The concept of the fourth dimension can be a bit abstract, but I'll try to explain it as clearly as possible. In physics and mathematics, the fourth dimension is often used to refer to a dimension beyond the three spatial dimensions (length, width, and height) that we are familiar with.
In our everyday experience, we perceive the world in three dimensions, where objects have length, width, and height. The addition of a fourth dimension is a mathematical concept that allows for additional degrees of freedom beyond these three dimensions. It is often denoted as time, leading to the concept of spacetime in physics.
Now, if we were somehow able to see or perceive the fourth dimension, it's important to note that our ability to comprehend it is limited by our three-dimensional perception. Imagining or visualizing higher dimensions can be challenging, as our brains are not naturally wired to process them directly. We can, however, use mathematical models and analogies to gain some understanding.
Regarding how the fourth dimension would affect our perception of the universe from an "outside" perspective, that's a difficult question to answer definitively. Since we are bound to our three-dimensional existence, it's hard to conceptualize what observing a higher-dimensional universe would entail. Some theories, such as string theory, suggest the existence of additional spatial dimensions beyond the fourth, but their properties and implications are still subjects of active research and speculation.
As for how the existence of higher dimensions would affect what we can do in our world, it's a topic that often falls into the realm of science fiction. Speculations about time travel, for instance, often involve concepts of manipulating the fourth dimension (time) to travel backward or forward in time. However, the scientific feasibility of time travel is still a topic of debate and far from being conclusively resolved.
In summary, the fourth dimension is a mathematical concept that extends our understanding of spatial dimensions. Visualizing it or perceiving it directly is challenging for us, as we are naturally limited to three-dimensional perception. Speculations about the properties and implications of higher dimensions, including their effects on time travel or other phenomena, often go beyond our current scientific understanding.