Pure speculation that probably wouldn't hold up even in a simulation without a multitude of adjustable post hoc parameters. Any impact that could reverse the rotation would likely obliterate the planet. Sent from my VS995 using Grasscity Forum mobile app
For as much as I don't believe the big bang theory is the best explanation for our universe, opposite rotation doesn't disprove it. It isn't hard to imagine how it could happen. The most likely is that it happened when the planets first formed. If the majority of the materials that formed Earth and Venus were once one giant ball of lava, if an asteroid or comet impacted the ball, it could be split into 2 smaller pieces and the impact would send them in opposing rotations. Circling back to when the planets first formed, again, if there were a large ball of molten lava that was spinning faster than what it could contain.. if a section of it were to be ejected from centrifugal, it very well could gain an opposing rotation as it leaves the original mass of lava. Impacts are another possibility. As Norse said, an impact that would reverse a planet's rotation could very well destroy it.. there could be a succession of small impacts. If there was a large comet or asteroid or even another planet that crumbled, it's pieces could travel the same trajectory and if they were to collide with another object, it would be a series of small impacts. With enough chunks slamming a planet over and over, it could very well effect its rotation. I think the most obvious is that we just don't know enough yet. For all we know, there could be properties of the material that simply make it spin opposite of the way most material does. We can make magnets attract and repel and the sun and the planets are all doing their lil dance in magnetic fields. It could have physical properties that make it opposed that we are not aware of yet. Bottom line is, in no way, shape, or form does opposing rotation disprove the big bang theory. If it did, I'd be all up on that shit.. because I do dislike the big bang as an explanation for the universe.
Your toy is loosing momentum due to resistance from both the atmosphere around it and friction from where it touches the surface it rests on (gravity is only relevant in that its whats making demonstrating your spinning toy without contact to any other surface impractical) neither of these things apply to the rotation of planetary bodies.