I have been inspired to ask the question by this thread. The OP wonders how time travel would actually work and at first my knee-jerk reaction was to reply it wouldn’t. I immediately decided not to reply at all. But my initial disposition seemed to linger and since I had some time ;), I decided to initiate this discussion.
As a teenager, sci-fi was my philosophy. What turned this grandiose perspective on reality into a giant on feet of clay was time travel. I was still very young when I realized it was impossible. I don’t remember my exact thoughts, but today I would say that time travel violates thermodynamics.
Today I would also add that it is likely that time does not even exist at the most fundamental level of physical reality. The Universe is a physical process whose dynamic life only exists now – physically speaking, there is no past or future: only present.
Time is a function of our imperfect perception of reality. Important categories such as motion, causality, or existence cannot be comprehended by the human brain in the absence of time. The emergence of the concept of time may be an evolutionary adaptation of the human mind so that people could make sense of the world the live in and manage to use their intelligence so that they could survive and thrive.
But if there’s no living thing to observe or perceive reality, the universe automatically goes back to its atemporal labor.
Things happened in ordered sequence for billions of years before the first human being. I can see the evidence of this frozen in this rock on my desk. Deep Time is real.
The foundation of the strong anthropic principle is the “center of the universe” fallacy. Each aspect of it is apparent from observation, and each is so because each is an artifact of observation. If the universe required an observer, what possible cause would make recently sentient great apes the causal nexus of reality? In order to be so, the universe had to get along without it’s primal cause for almost the entire current age of the phenomenon. Even allowing for parallel evolution on multiple worlds of sentients, the first few hundred million years still had to exist without an observer, and then suddenly develop an existential need for one at the instant one was extant. Absurd.
Relativity theory posits that space-time is one thing. Time cannot be separated out from the rest any more than a space-like dimension.
What actual physical meaning does your version of time have? What did the laws of physics look like until time suddenly appeared? Could events propagate faster than the speed of light, since time is necessary to give that a speed? How did the universe evolve without time? When the first perceiver perceived time how did it propagate out to the rest of the universe? Did everything in the universe suddenly slow down to accommodate speed? Or did everything in the universe suddenly start aging rapidly in order to give the appearance of past time?
Resorting to terms associated with time, such as “current”, “age”, or “years”, can only show how the human brain makes use of certain concepts to produce logical reasoning. Invoking units of time to prove that time itself is real does not look convincing to me - they’re all abstractions, which causes me to think time itself may be a human abstraction related to the changing nature of reality.
A human mind is not a “blank state” at birth. It has been shown that young babies find it weird that an object should suddenly disappear, or that a large object should fit into a small container. Kant mentions a priori categories that belong to our mind rather than to the universe itself. Rather than describing reality, “causality” and “beforeness” for example show the manner in which the human mind can make sense of the overwhelming host of external stimuli it goes through.
When I suspect that time may not be a physical attribute of the universe, I experience the same feeling I have always had when thinking that numbers do not exist independently from observers. The title of this thread alludes to this well known thought experiment: “if a tree falls in a forest and no one is around to hear it, does it make a sound?” I remember the first big revelation I had when my classmates and I began to study physics in school: colors do not really exist. A greater realization was the fact that there is a dichotomy between what reality is like and and the way the human mind can function. Colors belong to our mind, whereas light frequencies exist in the real world. Vibrations travel in the media surrounding us, but sound can only be found in our hearing system. In the same way, there may only be entropy out there, which the human mind perceives as time.
Do chemical processes happen in the absence of consciousness? MrDibble’s response in the post #2 remains relevant, even if we delve into philosophical/semantic discussions of perception. Long before humans evolved, the processes through which humans could evolve were underway, in stars fusing helium into heavier elements, and those elements coalescing into a planet, and on that planet elements combining into amino acids and proteins and then billions of years later, humans chatting over the internet. Unless you’re suggesting some variant on Last-Thursdayism or that our understanding of cosmology, geology and chemistry are extremely incorrect, what’s your point?
Stating that our description of reality is distinct from reality itself does not mean science is wrong. Science may be regarded as our best reflection of reality, a formalized structure of our perceptions and the ideas that we can generate based on these perceptions.
My point is that the numbers and symbols we use in equations may not stand for real things despite the essential role they play in our effort to understand reality. The Universe may strictly exist in the present, I have already said that, past and future being creations of the human mind.
