This is actually a contradiction. Either the state isn’t the same (ergo, no loop) or the end leads to a new beginning (ergo, no final death).
~Max
I’m saying, in a looping universe, we agree that the distinction between t=1 and t=101 is meaningless, because the state of every particle in our pocket universe is the same at those two times.
But time does exist in this universe, because we are going from our state at t=1 through various other stages all the way to t=101 where we are back where we were.
But let’s say instead of 100 distinct positions 1 planck time apart, 2 we only have two distinct positions. Particles in our universe have one position at t=1, another at t=2, and at t=3 they go back to position 1.
This universe still has time, but only two positions. t=3 is identical to t=1.
Now let’s say our universe is instead completely empty. No particles in it at all. How can we say that time passes within this universe when there is literally no frame of reference to base time off of?
The same applies to a singularity universe that’s completely full of matter and energy. If every point in the universe is equally full of mass and energy, then there is no flow of matter, no interaction between forces. There can be no time.
Only in a universe like ours, where matter and energy are irregularly distributed, can we have time; and time marks the flow of our universe from one state (almost but not quite full of energy, as our universe was 1 planck time after the big bang) to its eventual heat death.
Talking about time before the big bang doesn’t make sense, because time did not exist until the big bang expanded the universe and created an energy gradient.
Talking about time after the heat death doesn’t make sense either, because time will not exist when there is no more matter/energy/change in the universe.
Now look, heat death does not imply absolute nothingness. Conservation of energy is still a thing. Absolute zero isn’t a temperature the universe will actually reach, it’s an asymptote of sorts.
So time will still have meaning, in the same way that x in y=1/x still has meaning no matter how high you go for x.
~Max
That depends on a few factors:
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does dark energy remain constant, or increase the more the universe spreads out? If it will increase, we could be looking at a “big rip” scenario, where eventually subatomic particles are torn apart from each other by the expansion of the universe. In that scenario, conservation of matter means you will eventually end up with each subatomic particle floating all by itself in an observable universe that’s completely empty aside from it. Which means that particle won’t be able to interact with anything else, so time is meaningless.
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it is possible that matter itself has a half life, which will eventually lead to it decaying into energy, which will eventually dissipate into the universe. You’d end up with individual photons of incredibly low energy each in its own observable universe. Again, time is meaningless.
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even if neither of the above is true, 1/x can never equal 0 - unless there is a finite limit to how small we can go. And we do believe that energy, like matter, should come in discrete chunks - as far as I understand, at least. So if the total energy of the observable universe gets to that point, that’s heat death.
Of course, under quantum mechanics, that’s not a zero energy system either, because you’ve got zero point energy coming from quantum interactions. But here’s the problem with zero point energy: it is basically meaningless. Because that energy is everywhere, at all times, equally, there is no energy gradient and no energy can be extracted. Sort of like the pre big bang singularity that contains all matter and energy. It doesn’t matter how much energy is being generated by the quantum foam if that energy is literally everywhere. So that doesn’t give us time, either.
That’s not a fact, it’s an opinion. Gravity, to my knowledge, has infinite range. (This is another infinite for the OP)
Right, that’s why I said conservation of energy and not conservation of matter. Even null dust has a stress-energy tensor.
Admitted. My point is that f(x) there is no upper bound on positive x and f(x) is always less than f(x+1). Infinite domain, and still meaningful.
~Max
Gravity may have infinite range, but its impact spreads out at the speed of light. Once something is outside the observable universe, we can no longer be impacted by its gravity.
In order for gravity to have infinite range, wouldn’t there have to be an infinite distance for it to act through?
In the same way that the electromagnetic field has infinite range.
IOW, it can only affect things within the future light cone of whatever is creating the gravity.
Energy is not really conserved, in two ways. The first is the more familiar idea of energy, the ability to do work. In that sense, energy is consumed, as there is less and less work that is able to be done with the amount of energy left.
