# Is the Universe a 3D Cut of a 4D object?

• B
• Reapphil
In summary, the conversation discusses the concept of an entity living in 2D space not being able to directly observe a 3D sphere, and how a 4D sphere would appear to us as a 3D sphere. The topic of spacetime being a 4D sphere is also brought up, and the possibility of the expansion of space being a geometrical property of this traversal is mentioned. The conversation then moves on to discussing whether the universe is a 3D cut of a 4D object, with some users mentioning string theory and the holographic principle. However, it is concluded that these theories are interesting but not necessarily helpful in determining the actual workings of the universe.
Reapphil
I have just simple Knowledge, but recently a question came To my mind.
An Entity Living in 2d Space cannot Directly Observe a sphere, but rather a Circle Changing its Size when a sphere is traversing trough the observable 2d plane.
Similar, a 4d sphere would Appear To us as 3d sphere Changing its Size when traversing trough our observable 3d Space.
What if Spacetime is a 4d sphere that we Observe as 3d Ball, but we are obviously Inside. Wouldnt it be Logical, that the Expansion of Space is just the geometrical property of this traversal?

that topic has been discussed here MANY times. I suggest a forum search.

Sorry, maybe Not able To find it due To Langauge issues - any Tipps or Links? Thank you

Thank you. From the threads i was reading, I am not convinced how things work out here (what again was confirmed by the link you sent). There are some users that neglect many threads in the first place. Science is not "having evidence or references", this is hen egg thinking. Science is discussing potential realities, and elaborating experiments to test hypotheses about such realitites - i know that, because this is how i earn my money.
However, I clearly understand that its neither a funny job or duty to explain things over and over again to new users that have no clue in the first place. But in what you sent me, the topic has not been "discussed". It was just neglected.

Reapphil said:
Thank you. From the threads i was reading, I am not convinced how things work out here (what again was confirmed by the link you sent). There are some users that neglect many threads in the first place. Science is not "having evidence or references", this is hen egg thinking. Science is discussing potential realities, and elaborating experiments to test hypotheses about such realitites - i know that, because this is how i earn my money.
However, I clearly understand that its neither a funny job or duty to explain things over and over again to new users that have no clue in the first place. But in what you sent me, the topic has not been "discussed". It was just neglected.
You misunderstand the raison d'etre of the Physics Forum and possibly have either not read, or not understood, the rules you agreed to when you joined. Science does indeed, as you say, include discussing potential realities, and there are forums where that discussion can be carried on but this is not one of them. PF is for established science, as it states clearly in the rules. If there were evidence of your hypothesis, and there were papers discussing that evidence, then it would be a solid topic for PF. When you can cite such papers, please do. I for one would be very interested in hearing that this hypothesis has an evidentiary basis. Until then, it is just personal speculation and not the kind of established science discussed on PF.

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I like it the way @phinds explained it in another thread.

phinds said:
Thinking outside the box is an admirable activity, BUT ... first you have to learn what's IN the box.

To that, I would add, "PF is the place to learn what is in the box."

phinds
Reapphil said:
Is the universe a 3D cut of a 4D object?
The universe is a 4D object. (No cut is physical)

According to some variations of string theory I have heard (but not have studied myself) the universe is a 25D object. But string theory is just a very beautiful theory that explains everything but for which no experimental evidence are available. No one has make some sort of experiment to verify the existence of strings, neither some sort of device that can sense any of the 5th and higher up to 25th dimension.

There is established work that the universe is 2D similar to a hologram. Here is a discussion on the subject with some noteworthy participants. You may find some interesting new insights to help you with your investigations.

richrf said:
There is established work that the universe is 2D similar to a hologram.
The fact that one can create a mathematical construct showing that the information in a 3D sphere can be contained in an area that is the surface area of the sphere is irrelevant to the actual workings of the universe. That is what is indicated by your use of the necessary phrase "similar to", so it's an interesting mathematical curiosity but is, I believe, NOT actually helpful in determining whether the universe is a "cut" of a higher dimension (it's not but the Holographic Principle isn't going to help prove that one way or the other).

## 1. What is a 4D object?

A 4D object is a theoretical concept in physics and mathematics that describes an object with four dimensions: length, width, height, and time.

## 2. How can the universe be a 3D cut of a 4D object?

This idea is based on the theory of hyperspace, where our 3D universe is a projection of a higher dimensional space. Just like a 2D cross-section of a 3D object can appear as a 2D shape, our 3D universe could appear as a 3D shape in a higher dimensional space.

## 3. Is there any evidence to support this theory?

Currently, there is no direct evidence to support this theory. However, some physicists believe that studying the properties of gravity and dark matter could provide clues about the nature of our universe in higher dimensions.

## 4. How does this theory relate to string theory?

String theory is a popular theory in physics that attempts to reconcile the two major theories of physics: general relativity and quantum mechanics. In some versions of string theory, a higher dimensional space is necessary for the theory to work, which could align with the idea of our universe being a 3D cut of a 4D object.

## 5. What implications would this theory have on our understanding of the universe?

If this theory is proven to be true, it could revolutionize our understanding of the universe and how it operates. It would also have implications for the nature of time and the possibility of parallel universes existing in higher dimensions.

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