Your post invokes the processual nature of reality, where one can observe various states of the Universe, all coming one after the other in a sequence that suggest a cause-and-effect flow of events. I don’t deny the validity of this description. I’m just not sure whether it shows how the Universe functions or merely how our mind works - the arguments being that there is already an accepted dichotomy between phenomena and noumena, and certain scientists claim that time may not exist.
This sounds like a dressed-up version of solipsism, truth be told. You can argue it but I can’t see how you could possibly prove it, and if the past is just a creation of the human mind, does this mean the billions of years we have inferred that the universe and the Earth existed before humans evolved are a delusion? An illusion? A miscalculation?
Further, “color” might be simply a matter of perception, but do you acknowledge that energy has a waveform? The waveforms can be of different lengths? That “length” has a meaning, in the sense that if I have an object that is 680 nanometres in length and I give this object to another person, it will still be 680 nanometers in length? Well, if a waveform is that length, some people might perceive it as “red” and other people may perceive it as reddish-orange and some people may not be able to perceive it at all, but that energy wave will exist whether someone is perceiving it or not.
If you’re maintaining that the waveform doesn’t exist if no-one is perceiving it, then I don’t know what to tell you. We can detect energy like this coming from stars that are so far away that the energy was generated long before human existed and is just arriving now.
The op may be trying to channel John Wheeler some:
Personally I think it is complete bunkum but the concept I accept, that space-time is one object with time a dimension of as much as any spatial dimension, is pretty strange to grok too!
No, that is not what I have said. Not only I agree that reality exists independently from the human mind but I also suspect that its attributes may be different in number and nature from the ones we use to describe the Universe. The ever-changing Universe is real. Its different states are also real. The increase in total entropy is also real. What may not be real is time. In the absence of any life form perceiving these things, all there is can be described as an atemporal labor whose processual existence can only be found now, in the present. The analytical nature of the human mind may allow one to isolate t1 and t2 as distinct values of a perceived property named time but the reality of these two different moments may be as illusory as the existence of the two different sides of the Moebius strip.
All there is may actually be the present state of the universe. Embedded in this present state, one can see various degrees of change of the matter and energy that the universe consists of. Discriminating between different states seems to be another mental artifice meant to put order and sense in the world the human mind perceives and tries to understand. What reality may actually boil to is an atemporal labor that permanently raises entropy.
A correction is necessary. When I said that “its different states are real” in the first paragraph above I meant to point out the reality of the permanent change of the universe, whose processual nature is formalized by the human mind as a series of states characterized by temporal succession and cause-and-effect relationships.
You seem to be talking about two different things:
External changes occurring and entropy increasing, regardless of consciousness.
A conscious entity perceiving a present state S[sub]0[/sub] … but having (in the present) the concept or memory of a previous state S[sub]prev[/sub] … and conceiving (in the present) of a future state S[sub]next[/sub].
The first statement is what physicists mean by time.
But you are defining time as the second statement, and then concluding that time only exists in consciousness - which is a circular argument.
Yeah, I don’t think there’s ever much to be gained from declaring something impossible and there’s always a risk that a reframing will show it to be at least hypothetically possible after all.
I’m sure if I traveled in time to the year 3000, and downloaded “Temporal Physics for Dummies” into my brain, there’d be lots of fascinating insights and probably completely different ways of looking at, eg, causality loops that no one in my time has ever thought of.
Maybe the book will still declare time travel to be impossible (and I would therefore disappear :)). Maybe not.
Regarded as a fourth dimension by scientists, time seems to be an inborn human concept (or category, as described by Kant), especially because experiments on infants demonstrate their familiarity with fundamental cognitive notions such as continuity. Continuity, simultaneity, succession are all related to the concept of time and they play an essential role in our understanding of the world. However, there are scientists (like Carlo Rovelli) who believe that the human perception of time does not correspond to reality. This reminds me of my long-held intuition that time is our rather mundane manner in which we can understand and/or describe change and makes me wonder whether in fact the universe is just an entropy generating labor that exists strictly in the present.
I guess the answer to this question is supposed to show something about time, rather than the way I handle appointments. But I have already mentioned the fact that time is an inborn category of our mind without which we cannot understand or describe reality. The issue under discussion is whether this category of the human mind corresponds to an aspect of physical reality and if so which aspect of physical reality we can be talking about. And I don’t think mundane activities can be of much help in this discussion although some people may try to prove that light has no mass by taking a picture of an electronic scale reading zero under the brightest sun.