Why are the Voyager probes slowing down more than expected?
So many people, myself included, wanted this anomaly to be the proof that something was highly wrong with the numbers. It pisses me off when Einstein's theories are thought to be wrong based on observation and then it turns out to be some bullshit reason that proves he was right all over again. I have nothing against Einstein. If he is right, we are never going to reach the stars in my opinion. So many people disagree. I just don't think it is going to happen without some completely new idea of what the universe is made of coming about.
The nuclear pigs (mini nuclear power plants) on both probes are mounted on the side of the space craft opposite Earth. This is because the pig would interfere with transmissions back to Earth. This means the back side of the big antenna (think satellite dish) aimed at Earth acts as a reflector for the heat radiation from the pig. The radiation is radiated out in all directions. Some of this hits the back of the antenna. The bouncing light does not completely cancel out. There is just a bit of advantage coming off of the back of the antenna. This means the space craft is slowing down because of uneven heat distribution from the pig.
This idea has been kicked around for a long time, but someone finally sat down and did the numbers.