Interesting interview with Freeman Dyson. He originally used the na...
This paper constitutes the first attempt to formalize the concept o...
Even if the civilization living in the Dyson sphere did its best to...
To determine the radiation emitted by the sphere we use Wien's Law ...
There's a problem in the argument of Cocconi and Morrison. They ass...
It's interesting because we can now test Freeman's assumption regar...
There are a few things extra things we can discuss about the Dyson ...
After Freeman Dyson published this paper [SETI](https://en.wikipedi...
Freeman Dyson is an English-born American theoretical physicist and...
Reports
Search
for
Artificial
Stellar
Sources
of
Infrared
Radiation
A
bstract. If
extraterrestrial
intelligent
beings
exist
and
have
reached
a
high
level
of
technical
development,
one
by-product
of
their
energy
metabolism
is
likely
to
be
the
large-scale
conversion
of
starlight
into
far-infrared
radiation.
It
is
proposed
that
a
search
for
sources
of
infrared
radiation
should
accompany
the
recently
initiated
search
for
interstellar
radio
communica-
tions.
Cocconi
and
Morrison
(1)
have
called
attention
to
the
importance
and
feasi-
bility
of
listening
for
radio
signals
trans-
mitted
by
extraterrestrial
intelligent
be-
ings.
They
propose
that
listening
aerials
be
directed
toward
nearby
stars
which
might
be
accompanied
by
planets
car-
rying
such
beings.
Their
proposal
is
now
being
implemented
(2).
The
purpose
of
this
report
is
to
point
out
other
possibilities
which
ought
to
be
considered
in
planning
any
serious
search
for
evidence
of
extraterrestrial
intelligent
beings.
We
start
from
the
notion
that
the
time
scale
for
industrial
and
technical
development
of
these
be-
ings
is
likely
to
be
very
short
in
com-
parison
with
the
time
scale
of
stellar
evolution.
It
is
therefore
overwhelming-
ly
probable
that
any
such
beings
ob-
served
by
us
will
have
been
in
existence
for
millions
of
years,
and
will
have
al-
ready
reached
a
technological
level
sur-
passing
ours
by
many
orders
of
mag-
nitude.
It
is
then
a
reasonable
working
hypothesis
that
their
habitat
will
have
been
expanded
to
the
limits
set
by
Mal-
thusian
principles.
We
have
no
direct
knowledge
of
the
material
conditions
which
these
beings
would
encounter
in
their
search
for
lebensraum.
We
therefore
consider
what
would
be
the
likely
course
of
Instructions
for
preparing
reports.
Begin
the
re-
port
with
an
abstract
of
from
45
to
55
words.
The
abstract
should
not
repeat
phrases
employed
in
the
title.
It
should
work
with
the
title
to
give
the
reader
a
summary
of
the
results
presented
in
the
report
proper.
Type
manuscripts
double-spaced
and
submit
one
ribbon
copy
and
one
carbon
copy.
Limit
the
report
proper
to
the
equivalent
of
1200
words.
This
space
includes
that
occupied
by
illustrative
material
as
well
as
by
the
references
and
notes.
Limit
illustrative
material
to
one
2-column
fig-
ure
(that
is,
a
figure
whose
width
equals
two
col-
umns
of
text)
or
to
one
2-column
table
or
to
two
I-column
illustrations,
which
may
consist
of
two
figures
or
two
tables
or
one
of
each.
For
further
details
see
"Suggestions
to
Contrib-
utors"
[Science
125,
16
(1957)].
3
JUNE
1960
events
if
these
beings
had
originated
in
a
solar
system
identical
with
ours.
Tak-
ing
our
own
solar
system
as
the
model,
we
shall
reach
at
least
a
possible
pic-
ture
of
what
may
be
expected
to
hap-
pen
elsewhere.
I
do
not
argue
that
this
is
what
will
happen
in
our
system;
I
only
say
that
this
is
what
may
have
happened
in
other
systems.
The
material
factors
which
ultimate-
ly
limit
the
expansion
of
a
technically
advanced
species
are
the
supply
of
mat-
ter
and
the
supply
of
energy.
At
present
the
material
resources
being
exploited
by
the
human
species
are
roughly
lim-
ited
to
the
biosphere
of
the
earth,
a
mass
of
the
order
of 5
X
10'
grams.
Our
present
energy
supply
may
be
gen-
erously
estimated
at
1
0'
ergs
per
sec-
ond.
