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andrel wrote:
> No, differential time- and lightspeeds are incompatible with lorentz
> invariance of physical laws, because they should be invariant under
> translation and uniform velocity changes.
I see what you mean. Yes, I agree. My bad.
--
Darren New, San Diego CA, USA (PST)
Yes, we're traveling together,
but to different destinations.
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andrel wrote:
> On 30-3-2010 0:30, Darren New wrote:
>> How about the fact that the stars of the universe are all red-shifted
>> the farther they get from *us*? Or the fact that we seem to be the only
>> creatures in the entire *universe* that broadcast radio signals?
>
> For the latter see the Drake equation.
Or: http://xkcd.com/718/
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andrel wrote:
> On 30-3-2010 18:11, Darren New wrote:
>> andrel wrote:
>>>> How about the fact that the stars of the universe are all red-shifted
>>>> the farther they get from *us*? Or the fact that we seem to be the
>>>> only creatures in the entire *universe* that broadcast radio signals?
>>>
>>> For the latter see the Drake equation.
>>
>> I'm familiar with it. What about it?
>
> All we know that there are no radio signals broadcasted from a place
> exactly the right time ago to be just reaching us now, send towards us,
> and in a format that we recognize. Which is quite a long way away from a
> conclusion that no signals are send at all.
I keep wondering... Is humanity *constantly* broadcasting radio signals in a
simple format to nearby solar systems? What if aliens have a program exactly
like SETI@Home, trying to find intelligence in noise from received radio
signals, but neither party is sending anything?
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On 31-3-2010 4:40, Nicolas Alvarez wrote:
> andrel wrote:
>> On 30-3-2010 18:11, Darren New wrote:
>>> andrel wrote:
>>>>> How about the fact that the stars of the universe are all red-shifted
>>>>> the farther they get from *us*? Or the fact that we seem to be the
>>>>> only creatures in the entire *universe* that broadcast radio signals?
>>>> For the latter see the Drake equation.
>>> I'm familiar with it. What about it?
>> All we know that there are no radio signals broadcasted from a place
>> exactly the right time ago to be just reaching us now, send towards us,
>> and in a format that we recognize. Which is quite a long way away from a
>> conclusion that no signals are send at all.
>
> I keep wondering... Is humanity *constantly* broadcasting radio signals in a
> simple format to nearby solar systems? What if aliens have a program exactly
> like SETI@Home, trying to find intelligence in noise from received radio
> signals, but neither party is sending anything?
The major things we have been sending is FM (and AM) modulated radio and
TV. This is effectively a big signal in a very small bandwidth. If you
make a spectrum it will turn up as an unexpected peak above the
background. If you then become interested and look closer you will see
that the spectral contend is not compatible with a line originating from
an exited atom or molecule. So, if these aliens are at the right time
and place and have a SETI project running they will detect us in a
couple of centuries when the signal reaches them.
If they are listening but expect a different modulation scheme they
might just skip the lucille ball show as a strange artifact.
ATM AFAIK nobody is sending a deliberately simple encoded message. I
think the jury is not out on the question if that would be a good idea
at all.
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> The major things we have been sending is FM (and AM) modulated radio and
> TV. This is effectively a big signal in a very small bandwidth. If you
> make a spectrum it will turn up as an unexpected peak above the
> background. If you then become interested and look closer you will see
> that the spectral contend is not compatible with a line originating from
> an exited atom or molecule. So, if these aliens are at the right time and
> place and have a SETI project running they will detect us in a couple of
> centuries when the signal reaches them.
OOC how sensitive is the SETI equipment and project? I mean how big must a
signal be from 200 ly away that we are able to detect it with that system?
Extrapolating from the Voyager power levels and distance, I make it that we
need a 350 GW signal to be transmitted from 200 ly away. Is that realistic
to expect?
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And lo On Mon, 29 Mar 2010 18:17:10 +0200, Darren New <dne### [at] san rrcom>
did spake thusly:
> Phil Cook v2 wrote:
>> Depends on the setup. Off the top of my head imagine a situation with a
>> night-guard on reception. The building is locked, but the alarms aren't
>> on. Now if the building can't be locked without the alarms being
>> activated that's a pointless function of the card.
>
> Yes, but that's not the problem. Indeed, that's how it works now.
>
> The problem is that the card unlocks the door but does *not* turn off
> the alarm.
Yes I would consider that a flaw :-)
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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On 1-4-2010 8:56, scott wrote:
>> The major things we have been sending is FM (and AM) modulated radio
>> and TV. This is effectively a big signal in a very small bandwidth. If
>> you make a spectrum it will turn up as an unexpected peak above the
>> background. If you then become interested and look closer you will see
>> that the spectral contend is not compatible with a line originating
>> from an exited atom or molecule. So, if these aliens are at the right
>> time and place and have a SETI project running they will detect us in
>> a couple of centuries when the signal reaches them.
>
> OOC how sensitive is the SETI equipment and project? I mean how big
> must a signal be from 200 ly away that we are able to detect it with
> that system?
I don't know.
> Extrapolating from the Voyager power levels and distance, I
> make it that we need a 350 GW signal to be transmitted from 200 ly
> away.
The SETI equipment might even be somewhat more sensitive because they
are using larger disks. Then again they don't know what exact frequency
to tune into.
BTW I arrive at something more like 47 MW if the voyager is transmitting
all its power, which is unlikely, so the number could even be much lower.
> Is that realistic to expect?
If you really want to broadcast a message anything is realistic.
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andrel wrote:
>> Is that realistic to expect?
>
> If you really want to broadcast a message anything is realistic.
And what if they aim the message directly at us? I assume they can use less
power if they are pointing exactly at the Earth.
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scott wrote:
> OOC how sensitive is the SETI equipment and project? I mean how big must
> a signal be from 200 ly away that we are able to detect it with that
> system? Extrapolating from the Voyager power levels and distance, I make
> it that we
> need a 350 GW signal to be transmitted from 200 ly away. Is that
> realistic to expect?
Eric Korpela, one of SETI@Home admins, replies:
> SETI@home has a sensitivity of about 1e-25 W/m^2, so if I'm doing my math
> right, a transmitter at 200 ly would need to be about 7e+12 W EIRP
> (effective isotropic radiated power). If the transmitter was attached to a
> telescope the size of AO, it would have a gain of about 2 million, so the
> actual transmitter would need to be about 3.5 MW total power.
>
> Of course for a directional transmitter ET would need to suspect we are
> here.
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And more info:
Eric Korpela wrote:
> Nicolas Alvarez wrote:
>> Eric Korpela wrote:
>>> SETI@home has a sensitivity of about 1e-25 W/m^2, so if I'm doing my
>>> math right, a transmitter at 200 ly would need to be about 7e+12 W EIRP
>>> (effective isotropic radiated power). If the transmitter was attached to
>>> a telescope the size of AO, it would have a gain of about 2 million, so
>>> the actual transmitter would need to be about 3.5 MW total power.
>>>
>>> Of course for a directional transmitter ET would need to suspect we are
>>> here.
>>
>> What if it's not directional but broadcast? How much power do the
>> 200ly-far aliens need to send a radio signal covering an entire
>> hemisphere*, so that a reasonable amount still reaches us (or rather
>> SETI's antenna)?
>
> That would be 7 TW. Which is the amount of power you can generate with a
> solar array 150 km x 150 km* in size (assuming 24% efficiency). That would
> be a bit more than our society could afford to spend on trying to
> broadcast our position.
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