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The First Speaker · Boot Joined: 18 May 2005 Posts: 55 Location: UK

I've just finished a module on General Relativity, so I should probably be able to answer your question. Are we trying to decide if a 4D object could distort 3D space-time?

**Posted:** Mon May 23, 2005 6:45 pm

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thebruce

interesting... re:gravity... I think if we apply physics that we know in our 3D world to a 4D world, the physics won't apply... I don't necessarily think a 4D object won't have any gravity - I think the concept of gravity won't apply to a 4D object in our 3D world... we just can't conceive of a 4D object, given our physics rely on 3D objects existing in theoretical 4 dimensions... so the 4D object would likely have similar effects - existing in 4 dimensions, with an effect in the 5th...

I don't think we'd even see a 2D object in a 3D world... the idea of paper-thin still requires a 3rd dimension. In order for us to see something, it must exist with some depth... a 2D object in a 3D world I don't believe would be visible in any way as long as our sight is defined within 3 dimensions... the 2D object may exist, but it would be invisible from any angle... our vision would need to be the same as the being in 2 dimensions - our eyes would need to exist in that 2D plane, and they would only be able to see along the plane...

**Posted:** Mon May 23, 2005 6:47 pm

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hamatoyoshi · Veteran Joined: 02 Aug 2004 Posts: 127

**Posted:** Mon May 23, 2005 6:50 pm

JebJoya · Unfettered Joined: 13 Apr 2005 Posts: 679 Location: UK

Worryingly, I've done a course on Relativity (Special and General) and I'm still a bit confused on how to visualise this one! Essentially, as I remember, gravity is caused by the deformation of Space-Time in the 4th dimension by an object (eg the Earth). Now, if we were to imagine a 4 dimensional object being cross sectioned through our 3 dimensional space, presumably the laws of gravity would not hold, as the object will not be affected by any form of gravity in the 4th dimension? (This is assuming that there is no distortion of the 5th dimension by the 4 dimensional object, but can we leave that aside?)

I don't know, it's rather off topic, but an interesting thought to get your head around...

Jeb

EDIT: ahh, mass + energy... This will require more thought...

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HitsHerMark

Can't you also discover the mass of an object by displacement? No wait... That's volume.

Never mind.

**Posted:** Mon May 23, 2005 6:57 pm

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The First Speaker · Boot Joined: 18 May 2005 Posts: 55 Location: UK

I feel exactly as you do jeb. 3 years at Uni and still stumped by a seemingly innocent question.

Surely, at a bare minimum though, the 3D projection of the object would create its own distortion in our 4D space-time? The extra effects though would probably be impossible for us to determine....an undeterminable mass!!! The cube!!

**Posted:** Mon May 23, 2005 6:59 pm

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JebJoya · Unfettered Joined: 13 Apr 2005 Posts: 679 Location: UK

That'll do, let's leave it at that!

Jeb

**Posted:** Mon May 23, 2005 7:01 pm

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The First Speaker · Boot Joined: 18 May 2005 Posts: 55 Location: UK

lol

Nice project to work on now exams are over though Smile

**Posted:** Mon May 23, 2005 7:05 pm

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JebJoya · Unfettered Joined: 13 Apr 2005 Posts: 679 Location: UK

Exams over? Pah, mine start Wednesday, 11 exams over 2 weeks, fun fun fun...

Jeb

**Posted:** Mon May 23, 2005 7:06 pm

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hamatoyoshi · Veteran Joined: 02 Aug 2004 Posts: 127

**Posted:** Mon May 23, 2005 7:09 pm

Leeravitz

Oh, its at these post -Einsteinian times that I simply wish to retreat into the nearest copy of 'Flatland'...

**Posted:** Mon May 23, 2005 7:10 pm

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**Posted:** Mon May 23, 2005 7:18 pm

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invfish · Veteran Joined: 09 Oct 2003 Posts: 144 Location: Sydney

This is my idea on other dimensions =D

if we look at the 2nd dimension everything is x, y co-ords (length and height). Its mass is always 0. The 2nd dimension could be known as 'thought'.

The third dimension is x,y,z co-ords (length, height and width). Also its mass is greater than or equal to zero (equal if the co-ords are 0,0,0 but then they are the same co-ord which is then a little tricky).

The 4th Dimesion could include time and it could refer to x,y,z over a specific time period. So if the object moves slight to the left in 2 seconds the whole of it within that time frame would be the forth dimension.

I heard the 5th dimension is similar to the 3rd except what you do is you imagine a cube around you and you then turn the cube inside out.

The 6th could be the same as this except over a particular time frame.

Then you have things such as matter displacement and warping etc.. or seeing everything as one energy and change being the only constant. Then you have quantum mechanics where time doesn't seem to apply to the rules of time as we know it. Then you have different energys and so forth. It goes on and on and on.. well as far as the imagination can stretch Wink

..and then stretch your heart just as big =)

**Posted:** Mon May 23, 2005 7:51 pm

Violet · Decorated Joined: 08 Mar 2005 Posts: 217

**Posted:** Tue May 24, 2005 8:30 am

tangohead

**Posted:** Tue May 24, 2005 10:06 am