Byline: Ahmed, Science Correspondent
Intriguing questions about the cosmos have always captivated humanity’s imagination. One such enigma: How fast is the universe expanding? As experts grapple with this cosmic riddle, the first step is understanding the vastness of our universe. According to their estimations, the farthest observable corners of the universe are a staggering 46 billion light-years away, with a mind-boggling diameter of 540 sextillion miles (that’s 54 followed by 22 zeros). Yet, these figures are merely approximations.
Our universe, born approximately 13.8 billion years ago in the cataclysmic event known as the Big Bang, has been expanding ever since. To quantify this expansion, astronomers have turned to a critical value known as the “Hubble constant.” Princeton University’s esteemed astronomer, Rachel Beaton, emphasizes the need for rigorous testing to obtain an accurate measurement.
The journey to determine the Hubble constant began in 1929 when astronomer Edwin Hubble made the first measurement, setting it at 500 km/s per megasecond. This constant represents the delicate equilibrium between two opposing forces: gravity, which pulls celestial bodies together, and the centripetal force, which seeks to propel them apart. These forces have shaped our universe from its earliest moments.
Over the past century, Hubble’s original estimate has undergone numerous revisions. Recent calculations place the Hubble constant between 67 and 74 kilometers per second. The variance arises from two different measurement techniques.
One approach examines the velocities of nearby galaxies as they recede from us. The other leverages the cosmic microwave background (CMB), the universe’s first light, emitted during the Big Bang. This ancient light, still observable today, permeates as radio waves, offering a glimpse into our universe’s primordial state. It reveals subtle temperature differences stemming from the early cosmic clash between gravity and radiation’s centrifugal force.
These insights enable astronomers to extrapolate the universe’s initial expansion rate following the Big Bang, an invaluable tool in modern cosmology’s Standard Model. However, a perplexing divergence emerges when comparing these methods. Measurements from nearby galaxies yield a slower Hubble constant, around 67.4 km/s, while CMB anomalies, discovered by the European Space Agency’s Planck satellite, suggest a faster rate, almost 9% faster.
To bridge this cosmic divide, scientists are harnessing the power of Cepheid variables, stars that subtly brighten and dim over weeks, offering precise brightness measurements and enabling distance calculations. If the universe indeed expands more rapidly than estimated, it implies an age younger than the current 13.8 billion years.
Friedman and his colleagues employed Cepheid variables in neighboring galaxies to derive a Hubble constant of 72 kilometers per second per megaparsec (MPC) in 2001. Other astronomers, using the same technique, reached 74 km/s per MPC with the Hubble Space Telescope in 2019. Additional measurements from quasars, extraordinarily distant objects emitting copious radio waves, yielded a value of 73 km/s per MPC.
These measurements challenge the Standard Model’s predictions, suggesting the universe expands even faster. The mysteries abound: Is the model flawed? Are the proportions of subatomic particles, normal matter, dark energy, and radiation askew? Or does our universe’s corner differ fundamentally from the rest?
Fortunately, scientific advancements are on the horizon. The European Space Agency’s space observatory, operational since 2013, measures nearly a billion stars with remarkable accuracy. Parallax measurements, gauging the movement of stars relative to our solar system, promise precision in determining stellar velocities.
Moreover, the forthcoming James Webb Space Telescope, launching soon, will utilize infrared wavelengths to refine measurements, unaffected by interstellar particles. Dark energy’s possible evolution over time presents another avenue for exploration, potentially altering our understanding of the universe’s expansion.
In conclusion, as we gaze upon the ever-expanding cosmos, questions remain unanswered, awaiting the breakthroughs of tomorrow. Our quest to comprehend the universe’s secrets continues, a journey ripe with opportunities for discovery and revelation.