What are the 11 dimensions of M-theory in layman's terms?

Answer 1

4 of these dimensions are the regular ones most of us are familiar with; 3 of these are spatial dimensions: up-down, left-right and forwards-backwards. The fourth one is a time dimension.

In a 4 dimensional space you thus require four numbers to uniquely specify a certain location in space and time. A quick example would be the location of a meeting somewhere on Earth; you'd need four bits of information: the latitude and longitude of the location, the height and finally the time of the meeting.

In M-theory physicists assume there are 7 additional spatial dimensions. Thus in M-theory you would need a grand total of 11 numbers to uniquely specify a location in spacetime.

These additional 7 dimension are not equal to the regular 3 spatial dimensions in one important aspect; they are curled into small loops. This makes them periodic (if you walk in their direction you will after a while end up where you started), and they are very tiny. You can imagine them as small loops of additional space at every location in our regular 4 dimensional spacetime.

These loops cannot be seen however because they are so very tiny. If M-theory is correct we might be travelling in these dimensions all the time, but we don't notice it because they are so small.

A good analogy Briane Greene used is that of an ant on a garden hose. For the ant the garden hose seems 2 dimensional (3 if you count time); the ant can move forward and backwards on the hose, but it can also move around along the hose in a circular fashion. But if you stand some distance away the hose appears to be a line, a 1-dimensional object. You do not see the second curled-up dimension because it is too small because you are too far away.

In this way the extra dimensions M-theory requires are also hidden, but they might be spotted in modern particle collider experiments such as the LHC, since these can be used to probe the small distance scales where these additional dimensions might become important.

Answer 2

M-theory proposes that the universe has 11 dimensions - our familiar 3 dimensions of space, plus time, and 7 hidden dimensions. These extra dimensions are compactified or curled up, making them too small for us to detect directly, but they could influence how particles and forces behave. M-theory attempts to unify different versions of string theory by incorporating these extra dimensions.