1) A term doesn't become imaginary just because it turned out to be physically more elaborate than its initial meaning.
The concept of time never vasnished. It just changed a bit. It is still one of the axes of spacetime.
2) The logic itself is flawed. Saying "Time might only exist in your head ... because of spacetime" is like saying:
* "Magnetism might only exist in your head ... because of electromagnetism"
* "Electricity might only exist in your head ... because of electromagnetism"
* "Atoms [meaning: individable parts] might only exist in your head ... because of electrons/protons/neutrons"
3) Even from a purely philosophical view, pointing out time here is meaningless. Every word describes a concept, a model, so anything including spacetime might exist just in our heads. Pointing that out specifically for time makes no sense.
Think of it in the same way that there's no green and red (the colors), just frequencies in the electromagnetic spectrum, that we just perceive as green and red.
I'm just a layperson reading this article - happy to be corrected.
But even then, this would imply that our forward/backward time direction is just convention, much like left/right space directions.
Yet, isn't it strange that all human cultures have developed the same notion of the forward time direction? Wouldn't we expect some islands to have developed the other convention, just like there are some places where cars drive on the left rather than right side of the road? Or, is it our human brain? Then, shouldn't we observe some animals or plants with an apparently different perception?
More importantly, however, this disagrees completely with physics, ancient as well as modern physics, because of, well, experiments.  The forward/backward time directions are more comparable to up/down space directions (in a gravitational field), which are very distinct from each other. The direction of time can be measured in so many different ways, almost none of them really connected to our personal perception.
It's the whole world around us that makes a clear difference between forward and backward time direction, not just we in our heads.
 Those led to the discovery of the second law of thermodynamics, which modern physics does question in its fine-grained details (as with gravitation, etc.), but not in principle, because it is so clearly visible in experiments. https://en.wikipedia.org/wiki/Second_law_of_thermodynamics
 See also: https://en.wikipedia.org/wiki/Arrow_of_time
The question of time's arrow is an old one. And to be clear, it's not whether time exists, but what direction it moves.
Lanza is the founder of biocentrism, a theory that space and time are constructs of biological sensory limitations.
- everything we see in universe is essentially because of a personal predisposition towards seeing time a certain way. Even the 2nd law is because we see time the way we do.
If time is a lie, then all physics becomes a lie.
Btw, I'm going to stop digging now. I have no idea of what I'm talking about except what I read in the article.
This "theory" is old and well-known.
However, we are not merely limited by our (biological) sensors, but by our sensors+actors.
That is, we can't see too far in the sky, but we can build telescopes. And microscopes. And other strange machines with whom we interact mostly by looking at numbers those spit into some computer. Science has long overcome our biological limitation, and is more driven by our technological limitations: What if our computer programs which evaluate our experiment's sensory data are wrong? What if the CPU is defect? Or the wiring with the sensors is bad? Better take some more computers and let them calculate the stuff again. And take some more humans to evaluate everything. And better repeat whole experiments from time to time. But that's what we are doing (or least: know we ought to be doing) all the time.
There's a lot to criticize here with design of studies and repeatability of experiments, but our biological limitations play a fairly small role here.
If energy cannot be created nor altered, only change forms, then time seems to be quite arbitrary.
Take money. Think of money as your economic energy. It can change from coins to bills to T-Notes. It can be dematerialized into an accounting entry or a whole lot of Satoshis but ultimately money is just your economic energy.
To track it in your head, you timeline it - my employer/customer owned N units of money earlier, now it belongs to me as a banking entry, later I will convert it to bills to buy a goat etc etc. You may create all sorts of elaborate theories regarding money. There may be tight mathematical rules governing the transformation of money from dematerialized form to bills e.g., your ATM demands a PIN to do the transform which is completely arbitrary as far as money is concerned.
All through these changes, money hasn't changed form at all.
To tie it back to the original piece, energy is mass. Your electron waveform which we interpret as mass is energy. Once we started tracking it, we had elaborate rules (laws) to describe its behaviors but ultimately, it's just energy.
While we are observing the energy, it behaves a certain way which follows all the rules of physics..but much like the ATM and PIN rule, the rule is not relevant to the energy.
Likewise, your need to understand a before and after state for energy forces you to invent time. For example, if you never transformed your money in the bank into bills, as far as your bank account is concerned, no time has elapsed.
> But even then, this would imply that our forward/backward time direction is just convention, much like left/right space directions.
