Immediately after the Big Bang, the Universe was denser than any object known to exist today. Seemingly, such gravity should slow down time. But it’s impossible to verify this—and here’s why.
Neutron stars as a clue
We know that gravity really affects the passage of time. A neutron star contains twice the mass of the Sun packed into an object the size of a small city. It is so massive that it warps the surrounding spacetime, causing time to pass 1.9 times slower near it than on Earth.
But this slowing down is measured relative to an external clock—one located where gravity is weak and spacetime is not curved.
Proper time and the relativity of measurement
In physics, there is the concept of proper time: each object perceives only the duration of events that occur along its path through the Universe.
If you were to travel to the nearest star at a speed close to the speed of light, only a few seconds would pass on board, while 4.3 years would elapse on Earth. Neither of these clocks is wrong—they simply measure different time intervals for different trajectories.
Immediately after the Big Bang, the entire universe consisted of dense plasma, and every particle was moving at a speed close to that of light. Each particle measured its own time along its own tangled trajectory within this chaos.
There was no “external” place—some distant, tranquil place with an undisturbed space-time continuum—where a standard clock could be placed for comparison.
Difference without a reference point
Next to a neutron star, two clocks located at different points in the gravitational field also run at different rates, and this difference can be measured.
In the first moments after the Big Bang, such a differential effect existed, but the gravitational field was changing so rapidly that it would have been impossible—even in theory—to compare the proper times of individual particles. The absence of an external reference frame makes such a comparison impossible.
Here on Earth, the Big Bang occurred 13.8 billion years ago. For a hypothetical particle, only 10⁻¹⁵ seconds of its own time had passed immediately after the Big Bang. Both figures are correct—they’re just relative to their own reference frames.
According to astronomy.com
