What really is “time”? (part 1 of 2)
The first ever picture of a black hole might have triggered questions about “life, universe and everything” in a few of us. It did in me.
Since I spend an enormous amount of time trying to build a vehicle that will help take objects a little further out of earth’s gravity well, I decided I will sit down and write about my understanding of earth’s gravity well.
This is a two piece blog.
The first piece will be about my understanding of the Special Theory of Relativity — the one that proposed that “the flow of time” is a relative quantity. The second piece will focus on my interpretation of the General Theory of Relativity — the one that proposed that “gravity is not a force but a geometric feature” of space-time.
INTRODUCTION:
The key to understanding special relativity is trying to understand and think about what ‘flow of time’ actually is.
The illusion of considering time as an independent physical quantity that marches along steadily, irrespective of what anything or anyone does is basically the curse Newton cast on all of us. It is a stubbornly persistent illusion that proves right for most of our day-to-day activities. And hence, the concept about time flow being relative is so hard to grasp. It plays right into what human consciousness is — a set of patterns based on a reference system that maps into and on itself. So, let me talk about reference systems.
THE NEED FOR A REFERENCE SYSTEM:
Philosophically and scientifically, everyone needs a frame of reference. Something that doesn’t change with respect to which all other changes are measured. In fact, measurement by definition is fundamentally valid only when you have a starting point and you quantify changes with respect to that starting point.
MEASUREMENT OF TIME:
Now let us think about time. What is time in physics? As in.. How do we know an event happened at 10 AM? Let us say — you saw a device(basically a clock that the world as a whole has standardized) pointing at 10 AM. Now you also see a friend of yours standing next to you at 10AM. So, this event of you standing next to your friend has occurred at 10AM. Simultaneity is key to saying two events — ‘clock moving to 10AM’ and ‘friend arriving’ happened at a certain point in time.
So essentially we have a system of reference that we humans fixed as constant. Nothing changes it. And now all events are compared to it. Convenient for measurement right?
LACK OF EXPERIMENTAL EVIDENCE:
But no known observation exists to categorically prove time is absolute. It is just a human-made absolute, frozen reference system. Defined precisely to be that — frozen. But that should make one think.
We don’t directly perceive time flow. We just measure it based on a standard we set. How can it be so absolute? More importantly, if we observe a quantity (measured speed of light) that seems to be explicable only when time is relative will we be willing to let go of our old “frozen” assumptions of time flow? Or will we just say everything that doesn’t concur with constant time is incorrect.
NEWTON CALLING FOR A ‘GOD’:
In fact, even Newton had a problem with this. I have read articles that suggest he was not happy with just assuming time flow as a constant while developing calculus. No physical evidence existed to prove time’s constancy. Imagine how apparent this assumption should have been to the very creator of differential calculus!
He was in pursuit of explaining changes & how quantities change with respect to another. But there was nothing that could be frozen. How would calculus work?
Newton invoked God’s hand here and said “God takes care of time”. We can take care of the rest. In fact, I think, that’s why his paper on his 3 laws was called the ‘principles of mathematics of natural philosophy’.
THE PROBLEM WITH THE ABSOLUTENESS OF TIME FLOW:
A) Every experiment ever conducted showed that the speed of light is always the same. Ether, which humans again created, because we were desperate for a reference system, was not detectable. Also, if we moved relative to ether and measured the speed of light relative to ether, as we moved, we still got the same number for the measured speed of light. (In fact we were so desperate that we said ether was magical. If we moved with respect to it, “it” knew about our movement and adjusted itself. This is what Lorentz proposed and he precisely came up with all the equations Einstein did but his theory needed ether to be magical and almost have a brain of its own. This is why we call the length contraction and time dilation equations Lorentz transformations. His formulae were right. His theory seemed flawed for non believers in magical ether. )
B) Although, measurement of speed is always relative and with respect to something. So if an object is moving, its speed can only be determined with respect to another object.
So, measurement of speed is always relative BUT the measured speed of light with respect to anything else (moving or otherwise) always came out as a constant experimentally — a contradiction!
FINALLY, LETTING GO:
So, the absoluteness of time had to be questioned & that’s what Einstein did. Instead of freezing the manner in which time flows, he proposed freezing the ratio of distance covered by electromagnetic radiation in a given time period to that time period itself as a constant.
This helped! Time flow could be adjusted to explain the constancy of the speed of light.
If you come to think about it — this is actually not a bigger change or assumption than the assumption that time flow is absolute. This is just another human-made assumption. That’s all.
When no one (such as Lorentz, Michelson-Morley) could let go off a reference system that explained everything before him/her, Einstein did. This is where he stands out.
HOW DOES THIS FRAMEWORK HELP?
This assumption/ framework:
A) explains everything without ether. No magical, omnipresent substance was needed and it did not have to adjust itself to keep the speed of light a constant. Time just flowed differently based on when and how you measured it’s flow. That’s all!
B) doesn’t destroy Maxwell’s equations because those equations can’t hold true if light did not move. Okay, wait! But when will light not move? Einstein imagined himself traveling next to a light beam at the speed of light. For him, at that speed, if he looked next to him, light should have been just static vibrations, right? Speed of light should have dropped to 0 (relatively speaking). Light was not propagating! If this were possible, Maxwell’s equations fail to explain phenomena when traveling at the speed of light. Isn’t it easier to just say, the speed of light is a constant but instead, when you are traveling at the speed of light, time flow stops for you and that’s why light seems to not propagate?
C) allows simultaneity to be limited by the concept of observation. If a lightning struck a point I was standing at, I will see a clock and say it happened at 10AM. Another person in a train speeding away from me will say it happened at 10.0000001 AM because he was traveling away from me. The occurrence of events simultaneously is governed by the ability to measure their occurrence simultaneously. Consider the limiting case of this experiment. Lightning hits me at 10AM. You are traveling away from me at the speed of light. Now you will never see the event. Will you? Information about lightning hitting me will never reach you. You are running away from information about the event at the same speed that the information is coming to you. So, according to you this event has not occurred. Now, you can explain the non-occurrence of this event (for you) in two ways:
- time stopped for you but speed of light is constant. Since time stopped you are stuck in the past. The event did not occur for you, yet.
(or) - time is moving as usual for you but the speed of light relative to you is zero. Hey! but we know no observation exists to prove light’s speed is relative.
So the first explanation makes more sense.
CONCLUSION:
Saying the speed of light is a constant and is a maximum is just another way to define and freeze the maximum speed at which information of any kind can be propagated in our universe.
Some fun thoughts to leave you with…
CASE 1:
speed of light = distance travelled by light = 300,000km/ 1 second.
And if in a pre-Einstein world, you, in that 1 second (an arbitrary number you are stubbornly not willing to change), travelled a greater distance than light (say 400,000 km) and abruptly stopped.
Then…
To the rest of the world which (a) can only measure light at one constant speed and (b) stubbornly measures one second as a particular constant unit of time flow,
… you still travelled at the speed of light! (to detect your presence 400,000km away light will have to come back and it will take 4/3 seconds each way. 400,000/(4/3) is still 300,000km/s)
CASE 2:
In an Einstein-ian world -
Light speed is a constant and a maximum. Time stops for a person traveling at the speed of light. This system of keeping time breaks down in trying to explain your faster than light move because
(a) you and light started simultaneously and
(b) you reached the 400,000 km point before light did, and for light, because it is moving at light’s speed, time did not even move when it got to you.
… you ‘already had to be there’ to account for this. Or you went to the past.
Negative time is a mathematical construct. If positive time is forward, negative is backward but it doesn’t mean anything about the past except in the sense of ‘having already been there’.
