
The illusion of time - taylodl
https://www.nature.com/articles/d41586-018-04558-7
======
kirse
I always saw time as a way of applying numerical labels to a state of the
universe. In my view, the universe only ever exists in one state, albeit
constantly changing at the "speed" of light. It is our biological capability
to remember past states and envision future states that project this notion of
time into everything.

Time is lodged into almost all of physics because the only way we can do
something useful (not being God and not knowing the absolute equations sans-
units) is to compare present values to previous-present values. That division
sign wedged into every relative unit of measure - kg, sec, meter, etc - is
basically a way of saying "as compared to". Present as-compared-to the-
previous-present. What-is-now ÷ the-remembered-now. Universe-at-Planck-Tick
#145 ÷ Universe-at-Planck-Tick #144

All of the universal constants come down to comparing a present state to a
previous-present state and noticing that the delta between them is a
consistent value. I don't think this is really news to many, but it helped to
make physics and the some of the exotic math behind it make more sense to me.

~~~
3pt14159
The thing that is tricky though is that the changes in state are affected by
the the state's own state regarding the state of the state change.

Put another way:

My writing this comment is changing the state of our universe. I'm writing it
because I perceive the state change. If time is solely illusion then there
would be no difference in the state between Tick #145 and Tick #146, but there
is and it is this comment, which means that the universe (or at least our
universe) is dependant on something that you all say doesn't exist.

I'm not saying you're all wrong, but it is a pretty surprising thing if it's
true and modal realism is false.

~~~
Senderman
State-change received and confirmed. Thank you for updating the universe.

~~~
3pt14159
I am the state.

------
doctoboggan
I think this is a fascinating subject. Time is something we all experience and
intuitively feel exists, yet is remains so elusive to actually nail down and
study.

The Youtube channel PBS Spacetime did some of the best explorations of ideas
in this area that I've heard:

[https://www.youtube.com/watch?v=GguAN1_JouQ](https://www.youtube.com/watch?v=GguAN1_JouQ)

[https://www.youtube.com/watch?v=fHRqibyNMpw](https://www.youtube.com/watch?v=fHRqibyNMpw)

[https://www.youtube.com/watch?v=5l1KxgHH2Ek](https://www.youtube.com/watch?v=5l1KxgHH2Ek)

------
Certhas
Time is an illusion, but by the same token so are space and coffee. So maybe
that's not a useful way to use the word "illusion"....

~~~
joslin01
No not by the same token. Coffee is a physical manifestation. Time is a
perspective or measurement.

~~~
Certhas
I'd like to see you try to define these terms.

~~~
joslin01
Coffee is sitting there as a bunch of molecules. Can you point at time as a
bunch of molecules sitting there? If not, it's not by the same token.

~~~
Certhas
I take your bunch of molecules ("physical manifestation") and squash them into
a black hole. Now they have been turned into an aspect of the structure of
space and time ("a measurement or perspective").

So no, space and time are not "measurements/perspectives" that are
fundamentally distinct from "a bunch of molecules".

~~~
joslin01
Ok so you change the situation drastically by squashing them into a black
hole, something nobody really understands, and tell me coffee and time are
interchangeable. Right.

Also I never said space was measurement/perspective, I said time was. You
believe what you want to believe, but maybe stick to a single scenario in the
future. I'll say it again, a cup of coffee just sitting there is distinct from
time.

~~~
ben_w
While I agree that was a poor example for much the same reasons, I think I
have a much better comparison:

Duration is as much a measurement/perspective as displacement, this is an
observation which led to Special Relatively. If time can be called an
illusion, so can position.

~~~
joslin01
I guess I don't see the equivalence. Time very much depends upon duration and
the terms might as well be synonymous. Does space depend upon displacement? If
we froze a single instance of space & time, we would see a universe sitting
still. Space and all its fillings would still be there but would time? I
believe it quite bold to call space time and time space just because duration
and displacement seem similar.

~~~
ben_w
You’re calling one dimension special because if you remove it you don’t get to
use the special words you use for that dimension.

If updown was a special named dimension and you took a single 2-space+1-time
slice of the universe at fixed radius from the Earth, your argument wouldn’t
really be different, only words and phrases like “sitting still”, which is
inherently _about_ the dimension being removed, because it’s convenient for
us.

And that’s ignoring questions like “can particles have momentum if there is no
time?” which might actually be important in the unlikely event that I
understand what a black hole’s singularly does to time.

~~~
joslin01
I think what you're saying is fair and I realize it might be pushing it to
remove the dimension of time to articulate my position.

