Some theories predict the existence of higher dimensions. With sensitive gravitational experiments we can test that idea.
The Universe is Still Not a Hologram
New theoretical work on the holographic principle is interesting, but the universe is still not a hologram.
Radion Days
We usually think of efforts to unify Einstein’s theory of gravity with other forces as a more modern trend. Models such as string theory and loop quantum gravity are seen as modern ideas. But in fact, as soon as Einstein presented his model there were efforts to unify it with the other known force at the time, electromagnetism.
A Lack of Balance
Yesterday I wrote about the difficulty in understanding black holes. The heart of this difficulty lies in trying to understand how two radically different physical models (general relativity and quantum mechanics) might integrate into a single, unified model. Two major approaches to this problem are loop quantum gravity and string theory.
The 5th Dimension
From measurements of distant supernovae, we now know our universe is not only expanding, but that it is expanding at an ever increasing rate. This cosmic acceleration is driven by what we call dark energy. While we can see the effects of dark energy, and we know it makes up about 68% of our universe, we don’t really know what dark energy actually is. That means while the experimentalists scurry to get more data, the theorists work frantically to explain what’s going on.
Across the 8th Dimension
A few years ago a research team measured the force of gravity over very small distances. Their result places very stringent constraints on the space-time structure of our universe. Either the universe consists of only the four dimensions we see around us, or else all dimensions beyond those four must be very small, no more than about 10 microns, roughly one-tenth the width of a human hair. What, you might ask, does proving Newton right (yet again!) have to do with hyperdimensional physics? Quite a lot, it turns out.
It Goes to Eleven
String theory proposes that there may be 11 dimensions to the universe, where we only see space and time. We couldn’t see these extra dimensions directly, but if they are there we could observe their effect on gravity.