Sunday, October 10, 2010

Quantum Mechanics - On Time Travel & Black Holes

Quantum physics - one of my favorite subjects to read about. And luckily for me, the science world seems to be teeming with news and reports on the latest theories in this area. I don't really understand much about it, but I think that is why I like it so much. Kinda like Fantasy, quantum theory is like magic. You don't know how people in fantasy books can turn eachother into donkeys, but you accept the idea and love that it is possible (in that fictional universe). In a way this is how I feel about Quantum Physics. I don't really understand the concepts of entanglement, multiverses or the fact that time might not exist, but I accept the idea and love that it might be true. Quarks and uncertainty principles are the reality equivalent of unicorns and dragons.

I recently read a really good book on the subject - Stephen Hawkings & Leonard Mlodinows "A briefer history of time". The two authors have set out to explain the universe, time and quantum physics for simpletons like me, and they're doing an awesome job. They start out really simple, with the very basics. A history lesson takes me briefly through the evolution of the view on how the universe has worked. All the way from the earth being a disc on the back of a bunch of turtles to the view science has today (I say science since not all agree with this view). They explain the ideas behind gravity and Einsteins relativity principle, and also some of the fallacies and traps that scientists easily fall into - the need to adapt a theory so that it works with how one already thinks the universe works. Even Einstein did this mistake, but he admitted to it afterwards.

I won't and I can't go through the entire book, but I will highlight some of my mind-boggling favorites. If you find them interesting or just don't understand what the heck I'm talking about (don't worry, neither do I), I really recommend checking it, and other similar works by Stephen Hawking & friends out!

Time is not absolute
This is probably no news to most people out there by now. Einstein showed that even something that seems as constant as time, is quite relative. Time is in the eye of the beholder so to speak. In our day to day doings we won't notice this much, the difference in time between us are so small that we don't notice them. Or rather they are so common that we don't notice them. Just like we don't notice the weight of all the air pressing down on us every day. It is a setting we're in every second of every day and are adapted to work in, so to us everything seems quite normal, and as mentioned, quite constant.

There are differences however, and thinking about them is fun even if they don't actually affect us on a bigger scale. For instance, time is affected by gravity. The closer to a gravity source something is, the slower time goes. That means that someone standing on a chair will move faster in time than someone standing on the ground beneath him! The difference in time is some 0,001 seconds (or something like it) in 80 years, but it is measurable. It would even be noticeable if we increased the distance. Wonder how slow time would go inside a black hole then?

In fact, if an astronaut was standing on a star about to become a black hole, and sending out messages to a space ship in the vicinity, the orbiting space ship would notice that the last message, the milli-second before the star turns into a black hole, would never come. To the astronaut time would flow as usual. But since the gravity in the black hole is so high, time is slowed so much that everyone outside of its force will think the final message never arrived. To the space ship, the time period between the second before collapse, and the second of collapse would be infinitely long. To the astronaut on the surface everything would be like normal.

Unfortunately, since the gravitational force of a black hole is so huge, the difference in force between the astronauts head and his feet would tear him apart. These differences are so small on earth that we don't notice them (but as mentioned they're measurable for example through the difference in passed time).

On a side note, we all know that time can be quite relative from playing WoW ;) I was sure I just re-imbued my weapons with wf, just like 3 minutes ago! And now I have to reapply it? It can't already have passed 30 min... can it?

Are our actions predestined? Do we have free will? Can we predict the future?
One interesting thing about science is the notion that if we could measure everything and understood the relationship between everything, we would also be able to predict the future. All our actions would after all be the cause and effect of other causes and effects. That means that whether I decide to write this text is all determined no matter if I "want to" or not. The action potentials in my brain that make me want to do this have been affected by outside sources and are in turn affecting outside sources. To make it more clear - picture a pool table. You're about to do the first shot, knocking all the billiard balls around. Whether one of the balls will go into a hole isn't really affected on any will of the balls itself, it is entirely affected on how you do that shot. So what if your shot in turn is affected by situations that are out of your control? In essence, we're all just billiard balls rolling around in the universe without any say about it.

It does seem probable, but quantum mechanics changes this. And here comes an explanation I don't fully understand. when it comes to quantum mechanics there is always a chance element. Even if some outcomes of an action are considerably higher than others, there is always a chance something completely else will happen. Say you throw a ball against a pole. If you know everything about the throw, the strength of the throw, the pull of gravity, the weight of the ball and etc, you can calculate the chances that the ball will hit the pole. And those calculations will be very exact. But not 100% exact. According to quantum theory there is always a chance that you'll miss the pole even with a perfect throw! Now the chance is so small that even if you threw that ball until the end of time you probably wouldn't miss. But the chance is there and it puts a small element of randomness into everything we do. It doesn't answer the question to whether we have free will or not. But it would at least make the future not entirely predictable, not even if we had all the facts. Einstein did not like this idea at all and simply said "God does not play dice". Or - there is no such thing as pure randomness. Well, who knows?

