ELIF: how is time relative?
In: Physics
Easiest method, listen to a few heavy metal songs (or other high tempo music) until you can comfortably keep the tune in your head and follow along, almost natural and not fast at all you would think.
now, listen to classical music or other low tempo music, it will seem dramatically slow. keep listening until it feels regular speed and comfortable to follow.
Now, listen to the exact same heavy metal/high tempo music, it will be retardedly fast.
Time hasn’t changed, your perception of it has. Time is relative to your perception of it, your brain can speed up that perception if there are too many things coming at you (high tempo) and you only need to take in the important parts (melody of a song) making time appear fast. Likewise, it slows if there are very little things coming at you (low tempo) and your brain has enough time to analyze every detail of seemingly detail-less things. Making time appear slow.
This can also be viewed as how older generations feel like their time is fleeting and just whizzing by. They arent open to learning new things, experiencing the finer details of life because they’ve seen and done a lot of it already, so time appears to move by them at a fast pace.
When you are younger, everything is new, your brain is constantly learning even if you don’t know it is, new school? new people, new smells, new lighting, new everything. Yout brain is on overtime trying to analyze it all, which makes time appear dreadfully slow. Ever wonder why summer vacation as a kid felt like a small eternity but as an adult it just passed by like a missed opportunity?
This is why.
Okay, this is a hard question to answer in a satisfactory way since the idea of time being relative is against all of our intuition. However the conclusion came from some rather intuitive assumptions – those assumptions just lead to some wild conclusions. Let me explain.
Special relativity (the branch of science that explains how time can differ for non accelerating reference frames without strong gravity) was highly motivated by some weird results that physicists got in their study of electricity and magnetism. Today we use 4 equations to describe the laws of electromagnetism. We call these Maxwell’s equations. These equations describe how electric and magnetic fields behave in the presence of charge. If you combine them in a certain way, you get something called a wave equation.
Now a wave equation has certain properties. It showed that electric and magnetic waves can be created, and that they travel at a certain speed that we’ll call C. It turns out that this speed matched closely with light. Thus we concluded that light was an electromagnetic wave. However, and this part is important, one peculiar thing about the equation is a speed popped up without there ever being a reference frame explicitly. That is, the equation said the waves traveled at speed C, but it wasn’t clear who or what was measuring that speed. In other wave equations, it was always obvious from context – such as waves in the surface of water moved relative to the still surface of the water – the median through which the wave propagated. No such median was known to exist for light.
Now scientists resolved this by claiming light traveled through some unseen median called the ether. They tried to look for this ether in experiment but failed. Instead, Einstein came in and claimed something else. He claimed that if you were still, or if you were moving in a car at a constant velocity, the laws of physics would be the same. Now, we intuitively can see this. Throw a ball up in a car, and it will come back down the same way as if you were still. But Einstein extended this idea to light. Measure the speed of a beam of light, then you will get the same answer whether you are in the car or not.
However, that conclusion immediately contradicts are intuition. Say, I’m traveling on a spaceship going half the speed of light and I shine a flashlight in front of me. For me, the light would be going 1C. For someone outside, we would intuitively think they would see the beam of light traveling at 1.5C, since it’s in a spaceship that is travelling at .5C. Einstein says that’s wrong. He says that the beam of light looks like it’s traveling at 1C to both users.
Say for the person in the spaceship it takes one second for the light beam to hit the front. How does that look for someone in the outside? The light moves the same distance in that time, but the front of the spaceship also moves. So to them, the light takes longer to reach the front. IThis is weird to us. Because we insisted that there speed of light is the same for all viewers, something else has to budge. And since velocity is distance over time, the thing that budges is how we measure both distance and time.
It turns out to reconcile the reference frames, things that are moving relative to you appear to slow down. Moving things appear to shrink as well.
This is not an easy concept to grasp, because it is not evident in our day to day lives. Hopefully this gives you motivation to understand why time has to budge.
The speed of light is constant (in a constant medium).
If we were able to be an observer on an object traveling at half the speed of light and we were to turn on a flashlight in the direction we were going, it would appear that the light traveled away from us at the speed of light. We might assume that to a stationary observer the light leaving the flashlight would appear to travel at 1.5 times the speed of light. But this would be impossible because the speed of light is constant and can’t be exceeded.
The thing that has to alter to keep the speed of that light constant for all observers is time. Our time would pass differently than the time of the stationary observer.
When you move fast (and by fast we talk about significant fractions of the speed of light — 100mph isn’t “fast” here), there are 2 things that happen:
– for you, you experience time moving at the same rate you always experience time. The second hand on your watch would still tick once a second.
– for someone else who is standing still watching you, they see your time as going much slower than their time. If they could see your watch, the second hand would be moving much slower.
The faster you go, the slower your time appears to an observer looking at you.
