The universe's expansion can cause distant galaxies to recede faster than the speed of light, a phenomenon consistent with Albert Einstein's theory of relativity. This expansion does not mean objects are moving through space faster than light. Instead, the space between galaxies is stretching.
Measuring cosmic distances is complex due to this expansion. Light from distant galaxies travels for billions of years. During this time, the universe continues to expand. This means that a galaxy's current location is much farther away than its position when the light we observe was emitted.
Astronomers use cosmological models, such as the Lambda-CDM model, to account for this expansion. These models help estimate the present distance of galaxies. The observable universe, currently about 45 billion light-years in radius, is much larger than its age of 13.77 billion years suggests.
Special relativity limits how fast objects can move through local space. However, it does not restrict the rate at which space itself can expand. Galaxies recede faster as their distance increases, a concept Edwin Hubble observed through redshift measurements. The Hubble distance marks the point where galaxies begin receding faster than light.
We can still observe galaxies beyond the Hubble distance because their light began its journey when they were closer. However, there is a cosmological event horizon, currently about 17 billion light-years away. Light emitted from beyond this boundary now will never reach us due to the accelerating expansion of space.
Dark energy drives this accelerating expansion. In approximately 100 billion years, all galaxies beyond our Local Group will disappear from view. Future observers will perceive a much smaller and emptier universe.
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