
#1
Jun2211, 05:59 PM

P: 1

Hi every1
My question is: we know nothing travel faster than light. Gravity travel at the speed of light, right? Now: light cannot escape from a black hole. So: gravity cannot escape from a Black Hole. Then... why can we feel the gravitational field of a black hole if gravity cannot be transmitted outside the black hole?? Imagine that the black hole suffer some change: it eat some other black hole or ver big star... the gravity field will change. But if gravity travels at the speed of light and light cannot escape from a black hole... how could we feel the change of the system? Thanks!! 



#2
Jun2211, 06:12 PM

Sci Advisor
Thanks
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#3
Jun2311, 02:44 AM

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#4
Jun2311, 03:02 AM

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question about Black Holes (simple question) 



#5
Jun2311, 03:59 AM

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#6
Jun2311, 04:44 AM

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#7
Jun2311, 05:16 AM

P: 1,115





#8
Jun2311, 02:43 PM

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#9
Jun2311, 02:47 PM

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#10
Jun2311, 04:09 PM

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#11
Jun2311, 04:16 PM

P: 315

Also, as is discussed over in the quantum physics forum, it seems to be generally agreed upon that virtual particles have no reality. They are just mathematical artifacts that arise from solving an equation perturbatively.




#12
Jun2411, 03:33 AM

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#13
Jun2411, 03:34 AM

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#14
Jun2411, 03:35 AM

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#15
Jun2411, 03:36 AM

P: 1,115

EDIT: A clarification  'utterly fails' above is not meant to imply any disproof of QFT, virtual particle exchange picture etc  rather the logic of two way dynamical communication fails a la BH EH re 'outside' contact. 



#16
Jun2411, 04:07 AM

Emeritus
Sci Advisor
P: 7,433

Well, you'll have to find someone who understand virtual particles better than I do if you seriously want to use them and be sure you're actually getting senisble results. And your best bet on finding such a person would be on some other forum, because classical GR doesn't use them. You might get lucky and find someone on this forum who can do it, and if you're even luckier it'll be understandable.
I suspect about 99% of the people who use the virtual particle model expect them to behave exactly like real particles, and it's obvious they don't  for instance all the usual arguments about abberation. However, from my limited understanding from just reading the FAQ's, virtual particles are unphysical enough to be faster than light, i.e. the lines on the Feynman diagram may apparently be spacelike lines. What voodoo makes the diagrams work with spacelike lines isn't clear to me (assuming I"ve understood correctly in the first place), but since it is clear that the virtual particles don't actually carry any information, it wouldn't violate any physical laws. Meanwhile, there are lots of subtle aspects to the classical picture, including the whole idea of "force". 



#17
Jun2411, 04:48 AM

P: 1,115

To buttress that, here's a further example of where redshiftisjustopticaleffect just doesn't cut it imo. Suppose we drop towards a BH a beacon having a given rotational speed about an axis coincident with the radial ordinate, and let's say it emits a linearly polarized beam of light radially outwards  back to some fixed external observer. On the beacon's way down to doom, the returned beam is not only undergoing redshift, but the rotation speed of the polarization vector is also slowing. I say both redshift goes to infinity AND polarization rotation cease at the EH. The latter in particular is speaking loudly to me re the consistency of *any* kind of exchange process. It ceases re external observer  period. Now if I have this all wrong then fine I will eat humble pie, but that would require some penetrating and detailed logical counterargument. 



#18
Jun2411, 06:26 AM

Mentor
P: 16,470

If you think one of your claims has merit and that it is being ignored then you should start your own thread. Otherwise don't take a lack of response as indicative of anything. 


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