Cosmological Horizon

Monday morning.  I am leaving my flat. I am a little bit late and will have to attend an important meeting at work. I am trying to get the bus. Just as I reach the bus, the bus driver makes eye contact with me and closes the door right before my face. Damn it! I get on the bus right after that. Of course, we are stuck in traffic. I am not in time for the meeting and get in trouble with my superior. I somehow make it through the day but get into a fight with my girlfriend over some small, unimportant thing.

On days like these, it can really feel as if the whole world is conspiring against you. Time is too little, the world just unfair and you feel like you have a streak of really bad luck. When objectively small and important things start to drag me down, I try to think of the things that are really big. Far away galaxies, worlds and infinite distances to travel, to explore, to look forward to once we are technologically advanced enough as a species.

Artistic interpretation of a starfilled night sky at the horizon.
Artistic horizon. Credit: Luminas_Art / Pixabay.

But it turns out we might not have as much to explore as most of us think. Space is expanding and galaxies are moving away from us. That means, with increasing amount of space between us and distant galaxies, the rate at which more and more distant worlds recede from us grows exponentially. Ultimately this means that there is a certain distance, at which galaxies move away from us with a speed greater than c (the speed of light), which makes them unreachable for us with almost all means of transportation that we can think of at the moment. This distance is called the “cosmological horizon” – everything beyond that distance can never be reached by us with conventional means of transportation. In fact, at this moment, already 94% of the observable universe is beyond that horizon. So, we can still detect the light that reaches us from those distant pockets of space for the next billions of years, but we will never able to reach them, as so much space is expanding between our location and the parts of our universe beyond that horizon.

At first sight, it seems like a depressing or sad thought, as so much of the universe is just there before our eyes but we will never be able to reach it. But when you really look at the remaining 6% of the universe we still have 120.000.000.000 (120 billion) galaxies to explore, each with its own 1.000.000.000 (1 billion) stars! Thinking about this always settles me. It reminds me of the fact that everything is changing. Some things will be lost, but there is still so much to do, accomplish and explore. Only by considering this transience you start to understand how precious the current moment is!

So, my dear reader, if you hesitate or are unsure about something: Get up, start moving and take action!

Time is running, but right now there is still some left!

P.S.: For everyone interested – Here is an interesting video form Kurzgesagt on the topic: https://www.youtube.com/watch?v=uzkD5SeuwzM

Tim Erichlandwehr

phD student at DESY who loves to ponder and discuss anything scientific and counterintuitive.

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