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Old December 18th 18, 06:05 AM posted to sci.astro
Thomas 'PointedEars' Lahn
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Posts: 76
Default No Alien Visits Ever

wrote:
A very good reason why we're never visited by any aliens :


Already discussed and refuted.

Distances between stars are way too great, as to preclude any
possibility of practical travel between them. Like everything, Aliens
would be limited to the accepted and proven speed limit of
c = 3E8 m/sec,


It is c = 1/√(ε₀ ε_r) = 299'792'458 m/s (exact) instead.

[“sec” is not a proper abbreviation in the SI, which defines c.]

https://www.bipm.org/en/publications/si-brochure/

But that is only the *local* speed limit for objects with *real* mass.

[It is has been stated, and I have proved independently, that objects
with imaginary mass would have to move at v c: v = √(1 − m²c⁴/E²)
according to special relativity. However, the suggestion of equivalent
imaginary energy which would kill this idea gives me pause as of yet.]

But:

“Space can do whatever the hell it wants.”

—Lawrence M. Krauss, theoretical physicist and cosmologist

General relativity permits an Alcubierre-style warp drive that would allow
us to travel much faster. You only have to find some negative energy to
expand space behind you

Consider that space in a black hole is falling faster than c:

http://jila.colorado.edu/~ajsh/insidebh/waterfall.html

And space is already expanding faster than c beyond ca. 14 Gly away (and
that is assuming a *constant* Hubble parameter, which is not so – the
expansion is accelerated):

v_rec = H₀ D,

with H₀ ≈ (70 km/s)/Mpc and D the proper distance.

We have no theory of quantum gravity yet, so there might be stable wormholes.

We understand only ca. 5 % (baryonic matter) of the energy content of our
universe *quite* well (not completely: e.g., neutrinos apparently have
non-zero mass and should not have according to the standard model) – who
knows what other possibilities there are?

and practically and likely something FAR slower.


Using conventional means, yes. Project “Breakthrough Starshot” aims at
0.15 c to Proxima Centauri (for the probe the journey takes about 27.6 years
then, see below), but those are only starchips[tm].

http://breakthroughinitiatives.org/challenges/3

And BTW, Proxima Centauri b is the closest Earth-like planet that we have
found yet (in 2016), only 4.2 ly away. There might be extra-terrestrials
there, and they could be here within years (or faster, see above).

Distance = Speed x Time. Do the simple math.


It is not that simple. You are applying special relativity incompletely
(and therefore inconsistently):

If you travel at v towards an object for an observer at rest to that object,
then that object travels at −v relative to you, and those *moving* distances
to those objects are length-contracted for you by the Lorentz factor

γ(v) = 1/√(1 − (−v)²/c²) = 1/√(1 − v²/c²).

In this way, you can reach the center of the Milky Way (ca. 25'618 ly ≈ 7855
pc away) *within* your human lifetime *without* cryogenics (you do NOT have
to wait more than 25'618 years before you arrive).

Fuel problems aside, the only problem left is time dilation: When you return
this way, nobody whom you knew would be alive (for them, there is no length
contraction, but there is time dilation, and it took you twenty million
years to come back), and human civilization may be long gone. So it would
still be a one-way trip in that sense.

Do the not-so-simple math

Probably just as well. If Man is any example, then aliens who would
likely be more advanced, and would view Mankind as a primitive entity
to be used at will. We might make delicious hors d'oeuvres !


A distinct possibility, but not the only one. Consider where human
civilization could be if it had progressed from the ancient civilizations,
without the (probably unintentional but still careless) burning of the
Library of Alexandria by the Romans under Julius Caesar, without
the Dark Ages, the Inquisition, all the small wars and the two World Wars.

--
PointedEars

Twitter: @PointedEars2
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