Calculating the end of our universe.

Could this be done by working out the density of black holes, how fast they are growing, moving etc

I would have thought we could work out a reasonable approximation by using the number of known black holes their average mass and how often they occur in mapped space and extrapolating outwards from there?

Thoughts from the physicists?

a reply to: johnb

Why do you think black holes have anything to do with the end of the universe? Black holes are completely marginal compared to the other forces ruling our universe.

The current hypothesis is that the universe will keep expanding forever, hence it has no end, only a slow heath death.

a reply to: Develo

I know that is the current view but if nothing can escape the gravitational pull of a black hole, then surely by definition at some distant point in the future, the black holes will have swallowed everything including each other till there is only 1 mega black hole containing the whole universe.

I wonder if like everything else in nature the universe is cyclical - everything ends up in one black hole which then explodes causing a big bang - rinse and repeat

a reply to: johnb

Black holes only swallow what is inside their event horizon.

Everything else is simply orbiting around them or out of their reach.


Also how do you know the universe isn't infinite in size? No one knows.

i my opinion the end of the universe will happen when i draw my last breath, be it tomorrow or 70 years from now.
But that's just my way of looking at things

a reply to: johnb
No I don't think black holes will ever swallow everything. For one thing, black holes will evaporate through Hawking radiation if that exists, and the size for the black holes which will evaporate will continue to increase as the universe cools. Currently the critical mass for a black hole to evaporate is somewhere around the mass of the moon.

Black Holes

If Hawking's theory of black hole radiation is correct, then black holes are expected to shrink and evaporate over time because they lose mass by the emission of photons and other particles.[32] The temperature of this thermal spectrum (Hawking temperature) is proportional to the surface gravity of the black hole, which, for a Schwarzschild black hole, is inversely proportional to the mass. Hence, large black holes emit less radiation than small black holes.[86]

A stellar black hole of 1 M☉ has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrink. To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole needs to have less mass than the Moon. Such a black hole would have a diameter of less than a tenth of a millimeter.

As the 2.7K temperature of the CMB continues to cool, more massive black holes will evaporate. So that addresses black holes.

We have to be careful about speculating about the end of the universe, as in 1998, some new observations changed our view of the death of the universe. With new data I suppose that could happen again. With that in mind the current speculation is a heat death called the "Big Freeze":

Big Freeze

Observations suggest that the expansion of the universe will continue forever. If so, the Universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario is popularly called the Big Freeze.

a reply to: Develo

from NASA black hole q&a

doga_lover54: Do black holes expand and grow?

Jerry: We've found at least a dozen solar mass black holes in our own galaxy. There are probably millions of supermassive black holes at the centers of other galaxies but so far we've only seen a few of the nearest of these.

Akarsh_Valsan: Can black holes really suck things up?

Jerry: At a distance, black holes really don't have more gravity than normal objects, so at a distance they really won't suck things in any more than a normal object of the same mass.

So as the black hole grows so does the event horizon presumably??

a reply to: Arbitrageur

Yes if this turns out to be true and black holes do dissipate over time then my idea would be false

Jerry: Good question. The enormous gravity of a black hole would Doppler-shift any radiation that comes from or near the edge of a black hole, including gamma rays.

sciencejunkie57: Is there any evidence that black holes emit any major amounts of Hawking Radiation?

Jerry: No -- Hawking Radiation is still controversial and hasn't been directly observed.

a reply to: johnb

by definition at some distant point in the future, the black holes will have swallowed everything including each other till there is only 1 mega black hole containing the whole universe.

What about when they collide?
Asteroids collide, do suns and black holes?

Have we witnessed this?

"extrapolating" "our universe"

and I wonder someTImes why anImals don'T Talk. fascInaTIng. absoluTely fascInaTIng. who needs a Telescope when I could sImply read abouT "exTrapolaTIng" "our unIverse".
I am abouT To go look for a squirrel and say ThaT To see whaT happens. hopeful. really hopeful.

a reply to: intrptr

Jerry: At a large distance from black holes, there really are no effects except for its gravity. This is interesting because, for example, if the sun were a black hole instead of a normal star, we would hardly see its effects because we'd only feel the same amount of gravity and nothing else from the black hole.

tonster: How are we able to detect gravitational waves that are created from two black hole collisions. Wouldn't the waves be pulled into the black hole like light?

Jerry: When two black hole collide (they actually don't collide, but circle each other until they coalesce) enormous "gravity waves" are thought to be emitted. One ground-based system specifically developed to detect these gravity wave is called LIGO. It's a long, laser-based interferometer system. Details of this system can be found by Googling "LIGO." NASA is planning a much larger space-based version of LIGO called LISA. You may also want to Google "LISA NASA."

a reply to: johnb

Jerry: When two black hole collide (they actually don't collide, but circle each other until they coalesce) enormous "gravity waves" are thought to be emitted.

