- #1
Ratzinger
- 291
- 0
Why is according to relativity the flowing of time an illusion (as Einstein put it)?
I believe the quote the OP is referring to is the remark Einstein made in a letter to the family of his long-time friend, Michele Besso on Besso's death. He said that although Besso had died before him, it was of no consequence because: "...for us physicists who believe, the separation between past, present, and future is only an illusion, although a convincing one."pervect said:Sounds like philosophy to me...
Out of curiosity, what was the exact quote of Einstein you had in mind, anyway?
Yes, but the standard idea of the "flowing time" people is that there is a single objective present which is the same for everyone. Once you accept that one's definition of simultaneity depends on an arbitrary choice between equally valid coordinate systems, you've basically accepted the "block time" view.Andrew Mason said:This hardly qualifies as a statement that as a matter of physics, Einstein believed that past, present and future was an illusion. Certainly, in a single inertial frame of reference it is not true and Einstein certainly did not believe that.
"...for us physicists who believe, the separation between past, present, and future is only an illusion, although a convincing one."
The word 'illusion' is a loaded term, it suggests that perspective is less real than the 4D block time one, yet we can only observe and test the nature of time as conscious observers - hence it might well be said that it is the (3+1)D perspective that is 'real' and the 4D block time that is the illusion.Ratzinger said:So to have flowing time consiousness or some cognitive system is needed.
If you look at the physics alone block time is inescapable. But isn't the perspective that does not assume conscious observer more fundamental, more valid?
Is not the conscious view, the flowing time view as Einstein said it only a convincing illusion?
If you want to describe an observer's experience of the universe, you should only talk about how the observer's past light cone changes as their proper time increases along their worldline--after all, the the idea of distant events with spacelike separation being "simultaneous" is just an abstraction based on Einstein's clock synchronization convention, you don't actually experience these "simultaneous" events until later when light from them has had time to reach you. I think it is fair to say that relativity makes the notion of any sort of "universal now" problematic, although you are free to imagine that each observer has their own separate "now" which is moving forward along their worldline, or even take the solipsistic position that it is only your now that is real and everything outside of your past light cone is undetermined. But a question like "what is my friend on Mars doing right now" cannot have any sort of single objective answer unless you introduce something like the "metaphysically preferred reference frame" idea I talked about in my last post.Garth said:IMHO the question of whether the 'block time universe' exists or not is a matter of perspective.
SR has taught us to look at the world as a 4D continuum, with proper time [itex]\tau[/itex] replacing t, and 4D geometric objects, such as 4-momentum, replacing their classical equivalents.
However we are creatures of a conscious (3+1)D world, and as observers on a particular world-line through that 4D continuum, we define our own foliation of space-time into a particular 3D space + time. The only world that is 'real' to our consciousness is that particular foliation with its sensation of the passing of time.
Which perspective do you therefore use to describe the universe? 4D block space-time, or (3+1)D space and time? It depends on what is appropiate to the task in hand. Both are equally valid descriptions, however each is not necessarily the most appropiate description for a particular use.
To do physics from a geometric perspective choose 4D, to describe a particular observer's experience of the universe (e.g. our own perspective) choose (3+1)D.
Garth
I'm glad we agree.JesseM said:If you want to describe an observer's experience of the universe, you should only talk about how the observer's past light cone changes as their proper time increases along their worldline--after all, the the idea of distant events with spacelike separation being "simultaneous" is just an abstraction based on Einstein's clock synchronization convention, you don't actually experience these "simultaneous" events until later when light from them has had time to reach you. I think it is fair to say that relativity makes the notion of any sort of "universal now" problematic, although you are free to imagine that each observer has their own separate "now" which is moving forward along their worldline, or even take the solipsistic position that it is only your now that is real and everything outside of your past light cone is undetermined. But a question like "what is my friend on Mars doing right now" cannot have any sort of single objective answer unless you introduce something like the "metaphysically preferred reference frame" idea I talked about in my last post.
nothing about relativity that suggests that events outside one's past light cone are necessarily "predestined"
the the idea of distant events with spacelike separation being "simultaneous" is just an abstraction
Only if you accept that there can be no universal truth about which events have already happened and which haven't (assuming you don't use the 'metaphysical preferred reference frame' idea)--either each observer would have his own separate truth, or you could adopt that solipsistic view that only your point of view is the truth.Ratzinger said:That was the next thing I wanted to ask about. Is that safe to say that relativity does not imply predestination?
Because there's no physical reason why you must to associate each observer with a reference frame constructed in the way Einstein does it, that's just a human convention. A given observer could use a different clock synchronization convention than Einstein's for his rest frame (although this would be less elegant because it would mean the equations to represent the laws of physics in different inertial frames would no longer be the same), or he could even define "his" frame as a frame where he was in motion. Also, what about an accelerating observer? If you say that his "now" at each moment is defined by the inertial frame in which he is instantaneously at rest, then it will be possible for events that were in his past at an earlier time according to his clock to be in his future at a later time according to his clock.Ratzinger said:But why is that? Is not everything on my now list, no matter how far away it takes place equally real? If a glass drops in my room now or if that happens on Andromena now, both are unchangeable facts and I can say a second later they happened.
I think that, by definition, time can only flow in one direction, as I shall explain:Ratzinger said:Yes, that’s the quote I was referring to.
And what JesseM and Paul Davies say is what I intended to ask about.
Accepting that there are no preferred nows, i.e. accepting relativity leads automatically to block time, so it’s not a view and no philosophy but inevitable consequence of Einstein’s theory. Or not?
But that is a disturbing consequence, to me far more disturbing than twin paradoxes and shrinking meter sticks.
Ratzinger said:But why is that? Is not everything on my now list, no matter how far away it takes place equally real? If a glass drops in my room now or if that happens on Andromena now, both are unchangeable facts and I can say a second later they happened.
Einstein's theory of relativity states that time is not an absolute concept, but rather a relative one. This means that the passage of time can vary depending on an observer's frame of reference. For example, time can appear to pass slower for someone who is moving at a high speed relative to someone who is stationary.
Einstein's theory of relativity explains that the perception of time is dependent on an observer's position and movement in relation to other objects. This suggests that time is not a fundamental aspect of the universe, but rather a human construct that helps us make sense of the world around us.
While the concept of time as an illusion may seem counterintuitive, it is supported by scientific evidence and has been confirmed through experiments such as the famous Hafele-Keating experiment. However, our perception of time is still a very real experience and is necessary for functioning in everyday life.
Einstein's theory of relativity revolutionized our understanding of the universe and has had significant implications for many areas of science, including physics, astronomy, and cosmology. It has also challenged our traditional understanding of time and space, leading to new theories such as the concept of spacetime.
The idea of time as an illusion is a widely accepted concept in the scientific community, although it is still a topic of ongoing research and debate. Many scientists and philosophers continue to explore the implications of Einstein's theory of relativity and its impact on our understanding of time and the universe.