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Old Feb 25th 2018, 04:55 PM   #1
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Question about "bigger on the inside" space

I'm not an actual physicist right now, and I have no idea about anything relating to general relativity, but I saw some kind of paper on the internet somewhere titled "Calculations on space-time curvature within the Earth and Sun", and while I didn't understand any of the math behind it, it seemed to basically be saying that something about how general relativity works makes it so that the diameter of the Earth and the Sun, and I would assume all things with mass, is greater if you measured it from the outside than if you did it by measuring its circumference due to some kind of space curvature thing. The idea really intrigued me because I love stuff like that and I wanted to know if there's any actually reasonable truth to it, or if it's just a weird technicality thing that you would only understand if you were an actual physicist. I know that I probably sound stupid, but from my perspective, as someone who has absolutely no background in any kind of relativity, it sounded like the paper was saying that the Sun and Earth and black holes were "bigger on the inside", which is a really cool idea. But I haven't found any other references to the paper at all anywhere ever and I've searched for a while, and if I haven't ever heard of it then it probably isn't a revolutionary idea. I could provide a link to the paper if needed, unless any of you know what the heck I'm talking about.

I know this is probably the worst place to ask, and I'm just going to be bombarded with people telling me that this forum is no place for a normal human who doesn't already have a PhD, but I don't know where else to ask a question about physics that would have people more knowledgeable than me. Isn't it a good thing that I'm asking someone who I know knows better than me rather than assuming something? I'm just curious.
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Old Feb 26th 2018, 12:32 AM   #2
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Originally Posted by LlamaMama View Post
I know this is probably the worst place to ask, and I'm just going to be bombarded with people telling me that this forum is no place for a normal human who doesn't already have a PhD, but I don't know where else to ask a question about physics that would have people more knowledgeable than me. Isn't it a good thing that I'm asking someone who I know knows better than me rather than assuming something? I'm just curious.
Don't worry about what you know/don't know. If you have a question then ask!

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Old Feb 26th 2018, 09:20 AM   #3
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Originally Posted by LlamaMama View Post
I'm not an actual physicist right now, and I have no idea about anything relating to general relativity, but I saw some kind of paper on the internet somewhere titled "Calculations on space-time curvature within the Earth and Sun", and while I didn't understand any of the math behind it, it seemed to basically be saying that something about how general relativity works makes it so that the diameter of the Earth and the Sun, and I would assume all things with mass, is greater if you measured it from the outside than if you did it by measuring its circumference due to some kind of space curvature thing.
That's news to me. Please show me where you read it.

Originally Posted by LlamaMama View Post
know that I probably sound stupid, ...
On the contrary. You don't sound stupid, you sound inquisitive, a good property to have for a physicist.

Originally Posted by LlamaMama View Post
I know this is probably the worst place to ask, and I'm just going to be bombarded with people telling me that this forum is no place for a normal human who doesn't already have a PhD, ..
If anybody ever treats you that way then my advice is to stay as far away from them as possible. This is a help forum. Someone with a PhD doesn't often need help. This forum is for people who want help.

Stick around. I'm sure you'll enjoy it.
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Old Apr 24th 2018, 12:56 PM   #4
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Are you sure you didn't hear about "bigger on the inside than on the outside" on "Dr. Who"?
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Old Apr 24th 2018, 01:35 PM   #5
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Originally Posted by HallsofIvy View Post
Are you sure you didn't hear about "bigger on the inside than on the outside" on "Dr. Who"?
I particularly enjoyed the episode with the painting.

-Dan
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Old Apr 24th 2018, 03:17 PM   #6
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Would I be right in calculating that Eddington's value for the grazing deflection of light past the Sun of 1.6 seconds of arc implies a value of around 9.6 x 1017 metres for the curvature of spacetime in the vicinity of the Sun?
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Old Apr 24th 2018, 04:25 PM   #7
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Originally Posted by studiot View Post
Would I be right in calculating that Eddington's value for the grazing deflection of light past the Sun of 1.6 seconds of arc implies a value of around 9.6 x 1017 metres for the curvature of spacetime in the vicinity of the Sun?
Interesting question. I know that the curvature of the Schwarszchild metric is 0, so we aren't really talking about the curvature (as an inner property of the metric anyway) but I don't know how to relate the starlight deviation to a "curvature" of sorts. Clearly the deviation is smaller the further from the Sun so it isn't even a constant.

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Old Apr 25th 2018, 01:16 AM   #8
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Gravitational space-time curvature is one of those things that is so outside "normal" experience that it is difficult to get ones head around it.

I have not come across the subject of this thread, but it does not sound totally ridiculous (compared with some of the other wild things that physics throws at us).

This would be a tiny, theoretical, effect for all but the largest gravitational fields,
(black holes, neutron stars, and similar bizarre objects).

Another issue with this sort of idea is that while it may appear from the maths,
how do you measure it in practice?
The length of your "measuring stick" will also be changed by the space-time curvature,
so subjectively it all looks the same.
It is difficult to find a way to step outside the problem and have an overview that can observe the phenomena.
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Old Apr 25th 2018, 03:21 AM   #9
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Since a couple of members found this interesting here is my calculation.
I agree with Woody that it is difficult to get a handle on how it works in practice and this was my way of attempting this feat, as I am not an astronomer.

Note that GR is not directly involved as this is a real universe measurement.

In the diagram the dashed ray A from a distant star hidden behind the sun should be invisible on Earth.

The continuous ray B grazes the the Sun's circumference at C in its path and is deflected towards the centre of the Sun.

I have assumed all the deflection occurs at C and that the curvature of deep space between the star and the Sun, and between the the Sun and Earth approaches zero.

Thus the deflection angle, alpha can be calculated from the triangle as shown, given the known distance from the Earth to the Sun, L.
In fact Eddington measured the deflection angle with two teams at two different sites and came up with an average of 1.6 seconds of arc.
I have used this figure to calculate geometrically the radius of curvature that would give this value of deflection.
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Question about "bigger on the inside" space-eddington1.jpg  
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Last edited by studiot; Apr 25th 2018 at 11:59 AM.
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