Regarding the last question, if I understood forces correctly, it's that they
remain in motion until an equal or greater force stops them right? Why do we
need time for that out of curiosity?

~~~
ben_w
Thanks. Velocity is the derivative of position with regard to time. Does it
exist if there is no time? It might be that momentum is the fundamental thing
and velocity is just a consequence of it. Or not, I don’t know.

Momentum has a direct influence on Einstein field equations, and I don’t know
enough maths to follow GR (just two A-levels) so I have no idea if that
“direct” influence is still present at a no-more-future boundary condition.

My insufficient maths skills are, amongst other things, why I don’t trust my
understanding that a black hole singularity really is a no-more-future
boundary condition.

------
liberte82
When taking hallucinogens and in a few cases without, I've had instances where
my ideas and concepts of time have begun breaking down. It's a very weird
feeling, when you begin becoming uncertain about how or if time works. And
impossible to "grasp" when you're not experiencing it and are back in a
"normal" mindset.

~~~
empath75
If someone were to ask me how long an LSD trip lasts, I would always say:
"Exactly one eternity".

~~~
k__
Reminds me of "The Jaunt"

~~~
dokem
I went and read that today because of your comment. I found it interesting and
frightening in a paradoxically mind bending kind of way. However, it did seem
a bit unbelievable that 300 years into the technology and there were no
safeguards and only ~30 mishaps had happened despite how, apparently, easy it
is to torture yourself.

~~~
k__
Yes, Steven King writes utter bullshit, but somehow he makes it scary like no
one else

------
choxi
> The malleability of space and time mean that two events occurring far apart
> might even happen in one order when viewed by one observer, and in the
> opposite order when viewed by another.

Why doesn't this break the rules of causality? I found this answer on Quora
([https://www.quora.com/Is-chronological-order-of-events-
prese...](https://www.quora.com/Is-chronological-order-of-events-preserved-
for-different-observers)) but I don't understand it.

~~~
whb07
It doesn’t break the rules of causality because they arent even related. Let’s
say I poke a balloon with a needle, the poking event causes the balloon to
pop. The pop will never ever occur without me first poking it, irrespective of
any number of viewers across all possible distances.

Now for the distortions in time perception, it does matter as to who the
viewer is. Everyday you wake up you experience energy that’s being radiated
from the Sun that’s roughly 8 minutes away (at the speed of light).

And yet, there’s cosmic events which have released energy that have happened
millions and millions of years ago which have yet to reach us because we are
so far away. So from our perspective the Sunlight from today is an older event
than the truly much older supernova explosion that has yet to reach our
planet. That which when we finally detect it, it will be a “new” event which
again is much older than our Sun.

~~~
glitchc
Your example belies the very core of the argument in the article, in that the
sequence you just described as causal is in fact an illusion.

Certainly from the human perspective, these events in sequence look causal.
But our perception of time is finite and our mind is constructing the order of
those events. But the human perspective is subject to the limitations of our
sense of scale, our faulty sense impressions and our faulty logic in
reconstructing those events.

At the scale of molecules, the distances between the molecules of air, the
rubber of the balloon and the metal of the pin are vast. It is impossible to
perceive, looking at a subset of molecules of air within the balloon far from
the site of the pinprick, why the molecules of metal interacting with the
molecules of rubber have any effect on the molecules of air around them. There
is no correlation.

Going deeper, at the intra-atom scale, it is difficult to fathom an
incontrovertible connection between cause and effect when two atoms interact,
as mostly empty space encounters mostly empty space. That their nuclei are
close enough to influence each other is determined probabilistically, not
deterministically. The odds that any two atoms interact is quite small. The
probability improves with their relative number and density in a given volume
of space and gives us some measure of reliability that we treat as causality.

~~~
21
Atoms are not mostly empty space, because electrons are not little balls
spinning around like planets.

Electrons are more like continuous clouds surrounding the atom.

> The picture of an atom being mostly empty stems from the childhood of atomic
> structure analysis, where most of the atom's extension was found to be
> transparent for alpha rays, and the early models explained that by pointlike
> nuclei and electrons. Similarly the picture of a proton or neutron being
> essentially empty apart from three quarks embedded in it arises because deep
> inelastic scattering shows that protons are essentially transparent for very
> energetic electrons, except when the latter meet an almost pointlike quark.
> But both pictures are quite limited: We don't think glass doesn't occupy
> space because it is transparent for light.

