
00:13:55
even further up they're called
00:13:56
geostationary orbits their orbital
00:13:58
period is matched with the rotation of
00:14:00
the earth so they orbit once a day which
00:14:02
means that they are effectively always
00:14:05
above the same location
00:14:07
above the equator and these are the
00:14:09
satellites that give us our weather meet
00:14:11
readings and our active our
00:14:14
communications relays on this scale
00:14:16
you'd need
00:14:17
1789 bricks which would take you 5.7
00:14:20
meters above
00:14:21
the table
00:14:22
all right well that's way up way up
00:14:24
we're looking here down at the uk and
00:14:26
europe how many bricks down is the other
00:14:29
side of the earth so i said that the gps
00:14:32
satellites are at a thousand bricks
00:14:34
above the earth um but the other side of
00:14:36
the earth would only be 640 bricks so
00:14:39
that's less than the height of the gps
00:14:41
satellites what about what if i wanted
00:14:42
to go to the moon of course you want to
00:14:44
go to the moon well you would need to
00:14:45
travel 19
00:14:47
220
00:14:48
lego bricks away which on this scale
00:14:51
would be 60 meters there's been enough
00:14:53
recent attention to this idea that the
00:14:56
karmann line needs to be redefined that
00:14:58
the organizations that deal with
00:15:00
aeronautical things and the organization
00:15:02
that deals with astronautical things are
00:15:05
proposing to get together in the coming
00:15:07
year to have a symposium to look at the
00:15:09
scientific and the political and
00:15:12
whatever other arguments go into this to
00:15:14
see if we need to actually have a
00:15:16
definition of where is space and what
00:15:18
that might be we made a video a couple
00:15:20
years ago saying voyagers left the solar
00:15:22
system and just left the solar system
00:15:23
again so most things in space don't have
00:15:26
a hard edge and that means that
00:15:28
different definitions can apply
00:15:31
and you can argue to until the cows come
00:15:33
home about whether pluto's a planet or
00:15:35
where the solar system ends or how big
00:15:38
is the milky way and to some extent you
00:15:40
will never get a satisfying answer
00:15:42
because
00:15:43
science often comes with caveats that
00:15:45
say it depends what you mean
00:15:50
i can tilt it but you'll notice that the
00:15:52
axis of the spin keeps pointing the same
00:15:56
direction it explains things but the
00:15:57
main thing it does is creates a huge
00:15:59
problem
00:16:00
because if you're a theoretical
00:16:01
physicist you can do a calculation that
00:16:02
says okay so i'm creating all these
00:16:04
virtual particles
