Posted by prossercj 2 days ago
It's got no known abiotic process for being generated, but a clearly understood connection to life, and is apparently very reactive and would have to be actively re-generated at mass scale to sustainably show up in an atmosphere.
Nothing should be taken as proven, but it feels staggeringly plausible, and in my opinion would be the biggest of the "big if true" space stories I've ever seen in my lifetime.
At one point in this fascinating talk, she mentions that aliens would immediately be able to identify Earth as inhabited by life, because only a stupid and yet advanced civilization would be capable of creating CFCs. I highly recommend this video.
So I think not many generations would be necessary, given individuals with 83% the average size or smaller are a common occurrence. The trait small body size should just become more common.
Let's simplify the problem (take a spherical cow in the vacuum), say we have planets A and B, 100 LY away from each other, time flows at exactly the same rate near both, clear path in between them, they move through space at the same speed and relative direction, etc.
I'm on planet A. I send out a signal towards planet B. I jump to planet B and wait 100 years. I observe the signal.
Now my simplistic assumptions probably suggest that this isn't that much different from sending out a carrier pigeon while I take the train to its destination and wait. Very obviously I'm not Einstein. What am I missing?
Ship 1 FTL jumps, transmits message to Ship 2 that is moving relativistically, and then Ship 2 FTL jumps back. Ship 2 can arrive before Ship 1 left, creating a paradox if they give them the message.
This assumes that FTL follows relativity where physics are the same in all frames. If it happens in fixed frame, then there isn't a problem. But that would break physics; I guess FTL would break physics too. We would either need to give up on causality and except weird things happen, or give up on FTL and accept light speed as the speed limit.
I think the basic idea is that when two people are experiencing time dilation, FTL communication makes it possible (according to relativity equations) for a recipient to receive a message, reply to it, and have the original sender receive the reply before the point in time (in the original sender’s point of reference) the original sender sent the initial message, which clearly violates causality.
I think your scenario would not break causality because you are assuming both A and B are experiencing time at the same pace, so there would be no way to take advantage of time dilation.
Hm, that’s probably not a very clear explanation..
Ok, suppose you depict time and one dimension of space on a grid, where traveling at c is depicted with a line that makes a 45 degree angle with the space axis. Draw two such lines crossing at the t=0, x=0 point. If you apply a “hyperbolic rotation” aka a “boost”, keeping the origin fixed, these lines will stay fixed, and each point in one of the 4 quadrants made by these lines will remain in that quadrant.
The upper quadrant consists of all events in the absolute future of the event at t=0, x=0 . The bottom quadrant consists of all events in the absolute past of the event at t=0, x=0 .
These boosts are what happens when one changes one’s reference frame by changing velocity. Of course, changing one’s velocity cannot change what events can have a causal effect on what other events, as it only changes one’s perspective.
Any line segment that you draw that would be faster than light speed can be hyperbolically rotated so that the endpoint has an earlier time coordinate in the boosted frame than the start point.
Whereas, the points in the upper quadrant always have positive time coordinates.
Now, if you only allowed one instance of FTL ever, that might not cause any cycles in causation? Maybe even if you only allow it in one direction? But those don’t seem particularly plausible. If you have it in both directions, and they aren’t separated enough I guess, then one could combine those line segments with ones that go at 45 degrees (I.e. light speed) in the forward-in-time direction, to make a loop.
Uh.
Ok so specifically these hyperbolic rotations, in units where c=1 , are t’ = t cosh(theta) - x sinh(theta) and x’ = x cosh(theta) - t sinh(theta)
Uhh…
Ok I think if FTL was only possible if the signals are still forward in time with respect to one fixed preferred reference frame, then there’s no issue. It is just when it is possible in both directions in a variety of reference frames that it results in a loop.
In the meantime, we continue to develop new designs for deep space mobile habitats and the expedition can have the newest design to build a couple in their new system.
I imagine a culture that has developed in a deep space habitat would not feel life on a planetary surface very appealing.
You can filter by cycle & purpose - I think you want GO 4 then look at Exoplanet Atmospheres and Habitability?
Related, but here is the Spectra of K2-18 image - https://webbtelescope.org/contents/media/images/2023/139/01H...
> Gases found are the same as those produced by algae on Earth
AIUI, the sensors used for this discover don't look for just _one_ gas, but as many as possible. So Oxygen is probably included in that list.
Life needs more than just oxygen gas in the atmosphere to thrive. The right combination of gasses is a better signal that life could be there versus just the presence of one gas.