[https://www.mat.univie.ac.at/~neum/physfaq/topics/touch.html](https://www.mat.univie.ac.at/~neum/physfaq/topics/touch.html)

------
codeulike
The End of Time by Julian Barbour said something similar.

[https://en.wikipedia.org/wiki/The_End_of_Time_(book)](https://en.wikipedia.org/wiki/The_End_of_Time_\(book\))

Its interesting, the but the picture of reality that it conjures up is
ultimately a bit of a stretch, in my view. Kinda creating a bunch of new
problems just to try and get rid of the time problem. If it was a code
refactoring, it would strike you as a questionable one.

------
dstroot
Based on relativity photons do not experience time. They “hit” something the
instant they are created - even if we perceive them to have existed for
billions of (light) years.

~~~
liberte82
From the perspective of a photon, everything in the universe is happening here
and now.

~~~
doubledad222
Is this _REALLY_ accepted as true? Photons are fast, but they're not
instantaneous. They still take millions of years to travel between galaxies.
For something to be truely timeless, I'd expect it to be able to teleport. Is
this incorrect?

~~~
cuspycode
Assume a really fast rocket is traveling from galaxy A to galaxy B. Due to
relativistic length contraction, the distance between the galaxies is less as
seen by the rocket than it is for a stationary observer in either galaxy. So
the travel time from the perspective of the rocket (the "proper time" of the
rocket) is less than the travel time measured by a stationary observer. And
when you work out the math, the rocket's proper time approaches zero in the
limit as the speed of the rocket approaches light speed.

------
lisper
I made basically the same argument four years ago:

[http://blog.rongarret.info/2014/10/parallel-universes-and-
ar...](http://blog.rongarret.info/2014/10/parallel-universes-and-arrow-of-
time.html)

It's actually pretty obvious once you understand how entanglement and
measurement are related, i.e. the are the same physical phenomenon.

~~~
kgwgk
> You can remember the past and not the future because whatever you remember
> is your past.

Conveniently enough, this direction of time coincides with the one where the
fusion of hydrogen atoms into helium in the Sun emits radiation (rather than
the alternative direction where the Sun absorbs from the space exactly the
radiation required to fission helium atoms to obtain hydrogen), the one where
separated gases mix (rather than the alternative direction where mixed gases
separate spontaneusly), coffee gets cold (rather than hot), etc.

~~~
lisper
It's not "convenient", it's necessary. If the sun absorbed radiation in this
way, you would not be able to see it. You can only receive information from
photons that you absorb (and hence are emitted by something else), not from
ones that you emit and are absorbed by something else. That's why you can
never see a black hole.

~~~
pdonis
_> If the sun absorbed radiation in this way, you would not be able to see it_

This isn't an explanation, it's just a restatement of the problem. The
radiation process itself is time reversible: the case where the sun emits and
your eye absorbs, and the case solution where your eye emits and the sun
absorbs, are both valid solutions of the equations describing the physical
laws. Saying that the eye has to absorb radiation to see it just restates the
fact that, in our actual universe, we do in fact see the sun by our eyes
absorbing radiation--i.e., that that solution of the laws is the one we live
in. It doesn't explain why that solution of the laws, and not the time
reversed one, is the one that's actually realized.

~~~
lisper
> This isn't an explanation

Yes, I know. It wasn't meant to be an explanation, it was meant to be a very
specific and narrow response to a very specific comment. The full explanation
is in the article I linked to above, which is too long to reproduce in an HN
comment.

~~~
pdonis
_> The full explanation is in the article I linked to_

I'll take a look. I see that it's several years old; if I have comments,
should I post them there, or here?

~~~
lisper
As you wish. Comments on old articles get moderated, but they still get posted
(I just have moderation turned on as an anti-spam measure). And a fair number
of people are subscribed to my comment stream so you may get better feedback
there.

------
8bitsrule
"When his lifelong friend Besso died. Einstein wrote a letter to Besso's
family, saying that although Besso had preceded him in death it was of no
consequence, '...for us physicists believe the separation between past,
present, and future is only an illusion, although a convincing one.' "

[http://everythingforever.com/einstein.htm](http://everythingforever.com/einstein.htm)

------
karmakaze
A good analogy I like to use is 'time legs'. Imagine if you were a leaf
falling from a tree, being blown about the ground and air. You would be in
3-space but only experiencing it as a passenger. A leaf as no legs. We lack
'time legs' and if we had them, we would realize that time isn't a special
thing.

------
wuliwong
The author's physics might be real science but this seems like semantics to
me. In addition, the idea that "time is an illusion" is equal parts physics
and psychology. While the author maybe a professional physicist, I doubt they
are much more than an armchair psychologist.

------
dmfdmf
Time is an illusion, freewill is an illusion, etc. are all attacks on and
denials of consciousness. The fact is that consciousness exists and has
identity. In the past consciousness was treated as supernatural but the
"modern" attempts to deny it are no less irrational.

