**(Warning: Major Spoilers Ahead)** You might be here because the science of ‘Interstellar’ got you in a slump, but if you somehow navigated to this article without watching the film… Stop reading now! Bookmark this page, log into Netflix, and go watch it!

Back on topic. In a previous article, we discussed the basic theory and principle behind the 5th dimensional concept. Now, let’s take a look at how it was used to construct one of the biggest plot twists of the film.

It is not 100% accurate to say Cooper arrived at a 5th dimension as he traversed the black hole, but rather he had entered a higher-dimensional world called “the bulk” that contained our localized three-dimensional universe, as well as any additional dimensions imperceptible by human standards.

With that being said, what exactly is “the bulk”, and why can Cooper communicate through it?

**How did Cooper arrive at “the bulk”?**

Time for a little backstory.

After stopping Mann, the Endurance was, unfortunately, slipping towards Gargantua (the black hole) due to its massive gravitational pull. As the limited amount of fuel and life support was becoming a problem, a trip back to Earth was simply not feasible. Alas, with his experience as a NASA trained test pilot and background in Engineering, Cooper planned to take advantage of the situation and use the gravitational pull of Gargantua to slingshot the Endurance to Dr. Wolf Edmund’s planet.

Although, in order to escape Gargantua’s gravity, they must boost, then shed the weight of both the Lander 1 and Ranger 2 spacecraft as they reach maximum velocity and approach the exit point. Why did this have to happen? Well, like TARS would explain Newton’s Third Law – “The only way humans have ever figured out of getting somewhere is to leave something behind.”

Unfortunately, this plan required a pilot for each spacecraft. As such, Cooper weighed the options and withheld this information from Amelia. In the end, the robot CASE was left with Amelia to pilot the Endurance to Edmund’s planet.

After dropping into Gargantua, Cooper and TARS arrived at a location which TARS later referred to as the “Tesseract”. Within this hyper-dimension, Cooper communicated not only the coordinates of NASA to his past self, but more importantly coded the quantum data needed to solve the gravity equation on the second hand of the watch for Murphy.

### How was this possible?

It was explained in the film these “bulk beings” constructed a three-dimensional space within their five-dimensional reality to help Cooper understand what is happening. Time is represented within this higher dimensional world as a physical dimension, which to Cooper is represented by every moment that has occurred within little Murphy’s room. To communicate with these physical representations of time, a force – **gravity**, had to be exerted across spacetime to cause a disturbance in the localized three-dimensional universe.

To find the correct moments in time and communicate, the film used **love**, to which Cooper identified the connection as quantifiable. It does sound a little absurd, but who knows, I can only tell you after falling into a black hole.

**Who are the bulk beings?**

The mention of Bulk Beings in the film can only bring to thought the “Braneworld” theory in particle physics relating to the various string theories. This “Braneworld”, aside from the four that we see, could contain new dimensions beyond our current understanding.

Under the assumption that all versions of string theories can only be “naturally and consistently formulated in a space-time of more than four dimensions” (1), these extra dimensions have to be so compact that it would remain hidden from human experiments. Such assumptions eventually led to questions of “how large these extra dimensions could be without getting into conflict with observations?” (1) As well as “where and how these dimensions could manifest themselves?” (1)

Well, to allow dimensions as large as millimeters to exist, yet remain hidden from human eyes – matter has to be “**localized to a hypersurface (the brane) embedded in a higher dimensional world (the bulk).**” (1)

What does that exactly mean? Let’s take a sandwich for example – the two pieces of bread are the “branes”, while “the bulk” refers to whatever is in between these hypersurfaces. As our universe is embedded in one of these pieces of bread, it is therefore not possible for us to detect additional dimensions that exist within the bulk.

As our localized three-dimensional universe is restricted to a “brane”, the bulk beings in the film could be an alien civilization from another dimension, or maybe even humanity from the future that has learned to harness the ability to traverse “the bulk”.

**Why was gravity used to communicate?**

During the film, Cooper consistently exerted **gravity** across spacetime to communicate with his past self and Murphy at different points in time. But why was gravity used instead of another force that is comparably stronger?

I’m not sure if you have noticed, but** gravity is actually devastatingly weak in relation to the other fundamental forces. **The pull of a magnet (electromagnetism) on a paper clip can easily overcome the** **gravitational pull of the Earth.

This apparent weakness of gravity can be explained, **theoretically** by a constraint of the brane on the localized fundamental forces of nature (e.g., electromagnetism, strong and weak nuclear force), as opposed to **the freedom gravity has to propagate throughout the bulk**. As such, the ability for gravity to traverse the bulk makes it the perfect, and the only candidate for Cooper and Murphy to communicate between the brane and the bulk.

**What is the “Tesseract”?**

We might know the Tesseract as the cube containing the Space Stone, but in the field of geometry, the Tesseract is actually known as the **four-dimensional analog of the cube**. You can imagine it like this – the relationship between a square and a cube, is the relationship between a cube and its tesseract counterpart.

On a technicality, Cooper and TARS were not in the 5th dimension, but rather a three-dimensional space within a five, or maybe even an infinite-dimensional reality. But for simplicity’s sake, let’s called it the fifth dimension.

With this knowledge, we know the geometric shape was not created based on the five-dimensional reality (a penteract), but rather a tesseract, as this three-dimensional space also contained the fourth dimension of time in its physical form. Which portrayed in the film was infinitely complex, and represented every moment of little Murphy’s bedroom.

Based on this current reality, the bulk beings granted Cooper access to infinite time and space so he could communicate with Murphy, and ultimately save humanity.

**References**

- P’erez-Lorenzana, A. (n.d.). An Introduction to the Brane World. Retrieved December 13, 2020, from https://arxiv.org/pdf/hep-ph/0406279.pdf