What I understand is that, according to the string theory our universe is a membrane parallel to several other membranes or (universes). These parallel universes are separated by the bulk or extra dimensions where gravity only can propagate as open strings.

Now what should be the size of that bulk, or how can we see or probe from our 4-dimensional world?

This question is related to this thread:

Constraints on non-compactified extra dimensions

Any help is appreciated!


1 Answer 1


If gravity is the only force that propagates through the bulk dimensions then any observational “probe” must involve gravity. This Wikipedia page describes theoretical empirical tests for large extra dimensions. Some involve the detection of the hypothetical graviton, which is believed to be far beyond our current capabilities.

  • $\begingroup$ Hi, I mean what is the size of that bulk can be? Can it be of order meters ? If so should it be observed or seen in our universe? In other words, if a model assumed and predicted an extra dimension at say $10^5$ meters , will this be logic, or unrealizable prediction ? $\endgroup$
    – Dr. phy
    Oct 24, 2021 at 11:21

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