The universe is expanding faster than the speed of light! This is one of the most profound discoveries in modern cosmology, fundamentally altering our understanding of all that exists. This theory originated from observations made in the early 20th century, and has since been supported by multiple astronomical evidences.
The idea that the universe is expanding was first proposed by a Belgian priest and astronomer Georges Lemaitre in 1927, who suggested that the universe began from a ‘primeval atom’ and has been expanding ever since. This hypothesis was corroborated by Edwin Hubble’s observations, in 1929.
Hubble discovered that galaxies are moving away from us in all directions, and formulated the Hubble’s Law, according to which, the velocity at which a galaxy is receding is directly proportional to its distance from us. The expansion of the universe is described by the metric expansion of space, which is governed by the equations of General Relativity formulated by Albert Einstein.
Despite multiple efforts, the exact value of the Hubble constant remains a topic of debate due to differing results.
Dark Matter
This gave birth to many other theories, including the existence of dark matter. The existence of dark matter has been extremely crucial for explaining the structure and formation of galaxies, and the large structure of the universe. Without dark matter, the formation of galaxies and large cosmic structures as we observe them today would not be possible.
And yet, despite its critical role, the exact nature of dark matter remains unknown, as it does not interact with electromagnetic forces, making it extremely difficult to be detected directly. Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible to current astronomical instruments. Its presence is inferred from its gravitational effects on visible matter, such as galaxies and star clusters.
The concept was first introduced in the early 20th century when astronomers observed discrepancies in the rotational speeds of galaxies. Fritz Zwicky studied the Coma Cluster and noticed that the visible mass was insufficient to account for the observed gravitational binding of the cluster, and proposed the existence of ‘dark matter’ to explain this missing mass. Later observations by Vera Rubin and others provided further evidence of dark matter by showing that stars in galaxies orbit at much higher speeds than expected if only visible matter were present.
Anti-universe
However, a new theory proposed by Naman Kumar, a PhD student at the Indian Institute of Technology (IIT), Gandhinagar, sheds light on the possibility of an anti-universe that can explain the accelerated expansion of this universe, without the presence of dark matter.
In his paper published in Gravitation and Cosmology, Kumar explains the expansion of the universe, with the existence of an anti-universe, rather than the presence of dark matter. “If we look from a quantum perspective, the most natural way in which the universe can be created is in entangled pairs whose time flow is oppositely related. This suggests the idea of the creation of a universe-anti-universe pair. Assuming the validity of this hypothesis, in this paper, we show that the universe expands in an accelerated manner,” Kumar writes in his study.
The anti-universe is a captivating concept that extends the understanding of symmetry, anti-matter, and the fundamental nature of the cosmos. While the idea remains largely theoretical, it stimulates ongoing research and discussion in theoretical physics and cosmology. The concept of an anti-universe arises from theoretical physics and cosmology and ties the broader understanding of antimatter and the symmetries governing the universe. It also provides new insights into the fundamental structure of reality and the nature of existence, improving our understanding of our universe.
The idea of an anti-universe emerges from the considerations of its theoretical origin, Charge, Parity, Time (CPT) symmetry, and implications and speculations about its fundamental nature. The notion of an anti-universe is grounded in the idea that our universe might have a counterpart, where all particles are replaced by their antiparticles, and time runs in reverse. This concept can be seen as an extension of the CPT symmetry, which is a fundamental symmetry in particle physics.
This symmetry suggests that the laws of physics should remain invariant if you simultaneously reverse the charge (C), spatial coordinates (P), and the direction of time (T). Applying this concept to the universe could imply the existence of a mirror universe composed of antimatter, with time running in the reverse. This hypothetical anti-universe would then be a ‘mirror image’ of our universe, obeying the same physical laws, only that all particles will be replaced with antiparticles.
If indeed an anti-universe does exist, it would be a fascinating counterpart to this universe, and the implications of such a universe would be profound. The anti-universe would have a similar large-scale structure, but composed of antimatter. The fundamental interactions and laws would remain the same, though all particles and antiparticles would be swapped. Detecting such a universe would be extremely challenging. The interactions between our universe and an anti-universe would be limited, but they might become apparent in certain cosmic phenomena or through high-energy experiments.
Kumar argues that from a quantum theory perspective, it is natural for the universe to be created in pairs, and takes reference of a recent study on The Big Bang, CPT, and neutrino dark matter to further explain anti-Universe. A neutrino is an elementary particle that interacts via weak interaction and gravity. “We investigate the idea that the universe before the Big Bang is the CPT reflection of the universe after the bang, both classically and quantum mechanically, so that the universe does not spontaneously violate the CPT.
We show how CPT symmetry selects a preferred vacuum state for quantum fields on a CPT-invariant cosmological background spacetime. The universe before the bang and the universe after the bang may be viewed as a universe/anti-universe pair, emerging directly into the hot, radiation-dominated era we observe in our past. This leads to a remarkably economical explanation of the cosmological dark matter,” reads the study.
Kumar also used concepts like Quantum Theory, Relative Entropy, and General Relativity, to the null energy condition, which suggests that the universe naturally expands in an accelerated manner. “Relative entropy, which requires two states, in this case, corresponds to the universe and its partner anti-universe.
Accelerated expansion seems inevitable in a universe created in pairs that respect the null energy condition,” Kumar states, concluding that using existing theories, the concept of an anti-universe offers an explanation to the cosmic expansion, without the need for elusive dark energy.