# What were the dimensions of the universe during Planck epoch?

Wikipedia says:

It is believed that, due to the extraordinarily small scale of the universe at the time, quantum effects of gravity dominated physical interactions.

But I wonder whether there is any indication that the dimensions of the universe were small at the time rather than being infinite?

Undoubtedly it was very dense but very dense does not necessary mean "small".

Is Wikipedia wrong on this point?

• Comment to the question (v1): It seems that OP is essentially pondering if the volume of 3-dimensional space is infinite or finite. Related: physics.stackexchange.com/q/9419/2451 and links therein. – Qmechanic Dec 20 '13 at 13:58
• The (visible) universe is currently approximately $10^{27}$ m in diameter. From supernova surveys, we know that the universe is accelerating its expansion. Extrapolate backwards for about 13.8 billion years and you get a diameter that is infinitesimal. – Kyle Kanos Dec 20 '13 at 14:01
• Saying that the scale was small doesn't necessarily imply that the spatial dimensions themselves of the whole universe were small. IMHO, that sentence from Wikipedia would be better if it used the term "scale factor". On a related note, see physics.stackexchange.com/a/136861/123208 – PM 2Ring Oct 19 '20 at 23:48

• @Anixx I am confused by "approaching de Sitter space". A 3D boundary to a 4D sphere is a de Sitter space. It is a solution of the Friedman equation with $\Omega_\Lambda=0$ and $\Omega_m>1$. It never approaches a de Sittrer space because it is always a de Sitter space. – Buzz Oct 30 '20 at 22:22