Those are all interesting possibilities to theorize about. We can't be certain about any of them, however. The thing that makes me pretty confident that aliens are visiting us in spite of these various theories as to why they shouldn't be able to is the sheer weight of incidents and very credible witnesses that one finds if one bothers to seriously investigate the issue...rather than just stating an established belief that is based upon convention, habit, and faith.

Oh, and the other thing is: direct personal experience. I have seen craft in the sky which could only have been 1 of 2 things:

1. alien vehicles of an advanced technology that is way beyond ours.

or...

2. secret vehicles made by our own government utilizing a technology utterly beyond anything they're telling us about...and then flown rather recklessly over areas easily visible to the ordinary public, without apparently having any worries over "breach of security" in so doing.

The former case seems far more likely to me than the latter. But it could have been either, I suppose. If it was the latter case, then the government must want to trick us into believing that there are alien vehicles visiting here, while simultaneously denying that there are! And that again seems quite unlikely to me. ;-D I think it far more likely that they don't want us to know that there's something out there far more advanced than them, and that they can't do anything about it. The government does NOT like appearing weak or helpless to deal with something...and they DO like keeping various matters top secret, for their OWN protection and control of the situation.