平行宇宙理论最常见的批评是缺乏通过观察和实验收集的经验证据得出的科学事实。由于许多原因，已经证明很难获得关于交替现实存在的科学证据，其中一个原因是，通过观察现实，我们也在改变它。著名的双缝实验(Live Science, 2012)证明了这一迷人的概念。本实验从本质上证明了能量和物质表现出粒子和波的特性，说明了量子力学的基本概率性质。在一个基本的双缝实验中，我们观察到一束激光射向有两个平行缝的薄板。光的波状性质导致光波通过两个狭缝时相互干扰。当从板块后面观察时，我们可以看到亮带和暗带正在形成，如果我们假设光只由粒子组成，这是出乎意料的。而不是像粒子，光被吸收在屏幕上，就好像它是由光子或离散粒子组成的(Live Science, 2012)。这个神秘的实验结果导致了对单个光子固有概率性质的检测。当德银(2001)进行他版本的双缝实验时，他进一步研究了这些发现。他说，当我们看到一个光子穿过一个狭缝时，平行宇宙可能会看到一个光子穿过另一个狭缝。根据Deutsche(2001)，我们的宇宙是我们观察到的有形粒子的现实，而影子粒子的现实实际上是一个平行的宇宙。
The most common criticism of the parallel universe theory is the lack of scientific facts derived from empirical evidence collected by means of observation and experiments. It has proven difficult to acquire scientific proof for the existence of alternate realities for many reasons, one of these reasons being that by observing reality, we are also altering it. This fascinating notion is demonstrated by the famous Double-Slit Experiment (Live Science, 2012). Essentially, this experiment proves that energy and matter display characteristics of particles and waves, indicating the fundamental probabilistic nature of quantum mechanics. In a basic Double-Slit Experiment, we observe the light of a laser beam aimed towards a thin plate pierced with two parallel slits. The wave-like nature of the light results in the light waves interfering with each other while passing through the two slits. When observed from behind the plate, one sees bright and dark bands being created, which is unexpected if one were to assume that light only consisted of particles. Instead of acting like particles, the light becomes absorbed on the screen as if it consisted of photons or discrete particles (Live Science, 2012). The mysterious result of this experiment lead to the detection of the inherent probabilistic nature of individual photons.When Deutsche (2001) conducted his version of the Double-Slit Experiment, he took the findings even further. He states that when we perceive a photon passing through one slit, a parallel universe might perceive a photon passing through another slit. According to Deutsche (2001), our universe is the reality of the tangible particles that we observe whereas the reality of the shadow particles is actually a parallel universe.