1. Hi all! I was recently introduced to the idea of 4D space. I've done some research but I'm still having trouble understanding it. So I googled what are the 4 dimensions. I saw many articles saying that we have the 3 spatial dimensions and one time dimension. Another said that there is spacetime dimension. If anyone can please elaborate on that idea for me. From what I understand spacetime and time are basically the same thing. I'm no too sure. How can I imagine a time dimension?

Another said that it is possible for us to have 4 spatial dimensions and that can be represented as a tesseract. Then my next question is how can gravity affect the 4 spatial dimensions and 1 time dimension?  2.

3. I'm not an expert but you need to clarify what you are asking. Mathematically you can have as many spatial directions as you like (some string theories have 10 or 11). In relativity space-time has 3 spatial dimensions and one time dimension. Are you interested in 4-D space,-time or higher spatial dimensions?  4. It looks like you are asking a physics question. Relativity theory has three space dimensions and one time dimension. Space-time is a way of describing them together as a four dimensional thing. String theory has a bunch of additional space dimensions, but you can safely ignore it for now, since string theory has yet to be tested in the lab.  5. Originally Posted by mathman It looks like you are asking a physics question. Relativity theory has three space dimensions and one time dimension. Space-time is a way of describing them together as a four dimensional thing. String theory has a bunch of additional space dimensions, but you can safely ignore it for now, since string theory has yet to be tested in the lab.
Just musing here.Spacetime can be defined as a mathematical model that is incredibly successful in its predictions (even at the subatomic level I think)

I know some (was it Lorenz?) have said that we can no longer think of space (ie distance) and time separately but only entwined.

Is there wriggle room though since spacetime is still just a model.

Time can also be measured ,it seems without movement taking place as in radioactive decay etc.

So can we disentangle space and time after all (just not in the spacetime model itself)?

Actually this is probably off topic..  6. Originally Posted by geordief I know some (was it Lorenz?) have said that we can no longer think of space (ie distance) and time separately but only entwined. So can we disentangle space and time after all (just not in the spacetime model itself)?
Here's how I envision the 4th dimension spacetime -- although I'm the first to admit the concept is way beyond my puny brainpower.

You know that light moves at the speed of light, C, 186,000 mi/s right? And you know how as one APPROACHES the speed of light, time slows down? In effect that means that photons exist everywhere along their path of travel simultaneously. From a photon's point of view, leaving a distant star and arriving at your retina are simultaneous events.

Therefore, time -- in effect -- moves at the speed of light. If you could travel in any direction at the speed of light you would, from your viewpoint, arrive at your destination instantaneously. Everything around you would progress in normal time, at the rate of 1 second per second (unless traveling at a significant percentage of C) but from your viewpoint, traveling at C, there would be no time passage at all.

THAT is the 4th dimension. That is what "spacetime" is. At the speed of light, there is no distance between two points in space, there is no passage of time. You just exist everywhere simultaneously -- a 1-dimensional line -- along the path of your travel from Point A to Point B.  7. Originally Posted by NoCoPilot  Originally Posted by geordief I know some (was it Lorenz?) have said that we can no longer think of space (ie distance) and time separately but only entwined. So can we disentangle space and time after all (just not in the spacetime model itself)?
Here's how I envision the 4th dimension spacetime -- although I'm the first to admit the concept is way beyond my puny brainpower.

You know that light moves at the speed of light, C, 186,000 mi/s right? And you know how as one APPROACHES the speed of light, time slows down? In effect that means that photons exist everywhere along their path of travel simultaneously. From a photon's point of view, leaving a distant star and arriving at your retina are simultaneous events.

Therefore, time -- in effect -- moves at the speed of light. If you could travel in any direction at the speed of light you would, from your viewpoint, arrive at your destination instantaneously. Everything around you would progress in normal time, at the rate of 1 second per second (unless traveling at a significant percentage of C) but from your viewpoint, traveling at C, there would be no time passage at all.

THAT is the 4th dimension. That is what "spacetime" is. At the speed of light, there is no distance between two points in space, there is no passage of time. You just exist everywhere simultaneously -- a 1-dimensional line -- along the path of your travel from Point A to Point B.
I couldn't really answer you as I don't have the education apart from what I may have learned on forums like this.

Even so ,I doubt the spacetime is ever referred to as the 4th dimension.(never come across that certainly).As well as I know spacetime is a mathematical model and not a physical thing as such. (not any kind of a dimension either)  8. Originally Posted by GryphonWest Then my next question is how can gravity affect the 4 spatial dimensions and 1 time dimension?
Einstein unified 3 dimensional space and also time in his theory of special relativity.
Gravity was later incorporated into general relativity, and it answers the question why the earth is suspended in space. It's also moving at about 1.5 million miles a day in its orbit, following as straight a line as it can it warped space-time.

Time is a variable. It depends where you are and what speed you are travelling. The only constant is the speed of light.
If you are moving toward a light source or away from it you will measure the speed of light the same. You are punching a hole into the fabric of space-time which will slow down time, but only if you travel at near light speed would you notice a big difference.
The closer you are to the pull of gravity from a large object like the earth the more time will slow. If you are at the top of a mountain then time will run slightly faster than at sea level.  9. Space-time is considered as a single entity, since going from one inertial system to another (special relativity), time is changed as well as space coordinates.  dimensions, maths, physics, string theory, tesseract 