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Author Topic:   Quick Questions, Short Answers - No Debate
frako
Member
Posts: 2823
From: slovenija
Joined: 09-04-2010


Message 166 of 569 (618878)
06-06-2011 9:41 PM
Reply to: Message 163 by Taz
06-05-2011 5:05 PM


Re: swallowing drugs
There is no documented case of overdose by marijuana, so he should have been fine. Yea you can eat marijuana though its better to make cookies from the stuff though i dont like them too much of a delayed reaction and when it hits you it usually hits you like a train from nowhere.

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ProtoTypical
Member
Posts: 1793
From: Ontario Canada
Joined: 08-04-2010


Message 167 of 569 (631505)
09-01-2011 12:20 PM


Lagrange point
Is there such a thing as a Lagrange point for a photon near a black hole? Do photons ever orbit anything?

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Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 168 of 569 (631512)
09-01-2011 1:51 PM
Reply to: Message 167 by ProtoTypical
09-01-2011 12:20 PM


Re: Lagrange point
Similar question: can there be a Lagrange point which is a black hole? Suppose you had one black hole orbiting another, would its Lagrange points also be black holes?

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cavediver
Member (Idle past 1982 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(2)
Message 169 of 569 (631520)
09-01-2011 3:10 PM
Reply to: Message 167 by ProtoTypical
09-01-2011 12:20 PM


Re: Lagrange point
Is there such a thing as a Lagrange point for a photon near a black hole? Do photons ever orbit anything?

Good questions. Answers in reverse order:

For the basic Schwarzschild (non-rotating, non-charged) black hole, there is a photon orbit 50% further out than the event horizon. If you were to stand at a point on this orbit and look tangentially to the black hole, you will see the back of your head Plus an infinite number of repeats disappearing into the distance. If you build a hollow tube space-station around the black hole and centre it on the photon orbit, the tube will look straight to anyone on the inside. If the station is placed inside the photon orbit, it will look curved again - only it will curve away from the black hole!!

Now a Lagrange point is a very specifically defined concept within Newtonian Gravitation, and it doesn't readily apply to photons - but, if you are simply asking if there is a place in the vicinity of a black hole where a photon can remain stationary, then the answer is, yes! In fact, owing to the spherical symmetry of the black hole, there must be an entire sphere of these places. And this sphere is our infamous event horizon. The horizon is actually a (spherical) sheet of trapped photons. What is more, this must mean that the horizon must be travelling at the speed of light - and it is. In fact, all of the relativistic effects around the black hole that you call gravitational, can just as easily be understood in terms of relativistic velocity.

I guess any more than that would really need its own thread... and my chilli salmon is calling.


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ProtoTypical
Member
Posts: 1793
From: Ontario Canada
Joined: 08-04-2010


Message 170 of 569 (631521)
09-01-2011 3:18 PM
Reply to: Message 169 by cavediver
09-01-2011 3:10 PM


Re: Lagrange point
Mmmmm...salmon.

Thanks cd, I will go read some more.


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Dr Adequate
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Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 171 of 569 (631533)
09-01-2011 5:09 PM
Reply to: Message 169 by cavediver
09-01-2011 3:10 PM


Re: Lagrange point
Now do mine. Pretty please?

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cavediver
Member (Idle past 1982 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(2)
Message 172 of 569 (631535)
09-01-2011 5:19 PM
Reply to: Message 168 by Dr Adequate
09-01-2011 1:51 PM


Re: Lagrange point
can there be a Lagrange point which is a black hole? Suppose you had one black hole orbiting another, would its Lagrange points also be black holes?

When well separated, black holes behave just as normal gravitating objects. If you squash the Sun down to within its Schwarzschild radius, it will collapse to a black hole, but the Earth will continue to orbit as normal. And if you then squash the Earth down to a black hole, the moon will continue to orbit, without any change. And the Earth-Sun and Earth-Moon Lagrance points will be unaffected.

A small black hole can certainly find itself located at (or orbiting around) a Lagrange point, just the same as any test mass.

