When we look into the night sky, we see the universe as it once was. We know that in the past, the universe was once warmer and denser than it is now. When we look deep enough into the sky, we see the microwave remnant of the big bang known as the cosmic microwave background. That marks the limit of what we can see. It marks the extent of the observable universe from our vantage point.
Click here for original story, Understanding the early universe depends on estimating the lifespan of neutrons
Source: Phys.org