The
quantities
of
matter
and
en-
ergy
which
might
conceivably
become
accessible
to
us
within
the
solar
system
are
2
x
1030
grams
(the
mass
of
Jupiter)
and
4
X
1033
ergs
per
second
(the
total
energy
output
of
the
sun).
The
reader
may
well
ask
in
what
sense
can
anyone
speak
of
the
mass
of
Jupiter
or
the
total
radiation
from
the
sun
as
being
accessible
to
exploitation.
The
following
argument
is
intended
to
show
that
an
exploitation
of
this
mag-
nitude
is
not
absurd.
First
of
all,
the
time
required
for
an
expansion
of
population
and
industry
by
a
factor
of
1012
is
quite
short,
say
3000
years
if
an
average
growth
rate
of
1
percent
per
year
is
maintained.
Second,
the
energy
required
to
disassemble
and
rearrange
a
planet
of
the
size
of
Jupiter
is
about
1044
ergs,
equal
to
the
energy
radiated
by
the
sun
in
800
years.
Third,
the
mass
of
Jupiter,
if
distributed
in
a
spherical
shell
revolving
around
the
sun
at
twice
the
Earth's
distance
from
it,
would
have
a
thickness
such
that
the
mass
is
200
grams
per
square
centimeter
of
surface
area
(2
to
3
meters,
depending
on
the
density).
A
shell
of
this
thickness
could
be
made
comfortably
habitable,
and
could
contain
all
the
machinery
re-
quired
for
exploiting
the
solar
radiation
falling
onto
it
from
the
inside.
It
is
remarkable
that
the
time
scale
of
industrial
expansion,
the
mass
of
Jupiter,
the
energy
output
of
the
sun,
and
the
thickness
of
a
habitable
bio-
sphere
all
have
consistent
orders
of
magnitude.
It
seems,
then,
a
reasonable
expectation
that,
barring
accidents,
Malthusian
pressures
will
ultimately
drive
an
intelligent
species
to
adopt
some
such
efficient
exploitation
of
its
available
resources.
One
should
expect
that,
within
a
few
thousand
years
of
its
entering
the
stage
of
industrial
develop-
ment,
any
intelligent
species
should
be
found
occupying
an
artificial
biosphere
which
completely
surrounds
its
parent
star.
If
the
foregoing
argument
is
ac-
cepted,
then
the
search
for
extraterres-
trial
intelligent
beings
should
not
be
confined
to
the
neighborhood
of
visible
stars.
The
most
likely
habitat
for
such
beings
would
be
a
dark
object,
having
a
size
comparable
with
the
Earth's
or-
bit,
and
a
surface
temperature
of
2000
to
3000K.
Such
a
dark
object
would
be
radiating
as
copiously
as
the
star
which
is
hidden
inside
it,
but
the
radiation
would
be
in
the
far
infrared,
around
10
microns
wavelength.
It
happens
that
the
earth's
atmos-
phere
is
transparent
to
radiation
with
wavelength
in
the
range
from
8
to
12
microns.
It
is
therefore
feasible
to
search
for
"infrared
stars"
in
this
range
of
wavelengths,
using
existing
tele-
scopes
on
the
earth's
surface.
Radiation
in
this
range
from
Mars
and
Venus
has
not
only
been
detected
but has
been
spectroscopically
analyzed
in
some
de-
tail
(3).
I
propose,
then,
that
a
search
for
point
sources
of
infrared
radiation
be
attempted,
either
independently
or
in
conjunction
with
the
search
for
artificial
radio
emissions.
A
scan
of
the
entire
sky
for
objects
down
to
the
5th
or
6th
magnitude
would
be
desirable,
but
is
probably
beyond
the
capability
of
ex-
isting
techniques
of
detection.
If
an
un-
directed
scan
is
impossible,
it
would
be
worthwhile
as
a
preliminary
measure
to
look
for
anomalously
intense
radiation
in
the
10-micron
range
associated
with
visible
stars.
Such
radiation
might
be
seen
in
the
neighborhood
of
a
visible
star
under
either
of
two
conditions.
A
race
of
intelligent
beings
might
be
un-
able
to
exploit
fully
the
energy
radiated
by
their
star
because
of
an
insufficiency
of
accessible
matter,
or
they
might
live
in
an
artificial
biosphere
surrounding
one
star
of
a
multiple
system,
in
which
one
or
more
component
stars
are
un-
suitable
for
exploitation
and
would
still
be
visible
to
us.
It
is
impossible
to
guess
the
probability
that
either
of
these
cir-
cumstances
would
arise
for
a
particular
race
of
extraterrestrial
intelligent
be-
ings.