Isn't just the whole Prigogin/Einstein argument ? (small scale gives the illusion events are rewindable vs higher scale givea the illusion events aren't rewindable).
But the whole "time doesn't exist without an observer and observers create time" just seems to be begging the question. An observer with a brain has an arrow of time, because otherwise the brain doesn't have a past and can't make memories- how can you make a memory without an arrow of time? Observation seems to be an irreversible process. But brains are made of stuff, that stuff obeys the laws of physics, so where do observers come from in this theory?
During such a drunken conversation I'd simply say "so when a car hits me because I misjudged the right moment to cross over, the pain is only in my head and it doesn't exist?" and would laugh.
That's exactly how much value I see in this article. It says absolutely nothing of substance. It doesn't even have philosophical value.
Well. The physical pain would indeed only exist in your head and your head only :).
/pour me another.
/winks and raises a glass.
Repeating a tired millennia old argument that crudely stops any inquiring talk for anything that's not directly measurable (and/or doesn't translate into money or some direct benefit)...
But while the grandparent started with "As a physicist", as if this conveys the consensus among physicists, they forgot to mention that many physicists (including celebrated physicists) are indeed very interested in the meaning and the philosophy behind physics concepts, and there have been excellent forays into such matter, without going into BS Chopra territory.
I wasn't trying to convey any "consensus" among physicists, merely make abundantly clear that the specific article in question does not appear to contain any discernible novel scientific or philosophical content. You're perfectly right in saying that plenty of great physicists are indeed interested in the philosophy of science (though many more are not), and that's fine. This article and the ideas it represents aren't a part of that.
However, this particular discussion (in the article) is indeed very old and nothing productive ever came out of it, I think. It's almost like asking "what's the meaning of it all?"
Something I'd be interested in reading would be a theory in how the human brain "slows down" time when we're in severe pain, or what known quantum effects might contribute to time dilation caused by us without going to a black hole. Etc.
You know, something that is still not a solved problem but has an attached practical question to it, instead of "what if time only exists because we're designed to perceive it?", which really says nothing at all.
All of this is an opinion of course.
"The punch line is this: the statement that we can't time-travel into the past is exactly the same as the statement that we can only remember the past. It is not the case that one causes the other, it is that the two things are logically equivalent. Your perception of "traveling through time" emerges from your mental states and not the other way around. You feel like you are "traveling forward through time" because your mental states have this natural order to them. You can remember the past and not the future because whatever you remember is your past. The laws of quantum mechanics (and entanglement in particular) insure that what any given instance of you remembers appears to be a continuous and coherent sequence that behaves according to regularities that we call the laws of physics. But in fact you do not travel through time, because at root there is no you, and there is no time. There is only the wavefunction, from which both you and time emerge as an approximation."
I wonder if we're just playing at semantics and what "time" means to me is not what "time" means to quantum physicists. Clearly events unfold in a linear fashion and we cannot rewind time like a movie and go back to exact events that have occurred in the past. But "time" defined as a fundamental force of the universe may be something entirely different, perhaps intertwined with quantum probability.
Maybe this is how we'll eventually solve faster than light speed intergalactic travel. Instead of manipulating space, we'll manipulate time - i.e. travel to a point in time where we probabilistically exist at that location in space. Of course, once we get there, our perception of time moving in a linear fashion will "speed things up" to the current time as perceived by all of us.
I know it's kind of facetious, but we can't flap our arms to fly either, and that doesn't mean that gravity unfolds in a linear fashion and we cannot rewind its direction.
Things get a lot simpler if you don't believe in free will. Maybe you could observe the past or future through some experiment that we haven't figured out. But you also wouldn't be able to change it. It just is, like space.
A lot of time travel fiction takes that sort of view; plot twist, all of the protagonists' efforts to change the future they saw actually wind up leading them straight to it. Gasp!
The Wheeler-DeWitt equation is covered at about 40 minutes in, here.
Say a decohered particle reaches an un-decohered state outside the realms of our detection. Does this mean that for that particle time didn't elapse? As far as the particle is concerned, someone observed it and then someone was unable to observe it.
This hinges on whether a decohered particle can go back to being undecohered.
If the answer is that particles can stop decohering, then our status as observers is merely a contrivance for us to checkpoint a before decoherence state and a decoherence state.
"Although the equation doesn't include a variable for time [...]."