Occurs when there is no temperature difference in the Universe.

The absolute temperature may be any arbitrary value, the problem is that according to the laws of thermodynamics energy can only appear when the heat flows from a hotter substance to the colder one.

No temperature difference, nowhere to take energy from, no motion, no life, no anything.

This will happen if the Universe expands indefinitely. On the other hand, it might start contracting after reaching a certain size. Stephen Hawking once believed that when this happened entropy would reverse, broken things would fix themselves, time would run backwards, etc., etc. When he did the relevant calculations, however, it didn't pan out. He has called this his greatest blunder.

When considering heat death, the important thing is not to consider the temperature, but instead the temperature gradient and differences in potential energy.

As an ordered system (i.e., well-divided) flows towards chaos, the amount of work that can be extracted from such a system decreases. By the second law of thermodynamics, you cannot have any sort of release of energy without increasing the amount of chaos (entropy) in the system. Therefore, when the system is compeletly chaotic, that is, there is no gradient of potential energy within it, there will be no possibility of work being done within that system. Given that the Universe is a closed system, heat death is inevitable.

If it makes you feel better, just think that by the time heat death becomes a problem, humanity will be long dead, decomposed, and forgotten. OK, so maybe that doesn't make you feel any better.

Some people believe that black holes may be a way around this problem, but I can't give a good explanation why. I believe it has something to do with the fact that the gravity well of the singularity creates a nucleus that is hotter at it center than thermodynamics predicts.

From a really cool timeline at pbs.org, based on recent discoveries that not only is the universe expanding, but it's also accelerating in its expansion due to 'vacuum energy'...

3,000,000,000 years in the future, the Milky Way will collide with the Andromeda Galaxy, either combining into one large galaxy, or ripping each other apart.

100,000,000,000 years from now, galaxies that aren't gravitationally bound will start to disappear... that is, they'll be so far away, we won't be able to see them. Of course, the sun will have burned out by then and the Earth will be gone, but still...

At 1,000,000,000,000 years, the last of the stars will have burned out, ending the Stellar Era we're currently in. The Stellar Era gives way to the "longer, lingering death for our Universe." known as the Degenerate Era.

The Degenerate Era lasts until... hold on, let me make sure there are enough zeros... 10,000,000,000,000,000,000,000,000,000,000,000,000 years from now. The only energy remaining will be in the form of proton decay and particle annihilation.

Energy continues to dissipate until (Scientific Notation used for clarity) 10^100 years (nice round numbers, huh?). At this point, the Dark Era begins. Black holes will have completely evaporated, and the only remnants of the Universe will be "neutrinos, electrons, positrons, and photons of enormous wavelengths."

Creepy, huh?

There may be a quicker way.

There may be a mechanism by which the fabric of the Universe can be spontaneously rent, in the form of a collapse of probability functions of the particular quanta that make up our or any other local universe. This would "appear" as bubbles of total vacuum exploding continuously outward into the local space and devouring everything their wavefront crosses at the speed of light.

No warning. No escape.

Moving Wave of Cease-to-Be (+∞, +∞).

I don't think any of the other writeups actually explain the concept clearly.

The way I think about it is:

  • Any time energy is used to do something, some of it gets wasted due to the laws of thermodynamics. For instance, when you push your mouse across the mousepad, some of the energy is wasted on the friction of the mouse on the pad. This energy is bled off into the surroundings as heat.
  • Due to the pesky laws of thermodynamics, this waste heat cannot be used for useful work. In order to use heat to do work, you need to have heat move from something hot to something cooler. When the whole universe is the 'hot' source, where do you move it to?
  • And because the total amount of energy + mass in the universe is constant, and there's always some energy being bled off as useless heat energy,
  • Eventually, everything becomes useless heat energy

    Happily, all this will happen so far in the future, neither you nor your kid's kid's kid's kid's kids will have to worry about it.

