I have spoken about time and gravity in my previous posts, time and time again. They both or at least one of them somehow pops up in every science article one way or another. In fact, It would be impossible to do any physics without one of them being a key aspect or a key player in any physics.
Are they fundamental or are they emergent from something else, however? We don't know for sure, but we do know that they are both closely related to space, in other words, they are related to matter, which is essentially energy!
Gravity, despite it seemingly being very intuitive and natural in our daily lives, has been one of the big issues in physics for a long time. Physicists have tried to make it fit in with the other forces in nature one way or another, to unify those forces and to arrive at a unified theory, but so far, none have been very successful.
Maybe we are getting the wrong answers because we asked the wrong questions. Never hurts to ask them, but as we will see in a bit, gravity does not seem to be a force, and it appears to be only an effect of the curvature of spacetime!
Time has been unified with space. Those two are inseparable in a continuum we now call spacetime. Time used to be thought of as unchanging, flowing everywhere all the same and at the same rate. And this has some merit for a solitary observer. For such an observer, a clock will tick for him at the same rate regardless of what he is doing or where, a rate of one second per second.
Once you have two clocks and start comparing, however, things would change. Each of those clocks would be ticking differently under different conditions. If one clock for example is stationary and the other is moving fast, the fast moving clock would experience a slightly slower amount of time passing compared to the stationary clock. This is what we call a time dilation from the special theory of relativity.
Moreover, time being part of the spacetime continuum, its flow would also depend on how space is curved between two locations, in General Relativity, it corresponds to the strength of the gravity experienced at a particular location.
Gravitational Time Dilation:
Imagine we have a very tall building that sticks out into outer space, at the ground floor we send a photon towards the top of the building. Timing the sending of the photons at exactly 1 second intervals.
At the roof of that building we place a receiver with a clock to detect those photons.
The Pound–Rebka experiment was one of the first experiments to test and confirm experimentally the existence of Gravitational time dilation in 1959, followed by others with refinements and increased precisions.
Time dilation is the reason why we have to adjust the Global Positioning System (GPS) we have, without such adjustment, the GPS system would fail really quickly. If not for those adjustments, a location would have an error of about 10 kilometers (about 6 miles) within just a day of running it.
The crazy thing about gravitational time dilation is that it doesn’t come from gravity, the gravitational attraction (gravity) is actually caused by it. And this is in fact the connection described by Einstein's field equation between mass/energy and spacetime.
The cause of the time dilation is the mass (That would be Earth in our example above). It directly causes the time dilation which causes the observed behavior we call gravity.
How gravitational attraction gets caused by time dilation:
As we already know, gravity makes things (mass) clump up together, and the more mass clumped up together the stronger the gravity becomes. And here’s basically how that gravitational time dilation works to produce that observed effect of gravity:
Imagine an object like a ball floating right above the ground with no other forces acting on it, and let’s forget gravity for a second. In such an example, there would be no reason for that ball to fall. Practically, Newton’s laws of motion apply to it, no unbalanced forces mean no acceleration, and that means if the ball wasn’t already moving it will not start to move, so the ball just floats there.
So, if we attach 2 clocks to that floating ball. One to the top of it, and another to the bottom, they will be ticking at different rates too, the difference is extremely small, but there’s a difference and that will do no matter how small it is. If we graph this on a 2 dimensional diagram considering only the up and down direction for the space direction, and the time for the sideways direction. The ball should only be moving in the time direction on that diagram, without any change for the space direction, but that wouldn’t be the case!
What would actually happen, is that the clock for the top of that ball would be ticking slightly faster than the clock for the bottom of that ball. This in turn would cause the top of that ball to move a tiny bit faster than the one at the bottom (which is closer to the Earth). This gradually turns the motion arrow of that ball, what is called the Four-velocity, pointing more and more towards the Earth over time. Forcing the ball’s movement in space towards the ground, or in other words, making it fall to the ground simply because of that time dilation!
As long as time passes at different rates in different places, there will be gravity. It exists without treating it as a force. Gravity is an effect of spacetime curvature, the ball falls to the ground because there is a flow gradient in time. Same thing with say the moon orbiting Earth or a planet orbiting a star. The flow of time around objects is slowed down.
All those massive objects aren't exerting a force, time just passes slower nearby them, creating a gradient in the flow of time, which bends spacetime paths.
Time is the cause of gravity!
● Thank you for reading ●
● •1- Spacetime | 2- Gravitational time dilation | 3- Newton’s laws of motion | 4- Four-Velocity |
© 2022 @yaziris.
Wow, you really explain things very clearly! I'm used to being a bit confused by the physics posts written here.
And time actually causing gravity?! Fascinating way to look at it!
Thank you! It's what I try to do, glad to hear I'm somewhat succeeding in that :)
And yes, even the simple concept of "spacetime" is not that easy to fully comprehend. Usually the focus is on the curvature of space, but it is time that is curving too and the effect we see as gravity is caused by it.
Thank you again for stopping by and for the nice comment!