Interestingly, when you look at the person who is standing still, you will see their time as moving much slower too — if you could see their watch, the second hand would also be going slow. This is because, from your perspective, you are completely still and they are moving very fast. (This is relativity)
Time, speed, and relativity are interesting, but very strange, phenomena.
One consequence of this is that anything that travels at the speed of light (a photon, for example) basically experiences no time passing. So a photon that leaves a star 100 light years away would take 100 years to get here, as we would observe that photon. From the photon’s perspective, no time passed at all!
Lets say you are on Earth, but you have a friend that lives on Mars. For some reason, suddenly the sun goes out/disappears. It takes 8 minutes for the light the sun was emitting to stop reaching you. You just happen to have a magic phone that can talk to your friend on Mars instantly. You call him up and tell him the sun has vanished. He is confused and has no idea what you are talking about because he can still see the sun so he hangs up on you. 4 more minutes later, he calls you back on his magic phone and apologizes, the sun has just disappeared for him too!
Four years later, your distant relative that lives on a planet orbiting Proxima Centauri calls you up on his magic phone asking why the hell the sun just disappeared. Of course this is old news to you by now.
For each of the three people in this story, you, your friend on Mars, and your distant relative on Proxima Centauri, they all saw the same event occur at a different time. Time is relative because things do not travel instantly. It takes time for changes in one area of the universe to propagate to others. This is called the speed of causality and just so happens to be the speed light (and other electromagnetic/gravitational waves) travels as well.
The place to start is here: the universe has some kind of underlying set of fundamental rules. We know about 30% of those rules. In the past when I have posted a statement like that I received a huge number of replies saying that’s absurd and we know so much less, or that there is no way to know how much we know, etc. etc. etc. That’s why I like to do it. If we knew 90%+ of the rules we would feel pretty confident about things. If we knew <10% we wouldn’t even be able to make a sensible guess. We do OK. There is a ton we don’t understand, probably we mostly don’t understand, but we have definitely identified a bunch of basic particles, we definitely understand at least a few fundamental forces, and we have enough understanding that often our guesses and deductions about how things should work based on what we have seen prove to be true.
That’s a lot of setup for the actual answer.
The answer is we don’t really know. Time is slippery at the moment. Some people think it doesn’t even really exist. I have a very hard time accepting that proposition. What we do know is that the structure of the universe can be bent by gravity and time bends with both gravity and speed.
Lets take two examples. First. If I built a huge rocketship that could travel at just under the speed of light, I could point it at a distant galaxy a billion light years away, climb in, step on the gas, and I would be able to get to that other galaxy and still be alive. To me it would take a few months. Anyone watching me do it from Earth it would look like I was frozen in time inside the rocketship. The ship would be moving ahead at near the speed of light, but I would be frozen in time.
Second. Lets turn it around, if I could watch the people on Earth running around it would look as though they had been sped up. Is time going slower for me, or faster for them? Its harder to say than you might think.
The point is that time is really relative to the observer.
As far as theoretical physics goes, time doesn’t really exist. It is just how our brains process cause and event. But, our perception of time flowing is also based on where we are and how fast we are moving. If you look at other thing, you are always “stationary.”. So, if you are in a car driving at 60 mph, someone standing on the side of the road is actually moving past you, from your perspective.
This means, for you, time is constant, but that guy outside appears to move much slower since your relative speeds are different. Now, will you see a difference? Absolutely not.
However, experiments have shown that time dialation is real and measurable.
Time is essentially a way of measuring change (or ‘movement’)
If nothing ever changed you’d have no way of knowing that time was passing.
Think of a photon bouncing between two plates. An observer (observer 1) will measure the frequency as a value based on the speed of light. This photon is traveling the same path back and forth (Only movent along a y-axis). Now imagine a second observer (observer 2). One that observes the photon, plates and observer 1 moving as a system perpendicular to the movement of the photon bouncing back and forth. To observer 2 the photon is experiencing movement that lengthens the distance traveled between the two plates (movement in x-axis AND the y-axis). Since a photon can only trave at c, the frequency at which this observer measures the photon will be different AND slower than a photon he measures moving in a simple y-axis pattern within their own reference. Both observers measurements are accurate but different depending on the reference point.
Time is simply a mental construct we project onto motion. It’s an intellectual convenience we use to make sense of reality. Without motion, time would not exist. And without matter, motion cannot exist.
So, for example, historically, people marked the passage of time by the movement of planets. People today use clocks, which are just objects which feature regularly occurring intervals, reliable and consistent enough for us to use to provide context to our lives. But we could just as easily use tides, the motion of the planets, phases of the moon. a heartbeat, weather patterns, etc. Any sort of regularly recurring event – again, time is simply our way of making sense of *motion*.
People have gotten used to accepting time as a physical, independent entity, that has its own substance, only because this has been so useful to us. But time is relative: the closer one gets to the speed of light, the more time slows down. If were you to travel at light-speed for one year, you would age one year, but centuries would have passed for everyone else no traveling at that speed.
Time is simply motion.
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