<p>Send two pulses of whatever (light, radio) you are using for communication, one a factor of <span class="math-container">$\alpha$</span> longer than the other.</p>

CC BY-SA 4.0
2020-12-16T00:57:55.367Z
That strikes me as really inefficient and unlikely to work.  Absorption and scattering in the interstellar medium varies with wavelength, and not all wavelengths are equally easy/hard to produce, which is a significant concern when you're already using massive amounts of power just to transmit a detectable signal at optimum wavelengths.  Plus how would the aliens know to look at either signal?  Even if one is on the objective optimal band, now you've gotta hope the aliens are thinking the same thing you are and monitor both the $\alpha$ and $1/\alpha$ wavelengths.
zibadawa timmy
CC BY-SA 4.0
2020-12-16T02:12:25.440Z
How about continuous transmission on two nearby frequencies with $\frac{\Delta f}{f} = \alpha$? or $\frac{\Delta \lambda}{\lambda} = \alpha$ or $f_+/f_- = 1+\alpha$ or...
uhoh
CC BY-SA 4.0
2020-12-16T14:21:40.137Z
I meant longer pulse, not longer wavelength. So an alternation of (say) 1 minute and 137+ minute pulses with a suitable gap in between.
Steve Linton
CC BY-SA 4.0
2020-12-15T23:47:44.973Z
2020-12-15T23:47:44.973Z
Steve Linton
<p>We've already attempted to communicate with aliens (and I don't mean teenagers), notably using <a href="https://en.wikipedia.org/wiki/Voyager_Golden_Record" rel="nofollow noreferrer">Voyager 1 and 2 and their &quot;gold records&quot;</a>.  Any intelligent technological civilization should easy decode it (although I'm not sure what they could usefully make of the audio).  Communicating a number is easy - finding aliens is the tricky part. :-)</p>
<blockquote>
<p>I have heard an argument that when we encounter intelligent aliens sending the α at them is the best way to let them know how much we know.</p>
</blockquote>
<p>This is entirely dependent on how far apart we are.  If we've sent a signal or message light years they already have a good idea of our technological level.  Working out the fine structure constant is not really difficult.  They'd be much more impressed by us sending a message over such a distance (or maybe not if they consider whatever method we use as primitive).</p>
<p>But if we're communicating over those distances then, courtesy of the limitation of the speed of light, we're not going to be telling them what we know, but one small part of what we <em>knew</em> when we sent the message.</p>

CC BY-SA 4.0
2020-12-16T08:08:18.857Z
2020-12-16T08:08:18.857Z
StephenG - Help Ukraine
<p>Sorry if this is not the right question for this channel, I just need to know and there is no good place to ask.</p>
<p>It is said the Fine Structure Constant α is one of the most fundamental constants in nature. Unlike the likes of the speed of light, α is dimensionless. I have heard an argument that when we encounter intelligent aliens sending the α at them is the best way to let them know how much we know. It was said that we should of course send the constant in the binary numeral system.</p>
<p>My question is: how do you communicate a fraction (α = roughly 1/137) in binary so that even aliens can decode it?</p>

CC BY-SA 4.0
2020-12-16T02:56:08.570Z
I’m voting to close this question because it is probably more suited to [worldbuilding.se] and is not really an astronomy question.
StephenG - Help Ukraine
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2020-12-16T06:13:44.080Z
@StephenG "more suited" is never a close reason. We only vote to close if we think it is *off topic* here. OP decides where to ask, moderators decide where to migrate. **voting to keep open!**
uhoh
CC BY-SA 4.0
2020-12-16T06:30:20.093Z
[Shall we continue to agree that good SETI and extraterrestrial questions are on-topic? What about METI?](https://astronomy.meta.stackexchange.com/q/644/7982)
uhoh
CC BY-SA 4.0
2020-12-16T08:40:28.643Z
As bits. In base-2. Or, sending 137 single thing.
peterh
CC BY-SA 4.0
2020-12-16T19:57:57.470Z
Much more complicated messages than a decimal point have already been sent.  I'm not sure precisely how a decimal point would be communicated via binary, but it shouldn't be hard to do.   Info on the Arecibo message here: 
  https://en.wikipedia.org/wiki/Arecibo_message
userLTK
<extra-terrestrial><seti><communication>
How to communicate Fine Structure Constant to aliens?
daniel.sedlacek
# How to communicate Fine Structure Constant to aliens?

