The Great Conundrum: Would Everything Eventually Touch If the Universe is Infinite and Expanding?
One of the most intriguing mysteries of cosmology is this: if the universe is infinite and expanding forever, why wouldn't everything eventually come into contact with each other? The apparent contradiction between the vastness and the continuous expansion of space has puzzled cosmologists for decades. Let's delve into the complexities and unravel the paradox.
Understanding the Basics: Galaxies and Dark Energy
Galaxies are the fundamental building blocks of the universe. With enough internal gravity, they can remain stable and cohesive for an eternity. Importantly, the expansion of space does not disrupt galaxies. Dark energy, the force driving the expansion, has no apparent effect on the internal composition of a galaxy, such as its stars, gas, black holes, or other celestial bodies.
The Expanding Universe: An Eternal Phenomenon
It is widely accepted that the universe continues to expand, and this expansion will persist indefinitely. Given this reality, the universe will eventually consist of widely dispersed galaxies. However, some galaxies will eventually merge, forming larger structures. This expanding nature of the universe is a key concept in modern cosmology.
The expansion of the universe is not a simple stretching of matter, but a stretching of the space itself. Beyond tens of millions of light-years, where gravity dominates, the separation between objects like galaxies and isolated stars is increasing at the Hubble rate, which is approximately 68 kilometers per second per megaparsec.
Visualizing the Expansion
A useful analogy is to envision the universe as a balloon with galaxies as raisins. As the balloon inflates, the raisins separate, but they do not move relative to each other. The rate of separation is proportional to their distance. Therefore, objects like galaxies farther apart expand faster, and those more than 14 billion light-years apart are expanding faster than the speed of light.
This concept can also be understood through the idea of the Hubble sphere, which is the distance beyond which the recession velocity of a galaxy exceeds the speed of light, due to the expansion of the universe. This is analogous to the "surface" of the balloon where the raisins are moving away from each other, but they are not moving themselves.
Addressing the Concept of Proximity
The term "right next to each other" is relative. In the context of an infinite universe, if it started out finite, it would require infinite speed to expand infinitely. For the universe to be infinite, it must start out infinite, and everything within it, from quantum fields to virtual particles, must also be infinite. Thus, for practical purposes, the idea of everything being "next to each other" is a misinterpretation.
The expansion of the universe means that objects are getting progressively further apart, not closer. The rate of this expansion has been measured at about 70 kilometers per second per megaparsec for objects beyond the gravitational influence of other objects. An Mpc (megaparsec) is approximately 3.3 million light-years.
Therefore, the further apart two objects are, the faster they expand away from each other, making the concept of everything eventually touching a misrepresentation of the reality of the expanding universe.
Understanding the universe's infinite and expanding nature helps us appreciate the vastness and complexity of our cosmos. The expansion of space is not a force that brings things together but a force that separates them further apart over time.
Conclusion
If the universe is infinite and expanding, it doesn't mean that everything will eventually touch each other. On the contrary, it means that everything is getting further apart. This expanding nature is a fundamental aspect of the universe, driven by mechanisms such as dark energy and the curvature of space-time. The mysteries of the cosmos continue to challenge and captivate the minds of scientists and enthusiasts alike, inviting us to explore the boundaries of our understanding.