Is gravity a force or not?

  • #26
jtbell
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I thought the geometric models of space time were simply mathematical cheats for calculating gravity and not actual geometry based on what space time is. Yes? No?
How would we tell the difference?
 
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  • #27
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What does this mean? "Phenomena in nature" are physical. So is spacetime. So is whatever quantum "stuff" underlies spacetime.
Can I just leave it there? More discussion on my comment will bring in a huge elephant into the room and I do not have enough weapons to defend the animal. I'll clearly lose the argument in a minute.

It came from my simple observation that everything in the universe, matters, particles, living things, have a survival instinct. This can not be formulated in any type of mathematics or well defined laws at this time.
So, I surrender. My comment was simply offered as food for thought.
 
  • #28
PeterDonis
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It came from my simple observation that everything in the universe, matters, particles, living things, have a survival instinct.
You do realize that elementary particles can be created or destroyed in various interactions described by quantum field theory, right?
 
  • #29
Nugatory
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I was under the assumption that time dilation could occur from an energetic event.
Time dilation happens any time that two observers cannot find a single unequivocal and universe-wide standard for "at the same time" - and as Einstein's relativity of simultaneity thought experiment with the train demonstrates, all that's necessary for such a standard to be impossible is that the observers be moving relative to one another.

The easiest way to see that time dilation emerges from relativity of simultaneity is to consider that the statement "A's time is not dilated relative to B's time" is equivalent to "if, at the same time that A's clock reads noon B's clock reads X, then at the same time that A's clock reads 1:00 PM B's clock will read X plus one hour". The appearance of the phrase "at the same time" tells us to be watching out for relativity of simultaneity. (Note also that relativity of simultaneity explains how A's clock can be slow relative to B's clock yet B's clock can also be slow relative to A's clock).

Gravitational curvature is just another thing that interferes with our ability to find a single universe-wide standard for "at the same-time" and hence leads to time dilation.
 
  • #30
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I do enjoy reading threads like this one. Even more in another physics forum a gentleman seems to spend his time just contributing to this forum. When he commented on a concrete questions his physics knowledge became evidently smoke! Why am I writing this?

Physics and when it deals with concept alien to our day-2-day experience like quantum and relativistic theories, when it deals with cosmology, it wakes in us aficionados an avalanche of thinking and reflection! But I like to get back to basics with 2 statements that I believe explain what I mean!

1. As expressed here in this thread a couple of times, the physics science does not claim to say what is real! Physics works with models whose quality is given by how well they predicts what we perceive in experiments and observation through measurement.

2. The only language that gets us to speak the "same language" in physics are "mathematics"! If we do not speak this language we are like an analphabet who wants to grasp the wealth of Shakespeare by just being able to grasp the images of a printing with pictures! Mathematics are the language that allows us to express us about alien concepts with the smallest amount of ambiguity!

So as a kid in school first has to learn to read and write so that our civilization becomes accessible to him, same is true with Physics. Learn the mathematics and then start to "read" what is available about a topic in physics. The good think of this day is that you do no have to become a mathematician expert in applying mathematics, but proficient enough to be able to "read" mathematical notation understanding the principles of the applied mathematical tools. A tool like Mathematica from Wolfram Software can help you to "apply mathematics", but you have to have a certain knowledge about the mathematics involved! Both to read mathematical "text" and grasp what is said, as to "apply mathematics" using a tool like mathematica and its solvers!

To learn this mathematical concepts a very valuable tool are the courses available for free from the MIT in Boston via its "OpenCourseware" offering.

I am applying this to myself, even as I do enjoy the course videos about Cosmology and Inflation available at OCW, even while enjoying the reading of books like "The first three minutes from Steven Weinberg ot the one from Martin Reese, Just Six Numbers! As fascinating such readings are, it is just like watching picture in a comics books. You grasp what is being presented, but you are unable to "judge" the quality of the concepts presented nor are you able to understand and judge by yourself what is justifying opposing models and theories!

The result are tons and tons of reflection from readers that try to interpret the "pictures" they have seen and express what they guess they have understood using the highly ambiguous "normal language", like english in this case! After reading this kind of thread contributions I get bored and the feel of loosing my time. The writers should invest their own time to learn, so that then they might be qualified to discuss the topics and use the valuable time of others, or they are already having in mind to be exchanging ambiguous contributions with people equally qualified, in this case reading such a thread is waste of time!

Why do I waste my time? I am of the generation that believes in "evangelism" as a mean to "educate" the market!
 
  • #31
Nugatory
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This thread has wandered far from its origins... Time to close it.
 

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