This seems like a very simple question. But as this video from vsauce shows, it’s anything but. This goes into things way past my middle school classroom, including general relativity, spacetime, and geodesics. Things are simplified in middle school, and it’s still a difficult thing for kids to get. More below the video.
In middle school we’re more interested in the Newtonian view rather than the spacetime view. For us, down is towards the center of the Earth. It’s the same for people on the other side of the Earth (say in Australia (I’m in New Jersey, USA)). For them, down is still towards the center of the Earth, but that’s in a different direction. My down and their down point in close to opposite directions. That’s because the concept of “down” is a local direction, not a universal one. My down is different from the down of my friend who lives in New Zeeland. This can be a difficult thing for 13 year olds to understand. It helps to show it on a globe, with little stick figures drawn on a folded up sticky notes.
So stars are born, they live, and they die. Large stars die in a supernova. And that’s it.
Except that it isn’t. Scientists have found a star that has had multiple supernovas. One in 1954, the other in 1993. This is impossible given our current understanding of how stars work. Which means that we need to change our understanding. Our current theories are wrong and need to be changed. This is the exciting part of science, when our understanding has to change to fit the facts.
Have you ever had a thought that just keeps on coming up even though you wish it would just stop? This is very common with people who have PTSD, depression, anxiety, and more.
Research done at the University of Cambridge has found that one particular neurotransmitter, GABA, may be the key to help avoid these thoughts in the future. Research using FMRI and magnetic resonance spectroscopy have found that the presence of GABA can inhibit the activity of connected memory neurons. It may be that increasing the amount of GABA could help reduce the amount of persistent unwanted thoughts.