The specific idea of energy, the energy that is conserved, is still not conserved in that it is diluted by increasing amount of space. The universe as a whole does not observe this rule, only parts of it that are smaller than it. IOW, any region of spacetime will have less and less energy in it as time goes forward.
Eventually there will be no dust, only photons.
And eventually those photons will have the lowest possible energy state, and be so far apart that light speed wouldn’t be fast enough to cross the expanding space between them. That would he heat death.
Yes and I have made this same suggestion elsewhere. Based on the fact that from reading Steven Weinberg’s First Three Minutes it seems to me that as much changed between 10^-45 seconds and 10^-44 as between 10^-44 and 10^-43 and therefore that time should perhaps be viewed logarithmically. So everything would be very tiny and move very fast. Just the opposite of what happens later on. From that point of view we are at logarthmic time between 17 and 18 (using the age of the universe in seconds, a totally arbitrary unit).
Would complex interactions necessary for life be possible under those conditions? What would be their medium?
And eventually a photon will be surrounded by a patch of space that nothing else is within its future light cone. What happens when its wavelength gets longer than its light cone, where it effectively is no longer able to communicate across its own existence seems to be an interesting situation.
Most patches of space won’t even have that. But they will still have the virtual particle foam. Stuff will still be happening at that level of reality, even if none of it results in any sort of stable particles.
Space will never be perfectly flat and featureless, and instabilities in such a situation could lead to exactly the same conditions that set off the big bang in the first place.
If you have a big patch uniformly inflating, and then one bit of that is inflating just a bit slower than the rest, then suddenly, you do have something interesting going on, and you essentially have a patch of space that is projecting a gravitational force on the rest. That could collapse, and the energy involved in that collapse could kick off a whole new universe.
It would not be life as we know it, but it would be very complex. If that means that intelligent beings could evolve, who knows, but the subjective time of interactions would be such that something that only existed for 10^-44 seconds could have the same subjective passage of time as billions of years for us.
I’m just not comprehending how something can permanently leave the observable universe. If, for example, a distant galaxy was to recede from us faster than the observable universe grows, I would expect to see it blink and then blink slower and slower due to redshift. I would not expect it to ever stop blinking on account of distance, even if the period grows to billions of years. And like so with the propogation of gravity and gravitational redshift.
~Max
So the fastest that two objects can move apart from each other is the speed of light, because accelerating faster than that in any reference frame is impossible.
But that’s for moving THROUGH space, like you would if you were in a spaceship, or like the sun is doing. But galaxies don’t get further apart because they are speeding apart through space. They get further apart because on that enormous scale, space itself is expanding.
Don’t think of the big bang as an explosion that happened and stopped. The big bang is the time when space started to expand, but it has never stopped.
If you have two objects - say, galaxies - and they are stationary relative to each other, then they will move towards each other due to gravity. Very slowly at first, but as they get closer, they accelerate faster.
But now let’s say that space itself is expanding, not from a central point where the big bang happened, but EVERYWHERE. So the amount of space that the two galaxies have to cross is constantly increasing.
For Earth and the Sun, or the Sun and Alpha Centauri, this increase in space is so miniscule that gravity, weak as it is at a distance, can keep them together despite the expansion of space.
That’s even true of the Milky Way and its neighbors in our Supercluster.
But beyond that, other galaxies are so far that instead of slowing down and eventually coming back towards us due to gravity, they are accelerating away faster than the speed of light.
The classic analogy is a balloon with points painted on it. As you blow up the balloon, the points move further apart, not because they’re actually moving but because the surface of the balloon is expanding.
Well, let’s consider how fast the balloon expands. Imagine you live on the surface of a giant balloon, around a star that’s painted on its surface. You decide to travel to the next star over, and set off at close to the speed of light.
But as the balloon blows up, you find that the balloon carries the destination star away from you faster than light! How can this be?
It’s because the further apart two objects are, the faster they move apart, because there is more space between them, and all space is constantly growing.