Two black holes in binary orbit that are close enough for us to wonder about their effect on their own Lagrange points are almost certainly in the midst of ultra rapid spindown towards merging, throwing out enormous quantities of gravitational radiation. As the black holes merge, the local space-time becomes highly chaotic, and the Lagrange points simply get caught up in the maelstrom. Eventually, things settle down to (most likely) a spinning Kerr black hole.


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Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 173 of 569 (631566)
09-01-2011 7:22 PM
Reply to: Message 172 by cavediver
09-01-2011 5:19 PM


Re: Lagrange point
When well separated, black holes behave just as normal gravitating objects. If you squash the Sun down to within its Schwarzschild radius, it will collapse to a black hole, but the Earth will continue to orbit as normal. And if you then squash the Earth down to a black hole, the moon will continue to orbit, without any change. And the Earth-Sun and Earth-Moon Lagrance points will be unaffected.

In which case their Lagrange points would not start behaving like black holes. But could you have Lagrange points that did?


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crashfrog
Inactive Member


Message 174 of 569 (631573)
09-01-2011 7:40 PM
Reply to: Message 173 by Dr Adequate
09-01-2011 7:22 PM


Re: Lagrange point
But could you have Lagrange points that did?

Could you have teapots that acted like orange trees? I'm pretty sure that L points and black holes are two different things.


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cavediver
Member (Idle past 1982 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 175 of 569 (631578)
09-01-2011 8:03 PM
Reply to: Message 173 by Dr Adequate
09-01-2011 7:22 PM


Re: Lagrange point
In which case their Lagrange points would not start behaving like black holes. But could you have Lagrange points that did?

I'm a bit confused by the question. If you are asking whether L4 and L5 could ever have a potential gradient so sharp that it creates a trapped surface and possibly an event horizon, then no, I am fairly sure that could not happen. That is why I mentioned the binary merger - that would create the most extreme potential gradients around L4 and L5. L1-3 are of course saddle-point unstable so they don't even act like gravitating points.


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Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 176 of 569 (631612)
09-02-2011 12:26 AM
Reply to: Message 175 by cavediver
09-01-2011 8:03 PM


Re: Lagrange point
If you are asking whether L4 and L5 could ever have a potential gradient so sharp that it creates a trapped surface and possibly an event horizon, then no, I am fairly sure that could not happen.

Yes, that's what I was asking. If it can't happen, then I guess the universe was weird enough already.

Edited by Dr Adequate, : No reason given.


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Portillo
Member (Idle past 2500 days)
Posts: 258
Joined: 11-14-2010


Message 177 of 569 (633704)
09-15-2011 5:37 PM


How many members does this forum have?

And the conspiracy was strong, for the people increased continually - 2 Samuel 15:12

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New Cat's Eye
Inactive Member


Message 178 of 569 (633705)
09-15-2011 5:39 PM
Reply to: Message 177 by Portillo
09-15-2011 5:37 PM


How many members does this forum have?

Top left, just under the banner:

quote:
Welcome, Member Catholic Scientist! [ Logout ]
EvC Forum active members: 269 (6958 total)

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Theodoric
Member
Posts: 6879
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 3.3


Message 179 of 569 (633711)
09-15-2011 6:30 PM


Message system
Can suspended members send and receive messages?

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fearandloathing
Member (Idle past 2484 days)
Posts: 990
From: Burlington, NC, USA
Joined: 02-24-2011


Message 180 of 569 (633714)
09-15-2011 7:18 PM
Reply to: Message 179 by Theodoric
09-15-2011 6:30 PM


Re: Message system
I think so, I know they can PM admin.

"No sympathy for the devil; keep that in mind. Buy the ticket, take the ride...and if it occasionally gets a little heavier than what you had in mind, well...maybe chalk it off to forced conscious expansion: Tune in, freak out, get beaten."
— Hunter S. Thompson

Ad astra per aspera

Nihil curo de ista tua stulta superstitione.


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