The Mathematical Universe Hypothesis (2007)
This is one of the oldest concepts in Ancient Philosophy.  Not only did the Pythagoreans famously believe it, they also derived a number of other concepts from it, including Eternal Return:<p>&quot;The Pythagoreans too used to say that numerically the same things occur again and again. It is worth setting down a passage from the third book of Eudemus&#x27; Physics in which he paraphrases their views:<p>&gt; ‘One might wonder-whether or not the same time recurs as some say it does. Now we call things &#x27;the same&#x27; in different ways: things the same in kind plainly recur - e.g. summer and winter and the other seasons and periods; again, motions recur the same in kind - for the sun completes the solstices and the equinoxes and the other movements; But if we are to believe the Pythagoreans and hold that things the same in number recur - that you will be sitting here and I shall talk to you, holding this stick, and so on for everything else - then it is plausible that the same time too recurs.’&quot;<p>- Simplicius 
Commentary on the Physics 732.23-33.&quot;<p>The notion of a mathematical universe was also quite famous with Platonists and Neoplatonists, who debated it over centuries.  There was a form of Platonic revival -- which might owe something to Spinoza and Newton -- in the Early Modern period.<p>In the 20th century, Konrad Zuse&#x27;s &quot;Digital Physics&quot; is explicitly a Mathematical Universe Hypothesis.<p>The way people attribute the concept to Tegmark is somewhat laughable, IMO.  He just modernized small slices of it, in a rather haphazard way.