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"Time is Not the Fourth Dimension"

Orphia Nay

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Orphia Nay
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"The concept of time as a way to measure the duration of events is not only deeply intuitive, it also plays an important role in our mathematical descriptions of physical systems. For instance, we define an object’s speed as its displacement per a given time. But some researchers theorize that this Newtonian idea of time as an absolute quantity that flows on its own, along with the idea that time is the fourth dimension of spacetime, are incorrect. They propose to replace these concepts of time with a view that corresponds more accurately to the physical world: time as a measure of the numerical order of change."


"“Einstein said, ‘Time has no independent existence apart from the order of events by which we measure it,’” Sorli told PhysOrg.com. “Time is exactly the order of events: this is my conclusion.” "

http://www.physorg.com/news/2011-04-scientists-spacetime-dimension.html

Is this really a new idea? I've always thought time being a separate dimension is a rather weak argument.
 
69dodge said:
I read the article, but I can't figure out what it means.
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:) :thumbsup: As far as I can tell, they're saying that calling time another dimension is just making stuff up out of the three dimensions that do exist.

But I could be wrong. ;)
 
It's very hard to be sure based on a news article, but this sounds like nonsense.

'“Minkowski space is not 3D + T, it is 4D,” the scientists write in their most recent paper.'

"Minkowski space" is a specific mathematical term that refers to a spacetime with 3 space dimensions (or in general some other positive integer) and one time dimension. The total spacetime dimension is 3+1=4, but there is an important mathematical (and physical) distinction between space and time in Minkowski space. That's a fact, it's true by definition of Minkowski space.

When Einstein (and Lorentz) discovered relativity, one of the implications was while time and space are different, they are not as disconnected as previously thought - they form a 4D spacetime (namely Minkowski space), and Lorentz transformations can partially rotate space into time. That's what leads to effects like time dilation and length contraction. But that has been understood since 1905, all modern theories of fundamental physics incorporate it, and anyone that's taken more than a year or two of college level physics understands it.
 
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sol invictus said:
When Einstein (and Lorentz) discovered relativity, one of the implications was while time and space are different, they are not as disconnected as previously thought - they form a 4D spacetime (namely Minkowski space), and Lorentz transformations can partially rotate space into time. That's what leads to effects like time dilation and length contraction. But that has been understood since 1905, all modern theories of fundamental physics incorporate it, and anyone that's taken more than a year or two of college level physics understands it.
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From what I understand, Einstein initially didn't like the idea of time being a fourth dimension, and after Special Relativity became well-known he complained to those who drew that conclusion from his theory. However, he apparently warmed up to the idea while working on General Relativity.
 
Anyone who thinks time has no physical reality has never spent 7 hours at Heathrow Terminal Five.
 
The article seems to me to be drivel.

Sol invictus is right.

Still, time as a fourth dimension is a bit of a hack. Representing spacetime using quaternion algebras is a lot prettier, and you don't have to remember weird operators or the right-hand rule.
 
In a one-dimensional universe, time can still exist.
In a two-dimensional universe, time can still exist.
In an n-dimensional universe, time can still exist.
So either time isn't a true dimension, or at best it's an n+1 dimension.
 
Dorian Gray said:
In a one-dimensional universe, time can still exist.
In a two-dimensional universe, time can still exist.
In an n-dimensional universe, time can still exist.
So either time isn't a true dimension, or at best it's an n+1 dimension.
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Can time exist in a one and two dimensional universe independently of an observer who is capable of observing the "lower" dimensions? In other words, do you need an n+1 universe to even say that time can exist in an "n" or an "n - 1" universe?
 
One point to clarify is that it depends on the question being asked.

If the question is about the structure of the universe as per relativity, then it's appropriate to call time 'the fourth dimension' in so far as spacetime is treated as a 4-manifold endowed with a particular type of geometry.

If the question is about more general 4-dimensional objects (say, the 4-sphere) the answer is that time is not the fourth dimension.
 
aggle-rithm said:
From what I understand, Einstein initially didn't like the idea of time being a fourth dimension, and after Special Relativity became well-known he complained to those who drew that conclusion from his theory. However, he apparently warmed up to the idea while working on General Relativity.
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Well, I have no idea what Einstein's thought process was. But the modern point of view is that time is the fourth dimension, but that it is distinct in a mathematically precise way from the three spatial dimensions.

One interesting implication of the differentness of time is that we know perfectly well how to formulate physics in n space dimensions and 1 time (and some such theories with n>3 are even completely consistent with all our experimental data), but we have little or no idea how to make sense of theories with more than one time dimension.
 
I thought space/time was the dimension and one cannot talk about space without considering time as well. So we are constantly moving through time. If we move through space, that's like going diagonally on the time road in that it slows down your forward time progress relative to the speed with which you travel in space. The faster you travel in space, the slower you travel forward in time.

I imagine that's a pretty much lay person's interpretation, but that's the one that works for me at the moment.
 
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Dorian Gray said:
In a one-dimensional universe, time can still exist.
In a two-dimensional universe, time can still exist.
In an n-dimensional universe, time can still exist.
So either time isn't a true dimension, or at best it's an n+1 dimension.
Click to expand...

Confused about how you get to the bolded bit. If you have a 1-dimensional space where time exists, isn't it a logical extension to say you have a 2-dimensional spacetime?
 
One could say exactly the same kind of thing about space. 'Space has no independent existence apart from the relations of events by which we measure it.' Umm... yes, okay? You don't get measurements of space except through some stuff related to some other stuff. Yet it doesn't mean there aren't genuinely three spatial dimensions.
 
Orphia Nay said:
calling time another dimension is just making stuff up out of the three dimensions that do exist.
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I wonder, is it so self-evident that "three dimensions" exist in any other sense than in the human mind? What would they be: width, height, depth at 90 degrees angle to each other? Alternatively you could define a different, larger, set of dimensions at different angles to each other, to cover what we call "three-dimensional" space.
 
JJM 777 said:
I wonder, is it so self-evident that "three dimensions" exist in any other sense than in the human mind? What would they be: width, height, depth at 90 degrees angle to each other? Alternatively you could define a different, larger, set of dimensions at different angles to each other, to cover what we call "three-dimensional" space.
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You need 3 numbers to specify a location in space (plus 1 to specify an event in spacetime), just as you need two (latitude and longitude) to specify a point on the (2D) surface of the earth.

That's the definition of the number of dimensions - it's got nothing to do with the human mind.
 
JJM 777 said:
I wonder, is it so self-evident that "three dimensions" exist in any other sense than in the human mind? What would they be: width, height, depth at 90 degrees angle to each other? Alternatively you could define a different, larger, set of dimensions at different angles to each other, to cover what we call "three-dimensional" space.
Click to expand...
Interesting idea.
 
sol invictus said:
You need 3 numbers to specify a location in space (plus 1 to specify an event in spacetime), just as you need two (latitude and longitude) to specify a point on the (2D) surface of the earth.

That's the definition of the number of dimensions - it's got nothing to do with the human mind.
Click to expand...

That makes sense. So much for JJM's idea, but it was still interesting to contemplate. :)
 
Well for sure time is not geometric 4th dimension. Because by no operation in time you can make left boot from right boot .. in space with 4 geometric dimensions all you need to do is rotate the boot around arbitrary plane.
On the other hand, the convention is useful, mostly in relativity problems .. so what the heck ..
 
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