"BradGuth" <bradguth@gmail.com> wrote in message 
news:784c9cff-d39b-4819-b232-6d681229e6b0@j9g2000prh.googlegroups.com...
On Aug 29, 1:43 pm, "HVAC" <harlowcampb...@gmail.com> wrote:

"Chris.B" <chri...@mail.dk> wrote in message

news:36806e20-6abd-42c0-b12a-b031878f7d59@33g2000vbe.googlegroups.com...
It is not unlikely that advanced alien races could easily cloak their
presence from us either optically or by mass psychological masking. I
am not suggesting they are doing so but it is not impossible. This
might explain the troubling differences in opinion regarding the exact
details of sightings of UFOs by experienced multiple witnesses when
the masking/cloaking/forced-amnesia system (supposedly) breaks
down. :-)

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Putting your kookiness aside for a minute, consider this:

ANY craft traveling past say 50% light speed would be
visible across 1/2 the galaxy at least. The X-ray emissions
alone would mark it as an alien craft.

Where are the trails?

ET spacecraft are likely not that inefficient, although our Selene/
moon leaves a 900,000 km trail of sodium as is.  Better detection of
sodium might get that worth showing easily over a million km of a
trail.

Electrostatic and magnetic forms of propulsion might go undetected
unless the ET spacecraft were cloaked like somewhat of a black hole.
A purely gravity formulated thruster/puller might be entirely stealth.

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Do you have to blow up your "gravity formulated thruster/puller"
every night, or do you keep it inflated all the time ??