Thanks, I read that. My question was have they witnessed this? So much about singularities is theorized.

Jerry: It's impossible to see inside of a black hole.

originally posted by: johnb
a reply to: Develo

from NASA black hole q&a

doga_lover54: Do black holes expand and grow?

Jerry: We've found at least a dozen solar mass black holes in our own galaxy. There are probably millions of supermassive black holes at the centers of other galaxies but so far we've only seen a few of the nearest of these.

Akarsh_Valsan: Can black holes really suck things up?

Jerry: At a distance, black holes really don't have more gravity than normal objects, so at a distance they really won't suck things in any more than a normal object of the same mass.

So as the black hole grows so does the event horizon presumably??

Yes but it is still completely marginal.

The quote explains clearly black holes aren't really that different from other normal stellar objects, gravitation speaking. The ratio of stars / black holes clearly shows that stars have infinitely more impact on the shape of our universes than black holes;

a reply to: intrptr

I don't know but would doubt it - as i would imagine something so huge would take years/centuries..... to happen.

a reply to: Develo

I understand what you are saying

What i am trying to provide as a counterpoint argument is that as it/they grow so does their effect, so the more mass they attain over time so their gravitational pull and the size of their event horizon grows proportionally.

So surely over billions/trillions of years they would merge and grow so massive there would be nothing else left apart from one giant black hole containing everything.

a reply to: johnb

And I understand what you are saying too. It's just you greatly overestimate the attraction force of black holes.

The universe is expanding meaning things are getting away from black holes, not closer.

Black holes will never attract more mass than just what's in their close vicinity.


I know you are trying to play devil's advocate for your theory, but it simply doesn't work the way you imagine it.

a reply to: johnb

So surely over billions/trillions of years they would merge and grow so massive there would be nothing else left apart from one giant black hole containing everything.

I get what you are asking. My counter to that is (if) the Universe is boundless (infinite) then that can never happen.

Galaxy Clusters bear out part of your theory though. Gravitationally speaking Galaxies are massive black holes orbiting each other on a time line so long that we can't visualize it.

Galaxies do 'collide', too.

I mages

a reply to: Develo

I think i understand now

As the universe is continually expanding the matter of the universe will be out of range of the black holes 'pull'.

I can see the logic of that, however if the black holes are moving and growing in mass all the time and presumably new ones are being continuously formed throughout the universe is it not possible that eventually they would consume everything?

P.S. I can see that if they didn't move they would eventually fade as they would have nothing left to absorb.

originally posted by: johnb
I can see the logic of that, however if the black holes are moving and growing in mass all the time and presumably new ones are being continuously formed throughout the universe is it not possible that eventually they would consume everything?

I don't know about everything, but they will become dominant until they evaporate, but since you asked about the end of our universe, I think they will probably evaporate in the end and will just be a "phase" on the way to the end:

Future of an expanding universe

Black Hole Era

10^40 years to 10^100 years

After 10^40 years, black holes will dominate the Universe. They will slowly evaporate via Hawking radiation. A black hole with a mass of around 1 M☉ will vanish in around 2×10^66 years. As the lifetime of a black hole is proportional to the cube of its mass, more massive black holes take longer to decay. A supermassive black hole with a mass of 10^11 (100 billion) M☉ will evaporate in around 2×10^99 years.

Hawking radiation has a thermal spectrum. During most of a black hole's lifetime, the radiation has a low temperature and is mainly in the form of massless particles such as photons and hypothetical gravitons. As the black hole's mass decreases, its temperature increases, becoming comparable to the Sun's by the time the black hole mass has decreased to 10^19 kilograms. The hole then provides a temporary source of light during the general darkness of the Black Hole Era. During the last stages of its evaporation, a black hole will emit not only massless particles but also heavier particles such as electrons, positrons, protons and antiprotons.

If protons do not decay as described above

In the event the proton does not decay as described above, the Degenerate Era will last longer, and will overlap the Black Hole Era. In a timescale of approximately 10^65 years, apparently rigid objects such as rocks will be able to rearrange their atoms and molecules via quantum tunnelling, behaving as a liquid does, but more slowly. However, the proton is still expected to decay, for example via processes involving virtual black holes, or other higher-order processes, with a half-life of under 10^200 years. For example, under the Standard Model, groups of 2 or more nucleons are theoretically unstable because chiral anomaly allows processes that change baryon number by a multiple of 3.

Dark Era and Photon Age

From 10^100 years

The lonely photon is now king of the universe as the last of the supermassive black holes evaporates.

After all the black holes have evaporated (and after all the ordinary matter made of protons has disintegrated, if protons are unstable), the Universe will be nearly empty. Photons, neutrinos, electrons, and positrons will fly from place to place, hardly ever encountering each other.

Depends on what you mean by end of the universe...

End of human life?
End of all life?
End of matter?
End of time?