Why do objects rest on space thus causing gravity?

[nitsuj]

I don't think time would pass for you at all. You'd become "timeless" if everything in you and around you stopped moving...

That's the same "trian of thought" I went on when thinking of time.

Likely now is a good time to gain an inderstand of how time is a geometric property, and not a measure of "happenings" (contrary to your understanding that for something "frozen" time has stopped). My mechanical watch slows or speeds up depending on temperature, of course temperature has lots to do with motion, has nothing to do with ensuring the "passing" of time.

Another angle is to consider all our clocks are imperfect, they all have accuracy issues to some degree as they measure "happenings". It maybe helpful to check out an idealized clock such as the "Light Clock", it's a pefect clock that doesn't exist and relies on the relation of space & time with respect to c; not on "happenings" per se but on known laws of physics...specifically the geometric property of time.

 

[wabbit]

I don't think time would pass for you at all. You'd become "timeless" if everything in you and around you stopped moving...

Your view echoes that of Aristotle, roughly "time is a measure of change". I don't think it's wrong, though the idea of something that doesn't change at all, and therefore doesn't interact in any way with anything else, is probably outside the scope of physics.

Still, if we inhabited a completely static universe, then the time coordinate would be unphysical and there would be no meaningul notion of time.

This is of course not our actual universe. However, if we supposed a patch of our universe to be perfectly static (which I think we might conceive of hypothetically in classical mechanics though perhaps not in QM), then the physics of this patch could be described without a time variable, and in that sense, time wouldn't exist within this patch.

Of course observers outside that patch would still assign to it a time coordinate, and would just say that the patch is static - or would they? they would be unable to interact with that patch, hence to measure its properties, so perphaps they would just say that it doesn't exist - I suspect that to them it would be undistinguishable from a hole in spacetime.

 

[pervect]

No, I don't think you'd age if all your molecules, quarks etc. stopped moving.

You're rather missing the point. The point is that time passes. You might not "age" if someone threw you in a freezer (which could stop your molecules from moving, but it'd be doubtful if it would stop the quarks from moving. I'm not aware of any way to stop quarks from moving, and the whole idea is a distraction anyway). The point is that time would still pass, even if you were frozen and not conscious.

You are going from the past to the future, always. Space-time curvature is a rather abstract concept. It's relatively easy to visualize a curved spatial surface (such as a 2d surface of a sphere) The trick to understanding a space-time diagram is to realize that one spatial dimension on the diagram represents time and not space. The ability to do this should be familiar from the concept of a time-line, where events are put in order and represented by a spatial line. [add] An even better example is the common practice of plotting position versus time on a piece of paper. One axis of the paper represents "time", it is equivalent to a space-time diagram.

The difference from the rubber sheet analogy as usually presented is that the rubber sheet is purely spatial - nothing on the rubber sheet represents time.

 

[stevendaryl]

I think of time as just how rapidly or slowly things move with respect to other things (like clocks, photons, etc.)

Well, no offense, but that doesn't make any sense. You need the notion of time to make sense of the words "rapidly", "slowly" and "move". So it doesn't make any sense to define time in terms of those words. I mean, it's circular to do so.

 

[stevendaryl]

The way I think of time as another dimension just like space is in terms of "flip books". I don't know if you've seen those, but they are books with drawings on them, and the drawing on each page is just slightly different than the drawing on the previous page. So if you flip through the pages rapidly enough, you'll see an animated movie. The flip book is a 3-dimensional object that can be interpreted as 2-dimensional objects moving through time. If the animation shows a pebble falling to the ground, then on each page, the pebble is a point (roughly). But the collection of all the pages show the pebble tracing out a curved path in 3 dimensions.

Similarly spacetime id s 4-dimensional object that can be interpreted as 3-dimensional objects moving through time.

 

[nitsuj]

Well, no offense, but that doesn't make any sense. You need the notion of time to make sense of the words "rapidly", "slowly" and "move". So it doesn't make any sense to define time in terms of those words. I mean, it's circular to do so.

Yay philosophy!

