4 ms·
"...there is an ever-expanding bubble announcing Humanity’s presence to anyone listening in the Milky Way." This 200ly sphere does not equal detectable radio s
by robotomir 16y ago
"...there is an ever-expanding bubble announcing Humanity’s presence to anyone listening in the Milky Way."
This 200ly sphere does not equal detectable radio signals from Earth. SETI is looking for radio signals from the stars, yes, but they are looking for a focused and high-energy attempt from ETs to contact someone by beaming at specific stars. Radio "leaked" from regular transmissions typically does not carry a signal over interstellar distances.
- spiralganglion 16y agoThat's something I want to know. With the amount of energy given to our broadcasts, they surely would decay long before traveling any noteworthy distance. I'm curious as to what our most powerful broadcasts have been, and how far they'd travel before becoming unnoticeable. Especially, when compared to the amount of EMR released by neutron stars, pulsars, background noise, etcetera.
- robotomir 16y agoFrom the SETI FAQ: "Detection of broadband signals from Earth such as AM radio, FM radio, and television picture and sound would be extremely difficult even at a fraction of a light-year distant from the Sun. For example, a TV picture having 5 MHz of bandwidth and 5 MWatts of power could not be detected beyond the solar system even with a radio telescope with 100 times the sensitivity of the 305 meter diameter Arecibo telescope." Now, the Arecibo message should carry over a couple of hundred light years easily, but it was transmitted for three minutes only, and if you miss it, you miss it.
- meric 16y agoNot if you have faster-than-light travel! If they don't, it would seem pointless to contact aliens, by the time they send their ambassador on a multi-generational ship to Earth we humans may have already been extinct.
- btipling 16y agoFTL is probably not ever possible no matter how technologically advanced a society may be as it would allow for the violation of causality.
- ceejayoz 16y agoYou're assuming we already know everything there is to know about causality. It wasn't long ago that some people thought the sound barrier was insurmountable, or that trains would kill their occupants by going too fast.
- AngryParsley 16y agoFTL is equivalent to time travel into the past. If you have one you have the other. People thought humans wouldn't break the sound barrier for engineering reasons, not because the laws of physics prevented it. And just because people in the past thought something was impossible doesn't mean it will one day be possible. 100 years ago, physicists thought perpetual motion machines were impossible.
- jerf 16y ago"100 years ago, physicists thought perpetual motion machines were impossible." Bad example, man, the "anything is possible" crowd hasn't necessarily conceded that point either....
- khafra 16y agoThanks for saying what I wanted to. Everybody who knows nothing about physics always brings up the "humans can't possibly travel faster than 25mph" thing when someone who does know talks about violating causality, but as far as I've seen it was only printed in a newspaper or two, not espoused by physicists. The speed of light limitation is a necessary part of one of the most precise and thoroughly tested theories of all time.
- robryan 16y agoWhat about the bending of space for an instant travel time? That's more of an unknown in terms of possibility from what I have read.
- mchouza 16y agoThere is an analysis of the detectability of human radio signals at: http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html The main uncertainty is at estimating the level of radio technology that can be available to alien civilizations.
- ceejayoz 16y agoNot to mention whether they'd even bother with radio, if better technologies become available.