Nature

==Matter and energy==
[[File:Hydrogen Density Plots.png|thumb|The first few [[hydrogen atom]] [[Atomic orbital|electron orbitals]] shown as cross-sections with color-coded probability density]]
{{Main|Matter|Energy}}
Some fields of science see nature as matter in motion, obeying certain laws of nature which science seeks to understand. For this reason the most fundamental science is generally understood to be "[[physics]]"—the name for which is still recognizable as meaning that it is the "''study of nature''".

Matter is commonly defined as the substance of which physical objects are composed. It constitutes the [[observable universe]]. The visible components of the universe are now believed to compose only 4.9 percent of the total mass. The remainder is believed to consist of 26.8 percent [[cold dark matter]] and 68.3 percent [[dark energy]].<ref name="planck_overview">{{cite journal |title=Planck 2013 results. I. Overview of products and scientific results – Table 9. |journal=[[Astronomy and Astrophysics]] |first1=P. A. R. |last1=Ade |first2=N. |last2=Aghanim |author2-link=Nabila Aghanim|first3=C. |last3=Armitage-Caplan |last4=et al. (Planck Collaboration) |date=March 22, 2013 |arxiv=1303.5062|bibcode = 2014A&A...571A...1P |doi=10.1051/0004-6361/201321529 |volume=571 |pages=A1|s2cid=218716838 }}</ref> The exact arrangement of these components is still unknown and is under intensive investigation by physicists.

The behaviour of matter and energy throughout the observable universe appears to follow well-defined [[physical law]]s. These laws have been employed to produce [[Physical cosmology|cosmological]] models that successfully explain the structure and the evolution of the universe we can observe. The mathematical expressions of the laws of physics employ a set of twenty [[physical constant]]s<ref>{{cite web|last = Taylor|first = Barry N.|date = 1971|url = http://www.physics.nist.gov/cuu/Constants/introduction.html|title = Introduction to the constants for nonexperts|publisher = National Institute of Standards and Technology|access-date = January 7, 2007|archive-url = https://web.archive.org/web/20070107012004/http://physics.nist.gov/cuu/Constants/introduction.html|archive-date = January 7, 2007|url-status = dead|df = mdy-all}}</ref> that appear to be static across the observable universe.<ref>{{cite journal|author=Varshalovich, D.A.|author2=Potekhin, A.Y.|author3=Ivanchik, A.V. |name-list-style=amp|title=Testing cosmological variability of fundamental constants|journal=AIP Conference Proceedings|date=2000|volume=506|page=503|arxiv=physics/0004062|doi=10.1063/1.1302777|bibcode=2000AIPC..506..503V|citeseerx=10.1.1.43.6877}}</ref> The values of these constants have been carefully measured, but the reason for their specific values remains a mystery.