And since the objects aren’t moving away from you THROUGH space, but are instead being carried by the expansion of space, there’s no speed limit there, and eventually they disappear over an event horizon.
In other words, the universe isn’t only growing at the edges. It’s growing EVERYWHERE. Locally (ie in our galactic supercluster), gravity keeps matter together, but further than that the expanding universe creates space faster than light can cross the distance involved.
Yes, I understand that. I did not mean to imply that any particular object moved faster than the speed of light, only that they recede faster. I see that there’s a point where an object can move so far away that it passes an event horizon, but I don’t think the sky will ever go completely dark forever. We will always be recieving the CMB, for example, although eventually they will be redshifted so much that you might need a planet-sized dish and multiple years to catch one photon.
~Max
the cmb is just photons.
They will redshift until they too have wavelengths greater than the size of the observable universe, and they too will find themselves isolated from any others.
The sky will go dark, and unless there is some form of rekindling, ala conformal cyclic cosmology, it will stay dark.
So? Just because the wavelength exceeds the size of the observable universe, does not mean interaction is impossible. For example, some military submarines can recieve radio signals which are broadcast at about 3Hz at 300,000km/s, which means the wavelength is something around half the diameter of the Earth.
ETA: Normally the interstellar medium would block this kind of low-frequency radio wave, but in this heat death scenario, the interstellar medium is gone.
~Max
I’m not sure what you mean by ‘interacting with time’, here, but if it’s just ‘experiencing one moment after the next after the next’—then no, that’s still not right. A temporally infinite entity will not have experienced an infinity of moments passing one after the other, because there are no two points in time on the timeline of such an entity between which there are infinitely many moments (provided a moment is something of finite duration, like a second, billion years, or Planck time). If, at any time in their history, they start a clock, then it will have only counted up a finite amount of seconds up to the present point. There is no time on their timeline such that they could’ve started counting and reach infinity, nor will there ever be.
Besides, your argument, which I’ve up to now simply assumed as sound, is highly questionable: in most standard models of time (that is, in all models, save for some highly speculative theories) time is continuous; thus, between any two moments of time, there are infinitely many moments (here as ‘temporal instants’). So you’ve just experienced an infinity of moments between reading this part here and this part here, and it was no trouble at all.
A temporally infinite entity gets older by one year every year, just as we do. It’s just that adding one to infinity doesn’t increase infinity. This isn’t different from how there are just as many odd whole numbers as there are whole numbers in total. It’s a failure of our ordinary instincts regarding quantity to apply, to be sure; but nobody ever told either math or the universe it had to conform to your instincts.
Besides, you’re already accepting infinite process—such as the infinite cycle of Solomon Grundys. But really, pretty much any complex being is better modeled as a process than as something that simply persists—take, for instance, the process of cell renewal: our cells are born, live, die, and are replaced by another fulfilling the same function (or we may, for simplicity, stipulate this to be so). Of course, they don’t do so all at once—maybe a million cells die every second. The oft-quoted figure is that our cells are replaced, tout court, within seven years. That may or may not be true, but let’s assume it is: then, just make every cell lineage in a body a Solomon Grundy, and presto, you’re done—the entire being will be temporally infinite.
But of course, it doesn’t need such shenanigans. If the universe can be temporally infinite, then there’s no reason for any part of it not to be, too. And that the universe can be temporally infinite isn’t seriously in question—in fact, many people argue that eternal inflation is the most simple model in accordance with current data. This isn’t falsified by somebody pointing out that you can’t count to infinity. I mean, c’mon.
And such an eternally inflating universe will include infinitely many objects—it will include infinitely many regions where inflation has stopped, giving rise to patches like our own universe. There will be infinitely many planets, stars, tapeworms, and Coca-Cola cans (with probability 1), and that you can’t count them won’t bother them at all. Here’s astrophysicist Ethan Siegel laying out the general reasoning, if you’re interested.