I'm really eager to see a physicist weigh in on this. However, as a simply ordinary person who skipped physics in high school (and calculus) let me say I loved this blog. It made perfect sense to me. I understood the business about the ball moving, and time dilation. Because I am a humanist (actually have a degree in the humanities 😅) I see the effect this information has on our concept of reality.
When people say "God is Dead" what they often mean is the old rules don't apply. Everything we thought was fixed and certain about the universe, is not. As you show in your blog, there are rules, but they are new. And not all of us understand them. Before, we thought we knew why apples fell to the ground and we believed we knew that the earth and the moon were fixed in their orbits and in their relationship to each other. Now we have time dilation...and unanswered questions.
The effect on literature, on our psyches...immeasurable. You write this beautifully. As you can see, your exercise is provocative. Great blog.
Thank you so much for this amazing feedback @agmoore,
The whole thing about what we call "reality" is as weird as it can get. The weirdness is not limited to the quantum world, but we are familiar with what we see and feel in our daily lives, so we don't see things as "weird".
I've written a while ago about spacetime curvature and what is called geodesics. But when we talk about curvatures and paths, usually it's easier to imagine those as related to "space". In this article, it was about emphasizing that it is Time that is curving too. And of course mass/energy causes it all.
I think it's safe to say "no one really understands them". We might know about them, but understanding them is a different thing.
It might be actually. Superdeterminism does a very good job showing how everything is predetermined but that theory is impossible to prove or disprove.
Happy to hear that. 😊
And again, thank you so much ❤
What an interesting explanation. Your explanation aside, do you think the reason scientists haven't solved what gravity really is, is due to mathematics or lack of thinking outside of the box?
It's a bit easier to comprehend space time curvature on a planetary or star scale, but a ball on the surface of Earth is harder to grasp. Is space time more warped where we live, the planet's surface?
Oh, they have. However, unifying it with the other forces (the weak force, strong force, and electromagnetic) has been a problem. So, they try other ways of looking at it to hopefully get it to fit in with those other forces and have a unified theory.
Yes indeed. Spacetime is more curved the closer you are to mass, and the more mass there is. You would weigh a tiny bit less at the top of a mountain or at the top of a skyscraper, than on sea level, for example.
Thank you for your nice comment and for those questions!
Holy crap I am jetlagged and see I wrote "time space".
It's been a while since I read anything about unified theories, but is M theory still being considered as a unifying theory?
That's fine, basically the same thing :)
As far as I know, M-theory is a unifying theory for superstring theories, with multiple dimensions, etc. It has no evidence to support it, however, and no complete mathematical formulation.
But yes, it's one of those attempts I mentioned earlier, though it builds on string theories which generally aren't in much favor.
The main issue is that gravity does not fit well with the quantum world. Therefore, at the level of elementary particles, it is tricky to include gravity. This is a whole field of research on its own, and a lot of progress has been made over the last decades. However, the problem is not solved yet (will it ever be?).
Once again, I am a bit late in commenting this post. Sorry about that, but week-end moments are precious family moments that bring me quite offline. Anyway, here I am.
I will start to ask you a question. Do you believe in coincidences? I may start to… More seriously (don’t worry, coincidences are just coincidences in my opinion), I started to smile a lot when I red the following:
I am in charge this year of a special course where students in their first year of bachelor studies in physics can approach state-of-the-art research in various sub-fields of physics. On top of attending (dedicated) scientific conferences on various topics, they have a bibliographical project to handle and that should include some calculations that they have to (re-)do.
One of the topics that were proposed this year is precisely about the Pound-Rebka experiment (that is understandable enough for a first-year student)! The defence is scheduled in 9 days. I will let you now how it will be if you are interested ^^
Cheers!
Don't worry about it, family is always first! I hope everyone in your family is doing fine and recovering well.
As weird and "unscientific" this may sound, but I do think there's something that makes people behave like a wave. 😆 Everyone somehow tends to start bringing up similar subjects and do similar things even though each one of them is completely disconnected from the others.
I think it might be something with the subconscious, subtle stuff we see or hear sparks ideas and we end up talking about them in a similar way.
Crazy talk aside, yes, I am interested. Let me know how it will be. 😁
My wife has fully recovered, and my son is still a little bit positive (the self-test returned a fainted marker today). We are finally getting out of it, and I managed to stay dark and undetected (beware of the physicist's joke). At least for now... ;)
I will definitely let you know (don't hesitate to ping me if needed)! :)
wow...
Wow indeed! 😁
Appreciate you stopping by BroDude.
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STOPCheck out the last post from @hivebuzz:
This is a mind bending theory. I have to admit that I have a difficult time grasping it. I understand it in principle, but I just can't groke it. I first came across it in the following youtube video, and I was delighted to read your explanation:
Relativity is by far, the most successful theory that actually describes reality. Reality is mind bending indeed. 😁 I've seen that one before. I like that guy's videos, informative with timelines and backgrounds about the subjects. Here's another one about this subject that I've seen, if you like watching physics vids.
Thanks for stopping by! :)
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