We'll probably never ever be able to measure all the factors of all events that ever happen anyway, so even if predicting the future might be theoretically possible, it probably never will be in practicality. We might become better and better at guessing, but never 100% sure.

What lies beyond space?
I bet everyone who's ever tried to understand the universe has asked themselves "but what lies beyond the boundaries of space then?". Or "what was before our universe?". There is a possibility that space not only lacks an end, but also a beginning. Try to wrap your mind around this baby. If space is curved around itself, it would go on eternally in all directions and if you travelled in a straight line you'd eventually end up where you started. Kinda like a Möbius Strip but also in time. Or like the surface of the Earth, it continues endlessly without any beginning or end somewhere.

This is a really tricky one! We see time as a line of events with something beginning and ending. That is how we see things on earth. A human is born, lives and dies. On a molecular level a human doesn't really "begin" with birth or "end" with death of course. The elements of that human existed before they were born and will continue to exist after they've died, so the notion of "beginnings" and "endings" is really an illusion. But it is a very good illusion. So good in fact that we're having an extremely tough time trying to understand something that might not begin or end anywhere, even if that is in fact the normal state of things. (Just like there really isn't any up or down in space!).

Hawkings proposes that the universe is without boundaries, both in space and in time. It curves around itself and as thus it just simply exists. If we think really, really hard about it it seems more logical for something to simply exist than having to go through the troublesome work of beginning and ending somewhere. The beginnings and endings create more questions than they answer. As such, the universe isn't created. It just is.

Can we travel in time?
I've never believed in time travel. I've never seen time as linear, but more as one moment replacing the next. I've always seen time as the change of matter, rather than it's own outside force. The idea of time travel is based on the idea that time is absolute (see above) which it isn't. The prevailing idea of time travel is that travelling in time is like swimming up or down a stream. But if we look at time the way relativity describes it and think about some of the things mentioned above, a sort of time travel would be possible.

Someone travelling at the speed of light would move slower in time than someone who doesn't. Or going back to the poor astronaut on the surface of the collapsing star, he was moving infinitely slower in time than the people in the space ship above. If this astronaut could somehow get away from the collapsing star some seconds afterwards (what would feel like seconds to him) he would have moved so slow in time (compared to the rest of the universe) that to him it would feel like travelling far into the future. The difference is of course that he has actually travelled the same distance, but he just hasn't aged at all (i.e his matter hasn't changed as much as the surrounding universes), and to him it felt like it only took a matter of seconds. He hasn't actually jumped from one time to the next. This kind of time travel would be like a sped-up cryo-sleep.
So can we travel back again from that?

A famous mathematician named Kurt Gödel proposed in 1949 that space was rotating. Without being too technical about it, it would mean that it would be possible to leave earth at a time and return before you left. Unfortunately no one has been able to measure whether the universe is really rotating, so this kind of time-travel doesn't seem very likely.

Another way to travel back in time would be if we could travel faster than the speed of light. That is because under these conditions the order of events would be scrambled. That means one person could experience travelling back in time - because he's experiencing things reversed as compared to everyone else, while to everyone else the order of events are as "normal". No I don't understand it either. Since travelling faster than light takes an infinite amount of energy (or so says the relativity principle anyway), it doesn't seem like it's anything we have to worry about just yet.

Phew, I was just going to pick some highlights of this book and I end up with this huge rant. As you can see it is a subject that really interests me ^^ Yet again, I strongly recommend checking out any book on this subject, and Stephen Hawking (together with Leonard Mlodinow) has made a tremendous job making this extremely difficult subject interesting and somewhat understandable for the layman!
Thanks to wikipedia for the pictures!


  1. I recommend "Physics of the Impossible" by Michio Kaku, he discusses all those things and it´s really fun. According to him, ony two of the popular SF ideas would be completely impossible because they violate fundamental physical laws. And those are perpetual motion machines and precognition. So, everything else just might be possible one day!

  2. If you are interested of quantum mechanics, gravity and black holes, i can recomend the following books for you. Some of it is technical, but i am convinced that you can understand it ;-)If not, feel free to ask.

    Svenska Fysikersamfundets årsbok- Kosmos 1991.
    Den moderna fysikens grunder/Krister Renard.
    Space, time and gravity/Robert M.Wald
    Gravitys fatal attraction/Mitchell Begelman+Martin Rees.

    Best regards Stefan

  3. Thanks for the tips! I'll definitely check them out :)

  4. I recommend "Quantum" by manjit kumar.