Time travel using black holes
Time travel, it exists. Awesome! Did you know that time travel already exists in our universe? If you are from an advanced enough civilization you could already use it. All you need is a black hole and a spaceship that can move at near light speed.
Image below is an artistic conception of this idea.
One of the coolest and most interesting objects in space is black holes. Points in space where gravity is so strong, we don't know what goes on beyond the event horizon (behind the black veil of the event horizon). These objects have incredible levels of influence and literally bend space-time around them. They do this to such an extent, they can have some incredible effects on any objects around them. For example if you get too close, nothing and no-one can get away from them. Even light.
Before we do the hypothetical jump to bear the black hole, let's step back for a moment. Around any black hole is an imaginary boundary called the event horizon. This boundary is critical, because once you cross it (we believe) you can never come back to our universe. It is the region around any black hole when light can no longer escape the black hole, but will spiral into it, being trapped and in a sense, consumed by the black hole. This is key, because to time travel we need to get near, but not go over the event horizon.
In order to time travel effectively in our universe and jump to the future. You will need to go near and even orbit a black hole outside of the event horizon. Since the gravity is so strong in this region of space-time, time will slow for you relative to the rest of the universe. You won't feel it, you won't sense it, but time outside the black hole's influence will move faster and time near the black hole slows down (essentially). This means if your spaceship could move fast enough and withstand the forces long enough you might be able to jump into the future like in the movie Interstellar.
Now while your regular sized black hole will shred any object that comes near it due to what are known as tidal forces where the gravity is chaotic and moves in small energetic ways that could mess up a spaceship. Supermassive black holes like the one at the center of our Galaxy (called Sagittarius a) do not have strong tidal forces and might allow the spaceship to make it around without ripping it apart with gravitational forces. Remember: the smaller the black hole, the greater the tides (and risk of death).
Image below is a supermassive black hole with an accretion disk of material falling into it.
So what about the future? Well that just isn't sure, there are a lot of theories and some crazy ideas, but at the moment it just doesn't look like a likely possibility. While time travel to the future is possible and even plausible today according to our physics, time travel to the past is still relatively unknown and remains to be a mystery for our future and great science-fiction stories for now.
If you are a teacher or parent and interested in supporting your young person with learning about astronomy. Perhaps my crash course video companions would help - link here.
Thanks for reading.
Cheers and stay curious
Oliver - The Teaching Astrophysicist
(Note: This blog post was NOT generated by AI and is conceived, typed and uploaded by a real person.)