# Why two mass attracts each other?

Discussion in 'Physics & Math' started by hansda, Mar 19, 2013.

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1. ### ash64449Registered Senior Member

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Handsa, as i have already said, gravity is always attractive because acceleration is indistinguishable from gravity.
As acceleration is indistinguisable,we can say that acceleration is same as gravitational field,or field that is attractive. Note that you cannot show acceleration to be repulsive and thats how it answers your question.

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5. ### ash64449Registered Senior Member

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no. Only when your 'real time' changes,is when time meaured by clocks changes.

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8. ### ash64449Registered Senior Member

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well,i think by 'real' time,he is talking about proper time. And indeed proper time dosen't change as it is the part of time-like invariant interval between two events.

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11. ### eramSciengineerValued Senior Member

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It's kinda amusing to watch hansda and ash argue

12. ### Guest254Valued Senior Member

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Well I think that settles it! Professionals (and I'm being presumptuous enough to speak for scientists in general) have a very different notion of what it means to understand a theory of physics than you do.

In my mind, when you really understand something you don't really need to remember much! For instance, for my sins I have to give a GR class from time to time, and I would never recommend the students simply try to learn, verbatim, the lecture notes - I would simply ask that they understand them. Any student that managed to do that (say a mid 2:1 student) would certainly be able to reproduce a lot of basic GR (geodesic equation, variation if Einstein-Hilbert action, derive Schwarzchild solution, get physical conservations laws via Killing vectors....). I would also guess that they wouldn't proclaim their understanding of the subject is better than professional researchers!

13. ### brucepValued Senior Member

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That's not true. Gravity can be repulsive when the 'pressure term' in the cosmological metric is dominant. Essentially that's how our universe began as an inflating soliton.

14. ### brucepValued Senior Member

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What kind of a sin could that possibly be? Seems like it would be an honor expounding on such a theoretical model. I'm impressed.

15. ### Guest254Valued Senior Member

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The "for my sins" comment probably needs a qualifier. I don't mind teaching in general (I actually quite like teaching some students), but for the most part I'd rather be working on my research.

16. ### brucepValued Senior Member

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I figured as much. Tell me something about your field of research. So I can do some reading. Good luck in your future.

17. ### Guest254Valued Senior Member

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My research is in mathematics (currently semi-Fredholm theory for nonlinear eigenvalue problems).

18. ### brucepValued Senior Member

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I expect the reading won't do me much good. Still fun. Thanks Guest254.

19. ### hansdaValued Senior Member

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If "time measured by a clock" is "real time" and gravity/spacetime causes 'time dilation' for "real time"; that means 'time reversal' is possible.

There is no evidence of 'time reversal'.

So, "time measured by a clock" can not be "real time".

20. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

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Is English a second language?

21. ### hansdaValued Senior Member

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You speak science. Where is the problem?

22. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

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The problem is you're not speaking science.

It's speculation and fiction.

23. ### hansdaValued Senior Member

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Well, what evidence you want? 'Experimental evidence that "time reversal" does not take place' - will it do for you?