Transcript Reaching Out to ET

Theme 12 – SETI:
Reaching Out to ET
ASTR 101
Prof. Dave Hanes
Four Strategies for Contacting ET
- all four have been attempted!
Physical
Contact
Communication
Active
We travel or send
probes to the stars
We send signals to
the stars
Passive
We sit and await
visitors
We hunt for signals
from the stars
One Fundamental Problem
with Active Approaches
They take time, and may not yield a result for many centuries at
least. Who is willing to support this endeavour?
I. Active Communication
Light leakage (inadvertent):
The Problem
Our visible ‘glow’ is
feeble next to the Sun:
we won’t be seen
But at Other
Wavelengths!
Our radio broadcasts
‘leak’ out into space,
at wavelengths where
the Sun is ‘quiet.’ So
we show up!
to
Here, the Earth as it would be seen
from a nearby star. It varies because
different stations ‘rise and set’ thanks
the Earth’s rotation.
The Importance of Variability
A continuous ‘glow’ at any wavelength is
undistinguished, and could be from a
natural source (a star, a cloud of gas, …)
Radiation that is highly modulated (that is,
changing rapidly and in complex ways)
draws attention to itself and probably has a
non-natural origin.
In Short: To Be Noticed, Wave!
Strongly Modulated Signals
Include TV Broadcasts
…Some of Very High Quality
Things Are Changing
Television signals are now routinely distributed over fibre
networks, not broadcast from antennas. Less and less of
our broadcast energy flows out into space
But the first “I Love Lucy” broadcasts are already more
than 60 light years out in space, and early radio broadcasts
considerably farther.
(See the movie “Contact,” wherein early television
broadcasts from Nazi Germany first alert ET’s to our
presence here on Earth.)
How About Intentional Signals?
It is cheap and easy to send out a series of radio
‘blips’ in the form of dots-and-dashes to encode
some simple message.
This would not, of course, be anything like Morse
code, which represents the letters of a complex
alphabet, but rather as a set of 1’s and 0’s (just as
information in a computer is structured as ‘bits’).
Breaking the Code
Frank Drake once sent a card to his friends, with a string of 551
characters – just 1’s and 0’s, looking like so:
11111000010100100011001… etc
But why 551? It is a special kind of number: it is the product of
two prime numbers, 19 and 29. (Compare this number to, say,
640 = 320 x 2 = 160 x 4 = 80 x 8 = 40 x 16 = 20 x 32…).
So Frank’s message can be broken down into 19 rows of 29
characters, or 29 rows of 19 characters, but in no other way.
29 Rows of 19 Characters
Represent each “1” as a dark spot,
and each “0” as a light spot, and you
get a picture – greetings from Frank!
The picture has other information,
too: the sun at top left, nine planets
down the side (some of them big);
Carbon and Oxygen atoms at the top
right; a vertical measure (Frank’s
height!) at the lower right, most
logically interpreted in terms of the
wavelength of the radio signal; etc.
[By the way, this is essentially how TV
pictures are formed: encoded information
about different spots of brightness.]
A Real Message,
Sent to the Stars
[in 1974]
It is not expected that this
will
ever be received: it’s a purely
symbolic exercise, but it
reminds us how easily a
picture can incorporate a lot
of information.
Huge Advantages
This is the fastest communication possible! (it
travels at c, the speed of light)
It is cheap! (it takes literally only a few cents
worth of energy)
It has the potential for fantastic information
content! (Consider the information zooming
around wirelessly on the internet)
‘Interrupted’ Conversations
What Would We Tell Them?
“I would vote for Bach, all of Bach streamed
out into space, over and over again. We
would be bragging, of course… but we
could tell the harder truths later.”
...Lewis Thomas (a biologist, in 1977)
What Would We Like
to Learn About ET?
[a very incomplete list!]
Would they have :
-
a morality comparable to ours?
respect for individual freedoms?
similar understandings in maths and science?
similar‘world views’ in creative arts and philosophy?
a love (or even an understanding) of music?
religious beliefs? (many religions?)
a sense of humour?
a biology comparable to our own?
sexes?
unlimited lifespans?
So many questions!
But Remember Clarke’s Law
“Any sufficiently advanced technology will be indistinguishable
from magic.” (What would Neanderthal man make of a cell
phone?)
We have only just developed the technology that allows
interstellar communication; other ET civilizations are likely to be
more advanced than us. Suppose they have been there for
(say) ten thousand years – an astronomical blink of the eye.
They may have unimaginable abilities!
We may have little to offer them in the way of insights or to
capture their interest.
II. Active Physical Contact
We go to the stars (in manned or unmanned
spacecraft)
There are three almost insurmountable
problems:



the distances and energetics
getting through the interstellar medium
the human cost
Travel in the Solar System
Distance to moon = 1 light-second.
Travel time (Apollo 11 crew) ~ three days
Nearest star = 4 light years
- about 100 million times as far as the moon!
Nearest ET? Perhaps hundreds or thousands of
light years away. (But in what direction?)
Problem 1:
Distances and Energetics
The Fundamental Problem
Rockets need to carry with them the fuel that they
will need for later manoeuvres, consumables for
any astronauts on board, instrumentation and
guidance sytems, shielding, and so on.
Getting all that mass moving in the first place
takes fantastic energy, which is why we shed
unnecessary mass [= stages] as quickly as
possible.
Newton Can Help!
- but only to a limited extent
How About New Technologies?
The Most Efficient Fuel!
A Hypothetical Trip
We need 100,000 tons of matter and 100,000 tons of antimatter to deliver and return a 10-ton [!!] payload.
The exhaust is gamma rays!
Costly, Difficult and
Dangerous
How About
‘New Physics’?
- wormholes,
warp drives, etc…
Problem 2:
Moving Through the Interstellar Medium
Some Probes Are On Their Way!
[very slowly]
http://www.astro.queensu.ca/~hanes/ASTR101-Fall2015/ANIMS/Bach2.mp4
Greetings to the Universe
http://very.re-lab.net/voyagers.html
Problem 3:
The Human Cost
Will we never go to the stars?