Why Time is considered a 4 th dimension ? Why Gravity cannot be considered as a dimension ? What is a 5th dimension ?
In: Physics
Because two objects can be at the same place at different times without colliding.
Two objects cannot be at the same place same time, but different gravity.
If there is a 5th dimension, then an object would be able to be at the same place same time, but different 5th dimension, without colliding.
Because objects move through dimensions. You can move up/down, left/right, or forward/backward. Since we are all always moving through time as well it is considered a “4th” dimension. Not to get too much into it but gravity is one of the 4 known forces that interacts with objects in the universe and not a dimension. Five dimensions are only possible in mathematics as far as I know.
Think of each dimension like a part of a set of coordinates. To find an object’s location on the surface of the Earth you’d need to know its location in the physical dimensions (on the surface of the Earth those would be latitude longitude and altitude), but those would be useless if the object is moving. In that case you’d also need to know the time when it will be at that physical location.
If you could view an object in the 4th dimension it would look like one large object that is a combination of all the physical locations that object has ever been in starting from the beginning of its existence to when it is destroyed. Pick any point along its lifetime and it’ll be on a line, with the past going one way and the future going the other. This is just like the other dimensions except the object’s traversal of the 4th dimension can only go in one direction, and at a fairly constant velocity.
Gravity is one of the essential forces in the universe.
A dimension is an axis that describes the position of an object. You may think we live in a 3-dimensional universe, but according to String theory, it has 10 dimensions but we only perceive a few. For now let’s only focus in 4 dimensions, X,Y,Z and Time.
Let’s put it this way. You could describe the position of a chair in a square room with 3 axis, X,Y and Z. Let’s call X the wall to the South, Y the wall to the West and Z the ground. If the chair was 1 meter tall and it was 2 meters away the South wall, 3 meters away the West wall, it’s coordenates would be (X=2, Y=3, Z=1). Right now it’s 17:30 and the chair is at the position (2,3,1). If I come 5 minutes later and move the chair 1 meter away from the south wall, it’s new coordenates would be (3,3,1) at 17:35.
But what if the chair was constantly and randonly moving? Every second that passes, the coordenates would change. How do we measure them? We could freeze time, check the coordenates for that time and write them down. So by 17:40, the coordenates were [insert random value]. That’s why time is a dimension. It’s required to describe the position of an object. That’s why in some physics or chemistry problems you may find “For T=0, the position of the body was [x,y,z]”.
A “dimension” in classical physics is a space through which you can move.
Like space, we appear to move through time in a way we perceive as having points (or coordinates) to it.
Gravity, however, is a property that emerges when a mass interacts with the combined fabrics of space and time called “spacetime”. It somewhat similar to a bowling ball on a trampoline; smaller balls will roll into the “gravity well” created by the bowling ball on the surface of the trampoline.
Higher dimensions (like the 5th dimension) are aspects of mathematical models that attempt to make modern physics more complete.
Relevant video: https://youtu.be/3KC32Vymo0Q
A dimension just means something that has an independent measurement. We say we live in a 3-dimensional world because we cannot make a construction which has more than 3 lines which are all at right angles with each other.
Time can be thought of as a 4th dimension because, just as an object’s location in space can be represented as 3 coordinates (x, y, z), an object’s motion can be represented as 4 coordinates (x, y, z, time).
For most practical purposes, we only have 3 _spatial_ dimensions, but we can keep adding dimensions as long as each dimension is independent of the other dimensions. E.g. a point in 5-D might be an object’s location (x, y, z) at a given time (t) with a given color (c) thus producing a coordinate system of (x, y, z, t, c). I haven’t the faintest idea why that might be useful, but it’s logically* possible.
Edit: *logically = mathematically
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