Science is one of the greatest achievements of humankind, and yet when our theories are confronted with reality, they often turn out to be coarse approximations. In astronomy in particular, this leads to a race between theory and observations, and often we discover things that seem to challenge everything we know.
As a case in point, here are some excellent examples of phenomena that really make researchers scratch their heads.
The Big Bang theory is one of the most successful theories of the 20th century. It is supported by plenty of observational evidence, and yet there are still a few kinks to iron out. One is called the "horizon problem", which tells us that the universe is too uniform. It’s the same everywhere.
If we look at two opposite points of the universe (so we can see them, but they can't see each other), we see that – using the temperature map of the universe known as the cosmic microwave background – every region is weirdly the same temperature. So how could they all be at the same temperature if these regions never touched? According to thermodynamics, this means at some point they should have been in contact.
An explanation for this is that they did touch. The universe must have been a lot more closely packed than we originally thought. If this is the case, then we need a mechanism to make the expansion happen faster at the very beginning. Otherwise, we just can't explain the current size. The solution for all these problems is called "cosmic inflation", but we are yet to confirm that it truly happened.
KIC 8462852, or Tabby’s star, has been described as the most mysterious star in the galaxy – and for good reason. Its light variation is absolutely unpredictable and is like nothing we have ever seen before. Over 1,600 days of observations, the amount of starlight appeared to dip by up to 20 percent on several occasions and at random intervals. This is not easily explained by a standard orbiting planet or that it is a variable star. There are also indications that the star might be experiencing a constant dimming, which is weird to say the least.
Explanations range from serious ones, like a ringed planet or comets blocking the light, to more facetious ones like a megastructure surrounding it. While both the comets and megastructure ideas have been discarded, we still haven't uncovered the cause of this flickering.