Dark Matter and Energy

The Expanding Universe and the Mystery of Dark Matter 

In 1929, astronomer Edwin Hubble made a groundbreaking discovery while studying distant galaxies. He observed that almost every galaxy was moving away from Earth, indicating that the universe was expanding. This phenomenon can be understood using a concept similar to the Doppler effect, which we commonly experience with sound. 

For example, when an ambulance approaches, its siren sounds higher in pitch, and as it moves away, the pitch lowers. This occurs because sound waves are compressed when moving toward us and stretched when moving away. A similar effect applies to light waves: 

• Redshift occurs when an object moves away from us, stretching the light waves and shifting them toward the red end of the spectrum. 

• Blueshift happens when an object moves closer, compressing the light waves and shifting them toward the blue end of the spectrum. 

The Hubble Space Telescope, which orbits Earth, uses this principle to analyze the light from distant objects. By measuring redshift, astronomers have determined not only that the universe is expanding, but also that our neighboring galaxy, Andromeda, is on a collision course with the Milky Way. This grand merger is expected to take place in approximately four billion years. 

The Mystery of Dark Matter and Dark Energy 

In the 1930s, Dutch astronomer Jan Oort made another startling discovery. He studied the velocity of stars in the Milky Way and found that they were moving faster than expected based on the visible matter present. According to Newton’s laws, an object moving at high speeds should eventually break free from gravitational pull. However, the stars remained in orbit, suggesting that an unknown force was acting upon them. 

Oort estimated the total mass of the Milky Way and found that visible matter alone was insufficient to explain the galaxy's rotation. This led him to propose the existence of an invisible, mysterious substance—which we now call dark matter. Later studies revealed that dark energy—a repulsive force—was responsible for accelerating the universe’s expansion. 

Current estimates suggest that the universe consists of: 

• 5% normal matter (everything we can see: planets, stars, galaxies) 

• 27% dark matter (which exerts gravitational pull but does not emit light) 

• 68% dark energy (which counteracts gravity and pushes the universe apart) 

The Fate of the Universe 

The question remains: Will the universe expand forever, or will it eventually collapse? 

Some ancient Hindu texts propose an interesting perspective. According to Hindu cosmology, the universe follows a cyclic pattern, where it exists for 4.32 billion years during the day of Brahma, then ceases to exist for another 4.32 billion years during Brahma’s night. This theory loosely resembles the idea of a Big Crunch—a scenario where the universe eventually stops expanding, contracts due to gravity, and collapses back into a singularity, possibly leading to the birth of a new universe. 

However, given that the universe is currently expanding at an accelerating rate, the Big Crunch theory is unlikely—at least based on our current understanding of physics. Instead, if dark energy continues to dominate, the universe may keep expanding indefinitely, growing colder and emptier over time. 

Final Thoughts 

From Edwin Hubble’s discovery of an expanding universe to Jan Oort’s revelation of unseen forces shaping galaxies, our understanding of the cosmos continues to evolve. The universe is vast, mysterious, and full of unanswered questions. While we may never fully grasp its complexities, each discovery brings us one step closer to understanding our place in this grand cosmic journey.