e=mc² is a testing pack currently designed for Minecraft 1.12.2.
It is available on the Technic Launcher. The current release of e=mc² is version 1.5.4, released on Saturday, February 10, 2018.

Custom Sphax Patches (In Menu Loading Order, Top to Bottom)
Sphax PureBDcraft Modded Textures for e=mc² - February 10, 2018 for e=mc² 1.5.4+
Default
These patches are notorious for not working if e=mc² is allocated less than 10 GB of RAM.

Basic Prerequisites
Technic Launcher
Java Runtime Environment 8u162 x64 - Windows - macOS - Linux

If you wish to play around with the e=mc².zip file, here is the direct download link.

Vanilla Minecraft Packs Compatible with e=mc²
VoxelBox Scientific HD (1.6.1+) - superseded by NosLabs Custom Blocks mod
Original NosLabs Resource Pack (1.6.1+) - superseded by NosLabs Custom Blocks mod