Dan Roche *** (Daniel Craig Roche)
Dan Roche ***
(Daniel Craig Roche)
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Dmitry Selemir
As a former physicist, I felt I had to jump into this one, since I feel like there is a bit of a misconception.
First of all gravity is not invariant — there is nothing magical about 'g' itself (which is measured in m per second squared, by the way — it is acceleration, not velocity). In fact g varies quite a bit since it depends on mass. the formula for g is G x m/d^2, so gravitational constant times mass of the object (in case of g we are used to — it's mass of the Earth) and divided by the distance. The force (you get the force by multiplying the 'g' by the mass of second object) exists between any object and particle, it's just usually the masses are so small that we don't notice the effect and so it's natural to think that Earth's gravity is the only one we actually experience. There were numerous experiments conducted to measure the gravitational constant. Usually they are done by measuring the interaction between two steel spheres of known mass. It is a very delicate experiment that requires precision. The first one of it's kind was ambitiously called weighing of the Earth, which, in a way, it is — since it indeed allowed us to determine its mass.
As a result, 'g' will be different for different objects and that's why gravity we would experience on Mars or on the Moon is different to the one we experience on Earth.
In fact even on Earth gravity is not the same everywhere. The formula we are used to is only an approximation (good enough in most cases)  - it assumes that all of the mass is concentrated in the centre. This is, of course, not the case. It is also not evenly distributed and there are plenty of 'anomalies' where 'g' force we experience is going to be different. The differences are relatively small, but, of course measurable.
Going back to the original question — can we think about gravity as another dimension? First of all if we were to try and think along those lines we will have to go away from gravity and consider mass instead, since this is a fundamental property, responsible for gravity. We can expand further and ask — can we consider mass, electrical charge and magnetic properties alongside the dimensions and call them dimensions too. It's an interesting proposition — but I think the answer is ultimately no. There is a fundamental difference between them. Dimensions are needed to describe the changes happening with he object, ultimately we breakdown all these changes into components and the four dimensions we are used to are generally sufficient to do that without violations of any known laws of physics. Extra dimensions are required if we go to the level of elementary particles, where things do not quite fit in. The thing about mass/electrical charge etc. (there's a lot more properties like this once we drill to elementary particles) — we can not change them without external interactions — this will violate the energy conservation — the most fundamental of all laws of physics. Essentially that means we can not travel within those 'dimensions', which removes the need for them to be considered as dimensions. Perhaps we will discover something that will change this one day, you never know.
This actually brings me  to another point. From some of the articles and comments, including here on Scriggler — I notice that there is this big misconception about the way scientific approach and scientific thought works. People tend to think that scientists approach it as if they found absolute truth. There is no such thing in science. The proper way to go about it is — science is looking for the most plausible explanation of observed phenomena and each theory is tested through it's consequences, i.e. each theory suggests a set of unique outcomes that can be checked experimentally. For example in our gravity problem — the theory suggests that there should be interaction between small objects, governed by the same laws as interaction between us and the Earth. This is a measurable effect, that proves that the theory was correct. It is not however set in stone — one day we'll discover new facts that will show the weaknesses of this theory or its limitations and it will need to be changed or adjusted. These adjustments however need to be justified by the actual need, i.e. observable phenomenon that can not be described or explained within the existing theory. This is to me a key element of scientific thought — it is always, strike that — ALWAYS evidence based. Only things that are absolutely necessary are considered, which is part of the beauty of the scientific approach, at least to me. Incidentally this is one of the reasons why I consider myself an atheist, since from my (limited I concede) analysis there is no evidence that necessitates any kind of supreme being and if it's not absolutely necessary — there is no need to introduce it.