~~~
21
Physics hasn't still decided if our universe is completely deterministic or
no, if all the apparent quantum randomness was not already determined (think
about a seeded random number generator).

You are trivializing a very deep question:
[https://en.wikipedia.org/wiki/Superdeterminism](https://en.wikipedia.org/wiki/Superdeterminism)

~~~
AnimalMuppet
OK, but "the universe is not completely determined because of quantum
randomness" != "I have free will", or even "consciousness is real".

------
dustfinger
> He posits that reality is just a complex network of events onto which we
> project sequences of past, present and future.

I wonder if the "we project" part is the author's choice of words or Carlo
Rovelli’s. It is not explained and therefore has not definitive meaning.

------
hi41
There was a post on the 13.7 blog at NPR. It said that it is ok incorrect to
think of time as an illusion or an emergent property and that scientists are
doing a disservice by doing so. Time is real it said. I looked but couldn't
find that article.

------
joslin01
Happy to see my passing thought "How can time be real?" is actually being
given serious academic study.

If you take reality to be right here, right now (what else _could_ it be?),
time cannot exist, it just helps us map change.

~~~
codeulike
So how does change happen?

~~~
joslin01
One reaction at a time in a chain of reactions. If you lift your arm up, are
you asking me how did that happen? Muscles fired to go from point A to point
B. I'm confused by your question to be honest; are you telling me change
occurs _because_ of time? Or trying to tell me change depends on time? Then
yes, but change is just a perspective as well. There's only ever going to be
right here, right now.

~~~
codeulike
What I mean is, if there is only ever right here right now, that is a frozen
timeless state, and how do you traverse from that to some other different
state.

------
qwerty456127
I have always been perceiving time just this way. What the article describes
seems just obvious while fitting in the common model of time an schedules is
rather hard and always very stressing for me.

------
axilmar
It may be that time does not exist, but the universe certainly does have
states, which are deployed simultaneously (hence time is an illusion). But
this means the universe is 100% deterministic.

------
jpmoyn
While I can understand the basic concepts behind theories like this, I much
prefer to live in my very human bubble of ignorance. I just don't feel like
dealing with the existential dread.

------
IloveHN84
That's why I need a 48h long day? 24h seem too few for me

------
bobthechef
If time did not exist in some fashion, then change would be impossible. Remove
time and everything is simultaneous or eternal. What we say _was_ or _will be_
exists along with all we say presently _is_. Naturally, this leads to a
contradiction. Imagine something moving along a trajectory that was at
position p1, is at position p2, and will be at position p3 is now in all three
positions. Add another object on an intersecting trajectory. A collision
occurs when two objects are at the same position at the same time. Without
time, these objects are both colliding and not colliding.

~~~
SiempreViernes
Draw two crossing lines: the lines are mostly not touching except at the point
they cross, so they are both touching and not touching depending on where you
look. Is this a contradiction?

~~~
bobthechef
At the POINT of intersection. Those objects are both at the point of collision
and not at the point of collision.

~~~
SiempreViernes
The same is true for the crossing lines: they are both at the point of
crossing and at all the other points along their length.

------
emodendroket
This is strangely reminiscent of the part of Saint Augustine's Confessions I
found the most trying to finish.

------
pcurve
I wish all mobile sites were as beautifully designed and spaced as this one.

------
carapace
What is the duration of "now"?

~~~
Senderman
Seems infinite so far.

------
creaghpatr
The past is a faulty memory and the future is an illusion of ego.

~~~
AnimalMuppet
So if I had a good memory, there would be no past? I don't buy it.

Or, _all_ memory is faulty, and that's all we've got of the past? In that
sense, this might be true.

------
chaoticmass
Time is an illusion. Lunchtime, doubly so.

~~~
mattkevan
Very deep. You should send that in to the "Reader's Digest". They've got a
page for people like you.

~~~
fzzzy
It’s a quote from Douglas Adams.

~~~
deadmetheny
That is also a quote from Douglas Adams. It's literally the following line
from the original quote.

~~~
Senderman
He was riffing - the 3rd line is "It’s a quote from Douglas Adams."

At least, as it appeared in the comments on HN.