"The calculations" rr speaks of require various assumed constants, including the very unknown mass of the universe. There is no way to truly know if the Universe will eventually collapse or not, because we have no idea of how massive it is, how old it is, or how old it will be before reaching either heat death or the point of collapse towards singularity. We can easily talk about how it's currently expanding and even accelerating away from itself in every direction right now, but who's to say that this ten-twenty billion year point is but an infinitesimal fraction of the lifetime of the Universe; who's to say that this is still the big bang, the Universe is still exploding, as we speak -- it simply has not cooled down enough for us to really understand what will happen to it 10^1000 bazillion years from now.

Most heat death supporters use the laws of thermodynamics to support their claims. I use the same laws to argue against them. The second law of themrodynamics states that entropy will "always" increase and temperature will always decrease as energy is distributed outward (until it reaches a point where everything is of equal temperature); yet we are also told that a state of absolute zero can never exist. We are told that matter will gradually thin out and dissipate until it has run out of energy (or it will infinitely approach running completely out of energy, but never reach it), that there will be no more usable energy left to do work.

Another thing we don't know is if there truly is a fundamental particle. If not, then there are infinite possibilities of low-energy particles that can be the last tiny bits, nearly motionless particles to move towards the state of heat death. The temperature gradient would inevitably drive temperature to approach absolute zero as entropy increased and the Universe expanded ever more, cooling it down by increasing its volume.

How many times can matter divide (or degrade) before it completely decays into nothingness? As the laws of thermodynamics state, neither matter or energy can be created or destroyed, they can simply be transformed into different proportions of each other. Pure annihilation reactions involving anti-matter inevitably create high-energy photons, often gamma rays (e.g. when a positron and electron escape from a black hole and create two gamma rays of Hawking Radiation). I contend that photons represent the physical manifestation of entropy; they travel at the speed of light, faster than anything else, making them useless unless they smack right into something, yet they are always traveling "away" from their origin. A very small number of them collide with matter and lose some of their energy, but inevitably continue on their course, slightly altered but still "away" from their origin (except in a black hole, of course). Every chemical reaction creates some light; often it is re-absorbed by the electrons in the chemicals themselves, but there will always be some loss, sometimes visible, sometimes not. "Heat" is light; specifically the infrared spectrum.

I also contend, just as physicists "contend" when they assume some arbitrary quantity of matter into their calculations, that during the big bang some immensely monstrous quantity of energy was instantly transformed into light, which we now faintly observe as cosmic background radiation. We do know that a significantly large portion (90% or so) of the remaining physical matter was quickly cooled (but by what scale?) and converted into hydrogen, a gas that conveniently burns cleanly to produce prodigious amounts of light. The observable background radiation that seems to radiate away in all directions may have been all gamma rays at some point, but as light travels it ever-so-slowly slides down the spectrum. Who knows, maybe 99.9999999% of the Universe's mass was instantly lost in the form of entropy, yet it's still going to take many, many, many, many aeons, epochs, millennia, bazillion years or whatever (it's all arbitrary in our can't-comprehend-a-million minds) for the Universe to use up whatever smidgen of energy it still has. And if 99% of its mass is converted into light, there will be a continual pull of gravity from the outer reaches of the Universe towards whatever matter remains. Light is affected by gravity and therefore has a gravity of its own; for all we know the acceleration of the expansion of the Universe is driven by cumulative gravitional forces exerted by mere photons, or by photons released by "virtual particle" reactions found in "empty space."

For all we know, the laws of thermodynamics may change at some point. If they don't, the final result is a Universe with no usable energy, and therefore no motion (even photons decay), with an impossibly low temperature. No energy means no matter means no laws of thermodynamics. So do they (the laws) collapse, or do they reverse? NO ONE KNOWS, DAMNIT. If everything actually reaches a state of perfectly equal temperature, even entropy (heat) itself is destroyed, as to stop a photon is to "annihilate" it, and to equalize all temperature is to halt all heat transfer. Both useful and usable energy are gone, leaving...nothing. And we all (think we) know that nothing is a state of existence just begging to be everything.

The heat death of the universe (aka ultimate entropy) is the best of the best arguments as to why human immortality would really suck.

In fact, living through the heat death of the universe (provided you had a habitat where you would not experience the unimaginable torture of living in a vacuum) would be enough to drive any person clinically insane, and then some.

On the other hand, it would be a pretty sweet pick-up line.