(Asked by: username_0 on 2020-12-15)

Sorry if this is not the right question for this channel, I just need to know and there is no good place to ask.

It is said the Fine Structure Constant α is one of the most fundamental constants in nature. Unlike the likes of the speed of light, α is dimensionless. I have heard an argument that when we encounter intelligent aliens sending the α at them is the best way to let them know how much we know. It was said that we should of course send the constant in the binary numeral system.

My question is: how do you communicate a fraction (α = roughly 1/137) in binary so that even aliens can decode it?

**Tags:** extra-terrestrial, seti, communication

> **Comments:**
> **username_1**: I’m voting to close this question because it is probably more suited to [worldbuilding.se] and is not really an astronomy question.  
> **username_2**: @StephenG "more suited" is never a close reason. We only vote to close if we think it is *off topic* here. OP decides where to ask, moderators decide where to migrate. **voting to keep open!**  
> **username_2**: [Shall we continue to agree that good SETI and extraterrestrial questions are on-topic? What about METI?](https://astronomy.meta.stackexchange.com/q/644/7982)  
> **username_3**: As bits. In base-2. Or, sending 137 single thing.  
> **username_4**: Much more complicated messages than a decimal point have already been sent.  I'm not sure precisely how a decimal point would be communicated via binary, but it shouldn't be hard to do.   Info on the Arecibo message here:    https://en.wikipedia.org/wiki/Arecibo_message  

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## 2 answers

### Answer by username_5 on 2020-12-15. Score: 3

Send two pulses of whatever (light, radio) you are using for communication, one a factor of $\alpha$ longer than the other.

> **Comments:**
> **username_6**: That strikes me as really inefficient and unlikely to work.  Absorption and scattering in the interstellar medium varies with wavelength, and not all wavelengths are equally easy/hard to produce, which is a significant concern when you're already using massive amounts of power just to transmit a detectable signal at optimum wavelengths.  Plus how would the aliens know to look at either signal?  Even if one is on the objective optimal band, now you've gotta hope the aliens are thinking the same thing you are and monitor both the $\alpha$ and $1/\alpha$ wavelengths.  
> **username_2**: How about continuous transmission on two nearby frequencies with $\frac{\Delta f}{f} = \alpha$? or $\frac{\Delta \lambda}{\lambda} = \alpha$ or $f_+/f_- = 1+\alpha$ or...  
> **username_5**: I meant longer pulse, not longer wavelength. So an alternation of (say) 1 minute and 137+ minute pulses with a suitable gap in between.  

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### Answer by username_1 on 2020-12-16. Score: 2

We've already attempted to communicate with aliens (and I don't mean teenagers), notably using [Voyager 1 and 2 and their "gold records"](https://en.wikipedia.org/wiki/Voyager_Golden_Record). Any intelligent technological civilization should easy decode it (although I'm not sure what they could usefully make of the audio). Communicating a number is easy - finding aliens is the tricky part. :-)

> I have heard an argument that when we encounter intelligent aliens sending the α at them is the best way to let them know how much we know.

This is entirely dependent on how far apart we are. If we've sent a signal or message light years they already have a good idea of our technological level. Working out the fine structure constant is not really difficult. They'd be much more impressed by us sending a message over such a distance (or maybe not if they consider whatever method we use as primitive).

But if we're communicating over those distances then, courtesy of the limitation of the speed of light, we're not going to be telling them what we know, but one small part of what we *knew* when we sent the message.


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