The 4th Dimension, Spacetime and The Sad Life Of A Photon
Space-time
Special relativity has had implications for both time (time dilation and simultaneity) and for space (length contraction). Its hinted that space and time are somehow connected with the way we saw length contraction work. We therefore shouldn't think of reality as consisting of space and time but rather as one interconnected thing. Space-time.The 4 Dimensions
A 0D object is a point. It purely indicates a location in a system. If we pick two points randomly, the only way to connect them is by drawing a line between them. We are left with a 1D line.If you think of a two parallel 1D lines. The only way to join them is to create a new line perpendicular to the original lines. This new line adds another dimension to the picture. If you think of the 1D lines as 2 parallel x axis, the new line is the y axis adding 2nd dimension.
You can do this with parallel 2D planes. If you have 2 pieces of paper pieces of paper parallel to each other, moving along the existing x and y axes cannot connect them. The only way to connect them is by drawing a line through the 3rd dimension.
So now lets think of a 2 3D spaces. You waking up yesterday and you waking up today. What line can we draw connecting these two spaces? The way to connect these two 3D spaces is with time. Time is the 4th dimension connecting all 3D spaces.
The Flip Book Analogy
The way to think about the reality is as a flip book. Each page represents the universe at a point in time. The first page has the start of the universe and the last page with the end. Our lives is us flipping through each page as time passes. At everyday speeds we all flip through at a constant rate and see the same pages. The thing we see with special relativity is that we don't all have identical flip books. Depending on where observers are in the universe and the speeds they move at, flip books can change. One observer may have a flip book where them reading this blog post and a supernova exploding occur on the same page. Another may have one where the supernova exploded on the same page as when WWII ended. Another will have a flip book that moves pages much slower than all the other flip books (time dilation).
Reality - A Loaf Of Bread
Another way to think about this is as a piece of bread. Reality is a loaf of bread containing all events that have and will occur. We slice the loaf giving each moment in time. The interesting thing is different observers can slice the loaf at different angles meaning their experience of simultaneity differs from ours. We slice the bread at an angle where the launch of the Parker Probe and this blog post release happened on the same slice. Another observer may slice at an angle where they happened 10 slices apart. This is shown in the diagram below.
v is the observers velocity
The white line is what they consider now. It is their now slice of bread or their current page on the flip book.
Changing v means the angle they slice their bread at changes or the contents of pages on a flip book become mixed up.
Moving Through Space-time
Another thing to consider is that we are not stationary in this 4D space time. We are constantly moving through time even when stationary in space. But we can change the rate at which we move through time by moving at faster speeds. It is as if our movement through space-time is split into two components. Being stationary in space means total movement in time. As we move through space faster, more of our motion gets directed into motion through space and less through time. If we move at the speed of light through space, we have no movement through time. The cosmic speed limit is the speed of light and we always move through space-time at this speed; we mainly see movement through time due to our low everyday speeds through space. This also explains why time dilation occurs. Movement through time must slow to ensure total movement through space-time is not faster than light.A way to think of this is as a unit vector where the magnitude never changes. This is just like our speed through space-time never changing. Time is the j component and space is the i component. If we begin to move through space, in order to keep the magnitude of the vector 1, movement through time decreases.
The Life Of A Photon
The extreme case of light itself is even more interesting. Light moves through space at the speed of light meaning. This implies photons have no movement through time to keep to the cosmic speed limit. This agrees with the time dilation formula telling us that photons do not experience time. If we read the flip book of a photon we would only have one page. This page would show everywhere the photon had been in its life. A photon experiences no time so its birth and death all happen instantaneously at one point in time from its perspective.
Summary
Reality/space-time is the collection of all events.Observers do not agree on the order of events or on the location of events but all ultimately have the same events in their collection.
Stationary observers move through their collection of events purely through time at the speed of light.
If observers begin to move, they still move through their collection of events at the speed of light as their movement through time is diverted to motion through space.
We all agree on the order and location of events because as humans our relative velocities are low and so these effects are negligible.
A thought to consider.
Does this imply the universe is a deterministic system?There are observers which consider 10,000 years into the future on Earth as the present.
If the future has already happened for some observers then does that mean what will happen tomorrow is already determined?
We are just moving through space-time through already determined events?
Thanks for reading. If you enjoyed this post or any of my others, follow and subscribe to my blog. Feel free to discuss anything related to this post or ask questions in the comments below.
Check out my other posts on special relativity! (Link to all the posts)
How To Travel To The Future
How Galilean Relativity And The Lorenz Maxwell Equations (The 2 Postulates) Contradict
The Postulates Of Special Relativity
Did you see my previous post? Click the link below to check it out
Length Contraction
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Where Does The Quadratic Formula Come From?
Great Post!
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