Det kan strekke tankene dine til å tenke på hva som egentlig er der ute.
Rett over deg er himmelen – eller som forskerne vil kalle det, atmosfæren. Den strekker seg ca 20 miles (32 kilometer) over jorden. Flytende rundt atmosfæren er en blanding av molekyler – små luftbiter så små at du tar inn milliarder av dem hver gang du puster.
Over atmosfæren er plass. Det kalles det fordi det har langt færre molekyler, med mye tomt mellomrom.
Har du noen gang lurt på hvordan det ville være å reise til verdensrommet – og så fortsette? Hva ville du finne? Forskere liker meg er i stand til å forklare mye av det du vil se. Men det er noen ting vi ikke vet ennå, som om verdensrommet bare fortsetter for alltid.
Planeter, stjerner og galakser
I begynnelsen av reisen gjennom verdensrommet vil du kanskje kjenne igjen noen av severdighetene. De Jorden er en del av en gruppe planeter som alle går i bane rundt solen – med noen kretsende asteroider og kometer blandet inn også.
Et kjent nabolag.
Du vet kanskje at solen faktisk bare er en gjennomsnittlig stjerne, og ser større og lysere ut enn de andre stjernene bare fordi det er nærmere. For å komme til den neste nærmeste stjernen, måtte du reise gjennom billioner av mil med plass. Hvis du kunne sykle på den raskeste romsonden[{” attribute=””>NASA has ever made, it would still take you thousands of years to get there.
If stars are like houses, then galaxies are like cities full of houses. Scientists estimate there are 100 billion stars in Earth’s galaxy. If you could zoom out, way beyond Earth’s galaxy, those 100 billion stars would blend together – the way lights of city buildings do when viewed from an airplane.
Recently astronomers have learned that many or even most stars have their own orbiting planets. Some are even like Earth, so it’s possible they might be home to other beings also wondering what’s out there.
This packed image taken with the Hubble Space Telescope showcases the galaxy cluster ACO S 295, as well as a jostling crowd of background galaxies and foreground stars. Credit: ESA/Hubble & NASA, F. Pacaud, D. Coe
You would have to travel through millions of trillions more miles of space just to reach another galaxy. Most of that space is almost completely empty, with only some stray molecules and tiny mysterious invisible particles scientists call “dark matter.”
Using big telescopes, astronomers see millions of galaxies out there – and they just keep going, in every direction.
If you could watch for long enough, over millions of years, it would look like new space is gradually being added between all the galaxies. You can visualize this by imagining tiny dots on a deflated balloon and then thinking about blowing it up. The dots would keep moving farther apart, just like the galaxies are.
Is there an end?
If you could keep going out, as far as you wanted, would you just keep passing by galaxies forever? Are there an infinite number of galaxies in every direction? Or does the whole thing eventually end? And if it does end, what does it end with?
These are questions scientists don’t have definite answers to yet. Many think it’s likely you would just keep passing galaxies in every direction, forever. In that case, the universe would be infinite, with no end.
Some scientists think it’s possible the universe might eventually wrap back around on itself – so if you could just keep going out, you would someday come back around to where you started, from the other direction.
One way to think about this is to picture a globe, and imagine that you are a creature that can move only on the surface. If you start walking any direction, east for example, and just keep going, eventually you would come back to where you began. If this were the case for the universe, it would mean it is not infinitely big – although it would still be bigger than you can imagine.
In either case, you could never get to the end of the universe or space. Scientists now consider it unlikely the universe has an end – a region where the galaxies stop or where there would be a barrier of some kind marking the end of space.
But nobody knows for sure. How to answer this question will need to be figured out by a future scientist.
Written by Jack Singal, Associate Professor of Physics, University of Richmond.
This article was first published in The Conversation.