Had an interesting thought:
The Rapture will occur in the "twinkling of an eye." That is faster than the time it takes to blink, faster than a synapse firing in the brain. To a secular person, you would be standing there, and before their brain could even register you disappeared, blamo, you are gone and already thousands of feet in the air.
Some say the trumpet may sound like thunder to a secular person, but I suspect they will hear nothing at all. Some say the thunder is the sonic boom of all the people shooting upwards suddenly at WELL over the speed of sound (in fact, if we travel up at the same speed we vanish, we will be at the highest cloud levels inside 2 seconds). Why do I think the secular will hear nothing? Because, at the instant we vanish, we are also transformed, no longer subject to earthly physics and able to pass through matter regadless of its density. Therefore, no sonic boom. The only hint I believe the secular will get is our clothing hitting the floor roughly .10 seconds after we vansih, since it will happen so fast, our clothes will hover in place for a split moment before gravity takes over.
Also, no camera on earth can record the moment we transform, unless perhaps it is a camera that can see past the visible light spectrum. Since we are transformed inside and out, a camera of that specification MAY be able to take a snapshot of the moment we are glorified, the moment we go from flesh and blood to transdimensional, meaning, impervious to matter and time (as we know it), and fit for eternal life in any level of the 3 Heavens. The power exuded from a sudden transformation like that could theoretically elicit a form of light energy visible to any photo device. If the secular were able to see the light emission from the moment of transformation, that would mean that the transformation is not 100% efficient and therefore imperfect, producing waste in the form of visible light. On the other side of this coin, one could say that since our new bodies are made alive and animated through the very Spirit of God, it MUST elicit some type of detectable radiation due to the sheer magnitude and surge of transformative power. The result, detectable particle radiation somewhere in the spectrum of light. Could a camera catch the explosion of energy coming from us the split fraction of a second before we vanish? Possibly, yes. However, there will most likely be colors in Heaven we don't even know exist yet, so even though the reaction may be detectable with current technology, perhaps not all of it will be, accounting for the colors on the spectrum in a range that we are not technologically advanced enough to see yet. Our eyes will be glorified in Heaven, meaning we will most likely be able to see the entire color spectrum. This will alow us to see colors we never knew existed.
Since God is perfect, and we will have bodies like Jesus, I suspect the transformation will completely defy all known laws of physics in its suddeness and power. Such an immediate transformation in genetic and biological structure would normally kill us instantly, but since God is who He is, it will happen in such a manner that is not only 100% efficient, but perfect and blindingly fast. Another way of saying that is the moment we are transformed will be so sudden and complete, we won't even know until it's already over, and we suddenly realize we are not the same (and simultaneously going up REALLY fast). This also serves another purpose, in that the moment we are pulled up, we will accelerate to a level of g forces that would normally leave our bodies in a state similar to a slurpee. Due to the speed of our glorification, we won't even realize we are traveling up until we are well into the sky.
Given these things, the moment of the Rapture will throw the left behind world into absolute madness, clamoring for an explanation. To us, the moment of the Rapture will be so fast and sudden, our first few moments in will be overwhelming in intensity. Imagine going from your everyday life to being not only immortal, but seeing and hearing things you can't even describe in words, ALL this within the first few seconds after glorification. Meanwhile on earth, the left behind are sitting in ther living rooms and walking down the street, etc. Those inside are shocked by a sudden series of loud exploding sounds and screaming as cars slam into each other at high speeds, driverless. Those outside look about them only to see random sets of clothing strewn out along the sidewalk every few yards. It will be a strange and terrifying day for the unbeliever. While the moment of the Rapture may be undetectable, the consequences will not.