First let me say that my reasoning is based on the Bible, so if you don't believe in the Bible then it is pointless arguing over this subject. What I would encourage you to do is first look at the creation studies and come to a realization that we are not an accident of nature but a well thought out and wonderfully designed creation by a supreme God.

There is no indication in the Bible that God created any other beings like mankind. That is to say we are the only creatures with a Soul and a Spirit. Genesis 2:7 separates us from the animals on the earth and the Angels in heaven

7.And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.

Animals do not have a soul, Christ did not die that animals could have eternal life, they are instinctive creatures and do not posses a free will, independent and cognitive thought. They may not be dumb but neither are they equal in any respect to mankind.

It is also well to note that if God had created another creature similar to man then why did Lucifer, Satan, the Devil pick on mankind to vent his anger. If we were created with a free will to choose between right and wrong then surely they too would have been given this attribute, and like Adam and Eve eventually strayed from the path. If this is the case then we come into serious theological discussion on how many times can Christ enter a world and die, even if it is another life form.

We must also take into account that God created man for a reason, it was to look after the Garden, which was placed on the earth for a reason also. Genesis 2:15

15. And the LORD God took the man, and put him into the garden of Eden to dress it and to keep it.

Added to this is the fact that God created man in HIS image (Genesis 2:27), would He not do the same if He created any other creature. Why make them inferior, if you are going to create something surely God would do it right first time.

27. So God created man in his own image, in the image of God created he him; male and female created he them.

This is all well and good and what I am saying really speaks to the converted. After all if you believe in aliens then you could make any hypothesis and in reality as the Bible does not say otherwise than you could say yes they might exist. All I have put forward is an idea based on common sense logic. If this is the case and there aren't any aliens, then what are these strange occurrences we keep hearing about?

Unidentified Flying Objects as the name suggests are unidentified, and not necessarily alien in origin, however people have had close encounters with craft of unusual description and flying characteristics. Most of these can be accounted for by military aircraft and technology. We know from documents found after WWII that the Germans were producing and developing weapons and aircraft far in advance of anything seen on the earth. After all they had kidnapped or acquired many scientists to work on their projects. It was after the war when the U.S and Russia stepped in and re-acquired these scientists to work for them, whisking them away with anything that was left intact at these development bases.

It was later in 1947 when we got the first glimpse of their efforts from the now famous Area 51, and the Roswell incident. Just think then, the developments which would have been made from then until now. Most of the aircraft we are privy too from these sites are the spin off's, the by-products of the real development. If you are talking about anti-gravity you must look back to the late 1800's for the development of that. We are not talking new technology, just hidden technology, saved for military purposes.

Next we have the Satanic element. We know from the Bible in Ephesians 2:2 that Satan is quite at home in the air and all about the earth.

Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience:

In fact he is the prince of the earth, a title taken from Adam when he sinned. If this were not the case then how could Satan have been able to offer then to Jesus in Mathew 4:8-9

8. Again, the devil taketh him up into an exceeding high mountain, and sheweth him all the kingdoms of the world, and the glory of them;
9. And saith unto him, All these things will I give thee, if thou wilt fall down and worship me.

This was no mere joke, Jesus did not contradict him and it would not have been a valid temptation anyway if it was an invalid proposal. But why would the evil spirit Satan or his angels pretend to be aliens?

This is a very good question and one, which has two answers. The first is to discredit the Bible and the Christian teachings. If he can get people preoccupied with extra-terrestrials then their minds will be far from God and the teachings of the Bible. Secondly he is preparing for the end and some great deception which he will try to cover up the rapture with and also probably introduce the Anti-Christ. Whatever his future plans you can be sure that he is reveling in the confusion being created.

Angels can manifest themselves in many forms and there is little to doubt the fact that Satan's angels are any different. Even though we call them Devils or demons they are in essence angels. Also it is a misconception to think that they are locked away until the end of time, yes some are the ones which sinned and mated with human women as told in Genesis 6:4. They are as free as Satan himself and doing his bidding as we speak. Just because they have lost their 'position' in heaven, it does not mean they have lost any of their basic powers of an angel. Although it is the Word from God, which the angel takes to do His bidding that gives the angel the ability to do a task, there are inherent abilities already in the angel that God can utilize. After all many angels do day to day tasks, for which God would have equipped them from first creating them.

Angels are in some way similar to the animals of the earth, they all have jobs to do in the grand make up of things and they all have specific roles and abilities to do those roles. If you take them from their environment, this does not mean they loose that ability, it just means they can no longer do that specific role to which they were created. So Satan has an army of angels all with different abilities and I am sure he uses them wisely.

The last point I would like to make is probably the most disturbing answer to alien existence. It is the union between man and the demonic forces. Most World powers have dabbled with the occult, the Russian and Americans being the most prominent. Even today they experiment with powers they should be leaving alone, trying to produce a perfect weapon or spying device. They have literally sold their souls to the Devil for a dream. I am sure that Satan has connections high up in governments, and controls many politicians, in return helping scientists develop better aircraft and weapons, putting into their minds the blueprint for HIS future.

The rest is down to us, our imagination. If you think you see something long enough then eventually you will see it. Fear is a terrible weapon and one, which Satan has, had plenty of practice. There is a time coming when all these things will make sense and Satan will show his true colors. Unfortunately that time will be during the period of tribulation, as foretold in the Bible. The only way to escape it is to believe in God and follow Him, not the way of the world. Luke 21:36 says;

36. Watch ye therefore, and pray always, that ye may be accounted worthy to escape all these things that shall come to pass, and to stand before the Son of man.