how I know the universe is old

[mellowtigger]

There's a time delay in communications across the globe. When exchanging signals with satellites orbiting overhead, there's always a delay of about 1/4 second for a round trip communication. That's how I know the universe is old, because it takes that much time for light to travel such a teeny, insignificant distance. Consider how much time it takes to traverse the even greater distances around us.

I follow this account that occasionally tweets out the distance from Earth of the Voyager 1 and 2 spacecraft.  The farthest we've sent our instruments is still less than 1 day of travel time for a ray of light.  It takes that long for any signal to travel the distance one-way.

"I am currently 18 hrs 00 min 56 secs of light-travel time from Earth (2022:084:000000:2L)"
- twitter, @NSFVoyager2, 2022 March 24

Using the simple triangle geometry of parallax (the way an object seems to move against the background as you move), we can measure distances to stars about 3,000 light years away.  That's how old the light is before it reaches our eyes when we look up at the sky.  Even farther distances require even older light.  Earth is about 26,000 light years away from the center of our own galaxy, and that's still a tiny fraction of the size of the whole universe.

The light we see in the sky is ancient.  So that's how I know the universe is incredibly old, because there's a lag of about 1/4-second when we try to hold a long distance communication with someone else around the globe.  The universe has a maximum speed limit, which means the universe has a minimum age boundary too.

It's an amazing place.

Comments

[mellowtigger]

I'm not the only one who thinks this way.

"The observable universe is more than 90 billion light-years across. So far, no human has ventured farther than 1.3 light-seconds from Earth."
–Brian Greene (physicist)
- twitter, stevestuwill, 2022 Sep 09