But
it
is
reasonable
to
begin
the
search
for
infrared
radiation
of
artifi-
cial
origin
by
looking
in
the
direction
of
nearby
visible
stars,
and
especially
in
the
direction
of
stars
which
are
known
to
be
binaries
with
invisible
com-
panions.
FREEMAN
J.
DYSON
Institute
for
Advanced
Study,
Princeton,
New
Jersey
1667
on September 19, 2012www.sciencemag.orgDownloaded from
... but Dyson is not speaking of a sphere in a geometrical sense, he is speaking of a biosphere. He is asking us to look for Dyson artificial biospheres in the form of a ring, actually.
True, but Dyson in the paper suggests a radius of 2 AU ("...revolving around the sun at twice the Earth's distance..."), which would give about 277 K.
Cool to think about the sphere size for only radiation at the CMB, though - thanks for that!
There's a problem in the argument of Cocconi and Morrison. They assume the extraterrestrial beings would be to some extent cooperative in the sense that they would use radio signals to communicate between them and possibly with us. Freeman's idea allows us to search for extraterrestrial life even if they are not cooperative.
Hi, I may be misinterpreting here but what is the solid angle/volume element you're considering when you talk about the section of mass?
\begin{equation}
dm = \rho *dV
\end{equation}
\begin{equation}
dV = \pi (r \theta)^2d
\end{equation}
In other words, where is your $dV$ coming from?
It's interesting because we can now test Freeman's assumption regarding the world's energy consumption.
In 2013 the estimated world energy consumption was $1.8 \times 10^{20}$ erg per second. This means the average growth since 1960 was 1.1%! Freeman's prediction has been right for the past 57 years.
To determine the radiation emitted by the sphere we use Wien's Law - the black body radiation curve peaks at a wavelength inversely proportional to the temperature.
$$
\lambda_{max} = \frac{b}{T}
$$
where b is the Wien's displacement constant: $2.898×10^{−3}mK$.
For this Dyson Sphere, if we replace T with 300 K we get$\lambda_{max} \approx 10 $ microns.
After Freeman Dyson published this paper [SETI](https://en.wikipedia.org/wiki/Search_for_extraterrestrial_intelligence) started searching for "infrared heavy" spectra from solar analogs. As of 2005 Fermilab has an ongoing survey for such spectra by analyzing data from the Infrared Astronomical Satellite (IRAS). So far Fermilab discovered 17 potential "ambiguous" candidates, of which four have been named "amusing but still questionable".
The last event was on August 25th 2016, when scientists observed dimmings of up to 65% in a young M-type pre-main-sequence star with a resolved disk. The researchers hypothesize that the irregular dimmings are caused by either a warped inner-disk edge or transiting cometary-like objects in either circular or eccentric orbits.
Freeman Dyson is an English-born American theoretical physicist and mathematician. He is professor emeritus at the Institute for Advanced Study and worked on several areas including quantum electrodynamics, solid-state physics, astronomy and nuclear engineering. 
Interesting interview with Freeman Dyson. He originally used the name **"Artificial Biosphere"** to describe an inhabited alien region that would radiate in the infrared band but **science fiction writers started using the term "Dyson Sphere"** to describe this concept.
[](https://www.youtube.com/watch?v=GPB775_BZlw)
This paper constitutes the first attempt to formalize the concept of a Dyson Sphere. A Dyson Sphere is a hypothetical structure that an advanced civilization
might build around a star to intercept all of the star’s light
for its energy needs.
Freeman Dyson argues that a way to look for extraterrestrial life is to search for the presence of Dyson Spheres.
The basic idea is that as a civilization evolves it will have increasingly energy requirements. Once all the resources of the home planet have been explored the next obvious step is to get energy from the closest star.
According to the Kardashev scale there are 3 types of civilizations based on the amount of energy a civilization is able to use:
- **Type I** - can use and store all of the energy which reaches its planet from its parent star.
- **Type II** - can harness the total energy of its planet's parent star.
- **Type III** - can control energy on the scale of its entire host galaxy.
Humans are currently a Type 0 civilization and Michio Kaku predicts that we attain Type I status in 100–200 years, Type II status in a few thousand years, and Type III status in 100,000 to a million years.
From 1960 to 2021 I got an annual compounded growth rate of around 2.4%, which, I believe is what Dyson meant with his "average growth rate of 1 percent" as compounded over 3000 iterations it arrives at a factor of 10^12. So we've actually been surpassing his prediction and should disassemble Jupiter within 1300 to 1500 years from now?