"Hey baby, the universe is gonna end in 100 billion years, wanna come back to my place while we still have the chance?"
Heat Death Of The Universe © 1988 by Pamela Zoline.

A really, really trippy tale of a housewife named Sarah Boyle who's very smart and completely unravels. She's obsessed with entropy, Heat Death Of The Universe, numbers, lists, and science generally. The story is about 6 pages long, and is divided into numerical sections, as such:

20. Sarah Boyle pours out a Coke from the refrigerator and lights a cigarette. The coldness and sweetness of the thick brown liquid make her throat ache and her teeth sting briefly, sweet juice of my youth, her eyes glass with the carbonation, she thinks of the Heat Death of the Universe. A logarithmic of those late summer days, endless as the Irish serpent twisting through jeweled manuscripts forever, tail in mouth, the heat pressing bloating, doing violence. The Los Angeles sky becomes so filled and bleached with detritus that it loses all colour and silvers like a mirror, reflecting back the fricasseeing earth. Everything becoming warmer and warmer, each particle of matter becoming more agitated, more excited until the bonds shatter, the glues fail, the deodorants lose their seals. She imagines the whole of New York City melting like a Dali into a great chocolate mass, a great soup, the Great Soup of New York.

In the Boyle house there are four clocks; three watches (one a Mickey Mouse watch which does not work); two calendars and two engagement books; three rulers, a yard stick; a measuring cup; a set of red plastic measuring spoons which includes a tablespoon, a teaspoon, a one-half teaspoon, one-fourth teaspoon and one-eighth teaspoon; an egg timer; an oral thermometer and a rectal thermometer; a Boy Scout compass; a barometer in the shape of a house, in and out of which an old woman and an old man chase each other forever without fulfillment; a bathroom scale; an infant scale; a tape measure which can be pulled out of a stuffed felt strawberry; a wall on which the children's heights are marked; a metronome.
It's really quite good. Yummy stuff.

Other info:
ISBN: 0914232894
Copied without permission, in the interest of promoting her work. I can't find very much information about her, really, I discovered her through an English course. If anyone can provide more info, please do.
No! The universe started with a Big Bang and will not end in a cold, dead whimper!

Astronomers now believe that the expansion of the universe is increasing. They call the cause zero-point energy or Einstein's cosmological constant, or dark energy. It's not well understood, but they assume it will continue this way, always accelerating. So, it's natural to think that our universe will get colder and colder until everything stops moving.

We're not that lucky! There's an idea by Robert Caldwell and his colleagues Marc Kamionkowski and Nevin Weinberg called 'The Big Rip', and it seems much more likely.

To understand this, consider that there's an edge to the universe. It's not an edge like a waterfall. It's called the 'observable universe'- at a certain distance away the expansion of space gets so fast relative to say, the Earth, that not even light can make it from there to the Earth- the space in between is expanding so fast that the distance increases by more than 299,792.458km per second, the speed of light, so the light never makes it.

Now, as the expansion speeds up, the closest distance for the expansion to exceed the speed of light goes down, so the distance to the edge of the observable universe goes down. For all intents and purposes, your personal bit, the bit of the universe that can effect you is shrinking; as the growth rate goes up. So, accelerating expansion leads to a smaller universe! Ironic huh?

Now, the universe is pretty big- at the moment.

But as the expansion rate increases, the size gets ever smaller. Eventually it will be smaller than the distance to the nearest stars, and they would disappear from the Earths point of view, ripped away by the expansion rate of the space. Then smaller than the distance to the Sun, so the Earth gets very dark and is no longer in orbit, because gravity travels at the speed of light and the Earth and Sun are moving apart very, very fast.

But the electromagnetic forces that hold physical objects like the Earth, and you, and me, together travel at the speed of light too. So, a few weeks later, the Earth will just fall apart without any hope of keeping it together, ripped by the ever accelerating expansion. Then the people, then cells, then the the molecules, then atoms fall apart, then the subatomic particle size is reached.

What happens after that, is anyones guess. But we certainly won't be there to find out...

Thirteen billion years you've got and that's it!

"Oh well, just time for a quick bath then; pass the sponge someone!" - Douglas Adams

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