# How do we know that the universe is three dimensional?

1. Jan 8, 2016

### Fiziqs

When we look at the world around us our minds create a three dimensional representation of the world based upon our sensory input, but how do we know that there aren't in fact more dimensions from which we either receive no sensory input, or from which we receive input, but our brains and our mathematics have evolved to interpret three dimensionally? Or perhaps there are only two dimensions, from which our minds extrapolate three dimensions. Or taken to the extreme, how do we know that there are any actual dimensions at all?

How do we know that what we see and interpret as being three dimensional, actually is?

2. Jan 8, 2016

### davenn

think about the difference between a 2 dimensional photo of a room and the real 3 dimensionality of that room
think about what you can and cannot do in the photo Vs in the actual room

consider depth of field implied and real

3. Jan 8, 2016

### Staff: Mentor

And consider parallax.

4. Jan 8, 2016

### Khashishi

If you follow any popular modern science, you'll hear about how string theory predicts 10 or more space dimensions, and we can't see these dimensions because they are small and curled up. But there's no evidence for extra dimensions and there's plenty of evidence for 3 (space) dimensions.
On the other hand, you'll hear about holographic theory which suggests that there might only be two dimensions, but none of the details are worked out, so it can't really be called a theory.
Ultimately, science is about experiment, and all our experiences seem to show us a 3D universe, so unless we can come up with better experiments which show the contrary, we should go along with the preponderance of evidence and our intuition and simply accept 3D. "know" is too strong a word here.

5. Jan 8, 2016

### Staff: Mentor

Are holograms necessarily 2D? I can envision interference patterns in higher dimessions.

6. Jan 8, 2016

### sophiecentaur

In fact, all (near field) interference patterns are 3D. It's just that we normally observe them by putting a screen (2D) in the way.
The interference pattern that's produced by an rf transmitting array over a hilly terrain is demonstrably 3D because the maxes and mins vary as the receiver is moved in 3D. It would be possible to have a photographic or electronic light sensing array that extends in 3D as long as the receptor cells were very small.