 

[Soundmike]

I've heard it explained is that we are all falling.. everything, we fall to the earth, the Earth is falling towards the sun, the sun is falling towards the galactic centre...
to understand gravity maybe this would be helpful



and to get an idea of angular momentum counterbalancing

gravitational pull maybe this would be helpful



And to get an idea that space itself is flowing listen to what said about it when it reached a black hole



I don't get people on here making comments like "I'd need a mathematical equation to explain it" BS!
The cracker of a concept could be a beggar off the street who has the clarity to see blind to the nuts and bolts...
My favourite phrase.. explain it to me like I'm an 8 year old... but saying that if anyone wants to share mathematical equations with me on here it would be my please andn honour to learn your perspective

 

[Drakkith]

I don't get people on here making comments like "I'd need a mathematical equation to explain it" BS!

Typically the mathematical model used is very, very specific and rigorous, and understanding the math usually means you understand the theory without needing someone to 'translate' it into common language. In addition, many concepts are explained very well when you understand the math, but trying to explain the same concept without the math is extremely difficult and prone to confusion and misunderstanding.

For example, explaining the expansion of space is very hard to do if you leave out all the math. You need to bring in analogies like bread rising, balloons stretching, and others that give people the wrong ideas. If, instead, you focus on the math describing how galaxies move apart over time, it is immediately clear just what expansion means. No analogies needed. No misunderstandings.

A big part of the problem is that normal, everyday language is highly subjective. Many words mean slightly different things to different people (or sometimes even wildly different things). For example, if I told you, "I ran to the store earlier", what would that mean to you? Did I get in my truck and drive there? Did I literally run to the store using my own two feet? Did I call a cab or a friend for a ride? These questions could go on and on.

If I gave you a mathematical formula describing my position over time with respect to the store, there's little-to-no confusion there. And from that formula you could get several other properties, such as velocity and acceleration. Now, while this doesn't tell you everything that happened, such as which drinks I purchased or how I got there, it is very, very specific and accurate to what it does tell you.

An example specific to this thread is the description of gravity as one object falling towards another. If I'm falling towards something, that, to me, means that I'm approaching that object. For example, falling to the ground means my I'm moving towards the ground. But look at the Earth's orbit. Being an ellipse, this orbit requires as to be moving away from the Sun for half of the orbit. How can gravity be us falling towards an object if the distance between us and that object is increasing? Now, I'm sure you could write several paragraphs explaining exactly what falling means in this context so that you come up with a way to say that gravity is one object falling towards another. Or, you could forego everyday language altogether and use a math-based model which is much more exact in its language and makes numerical predictions that can be verified to great precision. I think I prefer the latter.

 

[Amrator]

I've heard it explained is that we are all falling.. everything, we fall to the earth, the Earth is falling towards the sun, the sun is falling towards the galactic centre...
to understand gravity maybe this would be helpful



and to get an idea of angular momentum counterbalancing

gravitational pull maybe this would be helpful



And to get an idea that space itself is flowing listen to what said about it when it reached a black hole



I don't get people on here making comments like "I'd need a mathematical equation to explain it" BS!
The cracker of a concept could be a beggar off the street who has the clarity to see blind to the nuts and bolts...
My favourite phrase.. explain it to me like I'm an 8 year old... but saying that if anyone wants to share mathematical equations with me on here it would be my please andn honour to learn your perspective

*Sigh* Where's Feynman when you need him?
If I could explain it to the average person, I wouldn't have been worth the Nobel Prize. - Richard Feynman

 

[Nugatory]

or all your implied mathematical understanding which I take for granted is extensive that you and others who have written here are unable to or unwilling to use the very words which helped you to learn these tools...

I'm having some trouble seeing the validity of this criticism. Further up in this thread we have this post which contains pointers to some of the best plain-English explanations that you'll find anywhere. You don't have to move past those videos to the rigorous mathematical formalism of general relativity if you don't want to, and you'll still have a perfectly sound understanding of how general relativity works.

Of course understanding how general relativity works is not the same thing as understanding general relativity at a level that allows you to solve problems in GR ("How do we expect the orbit of a planet to differ from the Newtonian prediction, and for which objects in the solar system will that difference be large enough to measure?") or to come up with new ideas about what GR means - for that, there is no substitute for working through the math.

 

[Nugatory]

I'm closing this thread, as the issues that are raised in the most recent posts (including my own reply) are best discussed in a new thread - we've answered the original poster's question in this thread several times over.