@Gregor Gross: Dyson specifically mentions on this paper a "spherical shell revolving around the sun". I believe the ring designs (and all others) came after this paper was published. As Dyson himself said on the video above: thinking big!
I have to admit I was surprised when I heard of this different ways of understand a sphere as well. And I can't find the reference anymore, even as I collect these references quite strictly usually. If I remember correctly, it was mentioned in this regard that it's not so easy to build an entire sphere around a sun because of material stress by weight and heat radiation. Also, the material itself is really alot when it's a full sphere around a sun, whereas a ring around it is still colossal, but within realistic reach. And a ring around the sun already offers the space of 10,000 Earth or so?
There are a few things extra things we can discuss about the Dyson Sphere:
### Can the Dyson Sphere break due to gravity?
To calculate the stress on the sphere let's first consider a small section with angular radius $\theta << 1$.
The mass of the section is just $m=\pi (r\theta)^2d\rho$, where $\rho$ is the density of the material and d is its thickness. The stress will generate a force pointing outwards with magnitude $2\pi(r\theta)T\sin \theta$ (where T is the force per unit length) that will oppose the gravitational force of the star.
$$
2\pi(r\theta)T\sin \theta = \frac{GM\pi r^2 \theta^2 d \rho}{r^2}
$$
Since $\theta << 1$, $\sin \theta \approx \theta$ and
$$
T = \frac{GM \rho}{2rd}
$$
The Pressure is just $P=Td=\frac{GM \rho}{2r}$, which for a our Dyson Sphere is around $2.4\times10^{12}$ N/m$^2$. Such material strength is very difficult to attain since a typical chemical bond can resist a force of the order of 1 eV/Å ≈ 10$^{−9}$ N. The unit area will have of the order of $10^{20}$ chemical bonds in the perpendicular direction, hence can support at most ∼ $10^{11}$ N, even if all the bonds are perfectly aligned without any imperfections in the molecular structure, and are able to share the load equally.
### Stability
The way to look at the stability question is to analyze the force applied inside the sphere using Gauss's Law: the flux of the force field across an arbitrary closed surface is proportional to the amount of mass inside it.
$$
\int F dA \propto \rho
$$
Since there's no mass inside the closed surface the integral is zero, which means the force inside the Dyson Sphere is also zero.
This might be dangerous because any force applied on the sphere (e.g meteor collision) will cause it to drift and eventually hit the star.
### It can convert energy from trash
Any trash released from the sphere would immediately fall into the star turning into energy. There's a potential danger in dumping too much waste into the star as it might push it over the mass limit of instability setting off a Supernova.
### Other types of structures
After this paper was published people came up with other hypothetical structures such as:
- **RingWorlds** - Introduced by Larry Niven, a ringworld is band encircling a band encircling a star, rotating to create gravity and covered with an ecosphere.
- **Submerged Dyson Spheres** - these structures were proposed by Nick Szabo and are spheres built considerably closer to the star. These spheres would solve the communication delay problem that occurs in a "normal" Dyson Sphere due to its size and would also be more suitable for advanced "solid state civilizations".
Even if the civilization living in the Dyson sphere did its best to store available energy, the sphere would eventually start increasing its temperature and radiating energy away until thermal equilibrium is reached.
We can assume that the sphere is a black body (it absorbs all incident electromagnetic radiation from the star) and in thermal equilibrium it behaves according to the [Stefan–Boltzmann law](https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law):
$$
P=\sigma A T^4
$$
where $\sigma = 5.67 \times 10^{-8}\text{Wm$^{-2}$K$^{-4}$}$ is the Stefan-Boltzmann constant, A is the area of the body, P is the total power emitted by the body and T is the temperature of the body.
For a Dyson sphere with the size of Earth's orbit (1AU = $1.5\times 10^{11}$m) the temperature of the sphere is just
$$
T = \sqrt[4]{\frac{3.8\times 10^{26}}{5.67 \times 10^{-8}4 \pi (1.5\times 10^{11})^2}} \approx 393 K (120^{\circ}C)
$$
Note that P is just the power output of the Sun: $3.8\times 10^{26} W$.
Although 393 K is still very hot for a Earthlike environment, there are still a few factors that we haven't considered and that might decrease the temperature such as rotation of the Dyson Sphere (Earth's rotation contributes to decrease the temperature at the surface of the planet, halving its energy flux).
That's why Freeman Dyson concludes the temperature of the sphere falls in the interval 200 K - 300 K.
Note that if someone wanted to design an invisible sphere - something that would radiate at the same temperature as the Cosmic Microwave Background Radiation (2.73 K) - it would have a radius of 328 light years!