Extra Dimensions

One of the most apparently obvious properties of the world we live in is that it has three spatial dimensions (obvious to you because you can move left or right, walk forward or backward, or jump up and down).   But one of the most fascinating non-obvious properties that the world might exhibit is that it may have additional (“extra”) dimensions of space that you and I are unable to perceive, either directly through our senses, or indirectly through the many machines that we humans have built, up to the year 2011. This possibility has been considered for at least 90 years, in various forms, and it is alive and well for physicists working at the Large Hadron Collider, and beyond.

This is a very big subject and requires a lot of sub-articles, so I’ll be building this section for quite a while. Of course there are many other articles and books on this subject, including tomes for the public by my famous colleagues Brian Greene and Lisa Randall, but I hope I’ll transcend redundancy here by providing some complementary insights.

Here’s an article (with sub-articles that give examples) on how to think about extra dimensions. We may as well get that straight before trying to describe how extra dimensions might show up at the Large Hadron Collider!

Next, an article (with sub-articles that explain more details) describing some of the signs of extra dimensions that we might look for in experiments.

9 responses to “Extra Dimensions

  1. “Most apparently obvious properties”…

    I don’t think processes in the world are subject to the ihuman idea of dimensions.They happen as they happen. Whether we look at processes from a three or four or ? dimensional view, the results are the same. Length, height and width are independent.

    The diredtions of time are the same as the directions in space. As soon as there is even the slightest fluctuation (= energy = mass) somewhere, time starts in all directions and there is space, expanding with the speed of time., Time within time, space within space etc . Time, energy, mass and space are considered by me as relevant “dimensions”. They are not independent.

    • No, I am afraid this is both conceptually and technically incorrect.

      You say: the dimensions of time are the same as the dimensions of space. This is false. There are crucial minus signs that appear in the equations that assure that you cannot get confused about whether a dimension is a time dimension or a space dimension. Moreover, there is a notion of past and future in time; there is no such notion in space. A physics experiment involves setting up a situation in the past, letting things happen over time, and measuring the result in the future; there is no such notion in space. Causality is all about time; A can cause B only if the distance between A and B in time (divided by the speed of light) is greater than the distance between A and B in space, and if A lies in the past of B (which makes sense if the distances are as I just described.) If you don’t keep track of these differences, you will find modern physics (for instance, black holes) very difficult to understand.

      Second: energy and mass are not spatial dimensions, nor are they time dimensions; they are formally dimensions, yes, but you must not put them in the same category as space and time. If two objects are found at the same time and at the same point in space, they can affect one another, no matter how much energy and mass they have; but if two objects have the same energy and/ mass, they cannot affect one another unless they are close together in space and in time.

      To say this more elegantly: physical laws are local in space and in time, but they are not local in energy or mass. That is a huge and crucial difference between space dimensions and other dimensions like energy. See http://profmattstrassler.com/articles-and-posts/some-speculative-theoretical-ideas-for-the-lhc/extra-dimensions/extra-dimensions-how-to-think-about-them/dimensions-of-physical-space/

  2. IThank you.

    “No, I am afraid ……incorrect.”

    If this is your answer to my “I don’t think ………. independent.”, I don’t understand it. Are dimensions like length, width and height not independent.? Are events caused or affecred by such dimensions?

    “You say ….” etc.

    I need more time to think about that. For the time being I like to mention that any event originating in a particular point at a particular moment will unfold histories from that point and that moment on into each and every direction, thereby creating space.. So I don’t see the problem you mention with regard to the notion of past (and future in space.

  3. As example I take a cube. If one of the three dimensions of the cube changes, the other two have to change as well, otherwise the cube is not a cube anymore. This means that the dimensions of the cube are not independent. If one dimension changes the inescapable changes of the other two dimensions are fully predictable One could say that a cube is an intelligent design. Space however is not. The directions in space are the same as the directions of time.Energy and mass do affect time and space: the curvature of space-time, an acumulation of events..

  4. “If one of the three dimensions of the cube changes, the other two have to change as well, otherwise the cube is not a cube anymore”
    Marten: are you confusing ‘dimension’ with ‘length’ ? Should your statement read: If the length of 1 of the 3 sides of the cube changes, the other 2 have to change as well, otherwise the cube is not a cube anymore. This is a true statement but it involves simple geometry & proportions of a cube and not dimensions.
    I also do not agree that time, energy and mass are ‘dimensions’. We are talking about spatial dimensions as in left/right, forward/backward & up/down….. (x, y & z coordinates for the 3 dimensions).

  5. @ Joe Chan

    Back from a lot of work in France, here is my answer.

    Dimensions like length, width and height shape, are decisive factors for, spatial objects like cubes. They are not endogenous however. They don’t “work together” out of their own.

    What are the dimensions that shape the world? Directions like up/down, back/forward, left/right? Are thery relevant in space? If I go due “east”, the “South Pole is at my right. If I go due “west”, the “South Pole is at my left.You don’t find x, y and z in space. You find them in geometry books.

    So, talking about spatial dimensions, the point in question as far as I am concerned is what dimensions/properties of the world/decisive factors shape the world endogenously, being generic and not independent, their proportions being fully interrelated., continuously changing each other’s proprtions.

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