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## Main Question or Discussion Point

So what exactly is meant by time as a 4th dimension?

I've read in a couple of places a nice visualization of the effect of time dilation using velocity as a 4-component vector. Since the maximum possible velocity is the speed of light, as something travels through space at close to the speed of light, the "time-component" of its velocity must necessarily be smaller.

Does this example have any meaning, or is it simply a useful illustration for the layman?

In modern physics, what are the distinctions between space and time? And is it worth asking the question in the first place?

The most obvious difference to me is that one can travel backwards in space, but not in time; but then it occurs to me that since the universe is constantly expanding, can one really travel "backwards" in 3-dimensional space?

I've also read that some theorists posit that in the first moments after the big bang, space and time were "smeared" together, and that time only emerged as a seperate dimension as the universe grew. What exaclty does this mean, and how does it relate to the first part of my question?

All illuminating answers greatly appreciated!

Cheers,

Anders

I've read in a couple of places a nice visualization of the effect of time dilation using velocity as a 4-component vector. Since the maximum possible velocity is the speed of light, as something travels through space at close to the speed of light, the "time-component" of its velocity must necessarily be smaller.

Does this example have any meaning, or is it simply a useful illustration for the layman?

In modern physics, what are the distinctions between space and time? And is it worth asking the question in the first place?

The most obvious difference to me is that one can travel backwards in space, but not in time; but then it occurs to me that since the universe is constantly expanding, can one really travel "backwards" in 3-dimensional space?

I've also read that some theorists posit that in the first moments after the big bang, space and time were "smeared" together, and that time only emerged as a seperate dimension as the universe grew. What exaclty does this mean, and how does it relate to the first part of my question?

All illuminating answers greatly appreciated!

Cheers,

Anders