The universe isn't just growing; it is being pushed apart
In short: For centuries, we believed gravity was a universal glue, pulling every object toward every other object. But modern astronomy reveals a startling truth: something is actively pushing space apart. This mysterious repulsive force makes up the vast majority of our cosmos and dictates its ultimate fate.
To understand this 'anti-gravity,' we must look at how our understanding of gravity evolved. Isaac Newton first defined it as an attractive force proportional to mass. However, in 1915 and 1925, Albert Einstein revolutionized the field with General Relativity. He proposed that space and time are not independent but form a single 4-dimensional continuum called spacetime. In this model, gravity is not just a pull; it is the geometry of spacetime warping under the influence of mass and energy.
If mass curves spacetime to create attraction, why does the universe expand at an accelerating rate? Astronomers expected the expansion to slow down over time due to the collective gravitational pull of matter. Instead, observations of distant supernovae in the late 1990s revealed that the expansion is speeding up. This suggests a repulsive force known as dark energy.
Unlike normal matter, which accounts for only about 5% of the universe's energy, dark energy makes up roughly 68%. Dark matter accounts for the remaining 27%. The mechanism behind this repulsion lies in pressure. According to the Friedmann equation—a way of rewriting Einstein’s equations—accelerated expansion requires either negative energy or negative pressure. While normal matter and radiation exert positive pressure and attract one another, dark energy possesses unusual negative pressure. In a scenario known as the 'cosmological constant,' this energy density remains unchanged as space grows. Consequently, a constant energy density implies that expanding space generates additional energy, which triggers an ever-faster growth rate potentially responsible for the universe's swift development within the initial millisecond post-Big Bang.
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- Summary by Intellect · source: Anti-Gravity, the Force that's Tearing Space Apart!
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