For large blackholes of course. And this actually makes other interesting property. Our universe is in fact giant blackhole with our own event horizon outside it. This also support cyclic big bang theory. Once entire universe will collapse to singularity, the smallest possible particles shatters, leaving pure energy. Pure energy doesnt have "static" mass so no gravity => kaboom, we have new iteration. Theory of multiverse (multiple black holes aka universes) is out of scope here because we will never be able to escape ours.

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raattgift 8 hours ago | parent | next [-]

The observables in our sky do not match any interior metric for a black hole. In particular generically black hole metrics concentrate a central mass, and (from a Raychaudhuri equation perspective) the known sources of shears and pressures that work against this concentration are insufficiently strong to block ever greater collapse. Additionally, shears and pressures enter into the stress-energy tensor. That's why the centre of a BH can be a singularity.

Observations of distant galaxies and the cosmic microwave background do match the (expanding vacuum) Lemaître-Robertson-Walker metric with the distribution of matter-density described by the Friedmann equations. Distant galaxies fill the sky and are receding from us, from our perspective; they are not concentrating in any sort of middle.

There is insufficient evidence to conclude that a big crunch is in our future.

"Pure energy" is represented in the stress-energy tensor just fine. General relativity's Einstein Field Equations exactly relates the stress-energy tensor to the curvature of spacetime. It gravitates, your argument just falls down.

<https://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor#/...>

	▲	itsamario 2 hours ago \| parent \| next [-]
		Science mapped out our solar system and developed base12 to account for rotation and orbit. What I haven't found is an accounting of our solar system's patterns in our galaxy. We know about axial precession but we don't know the official cause and some suspect it's related to a pull from another galaxy or a swayish wobble from our solar system's rotation in the galaxy. Same for a supposed magnetic flip in the earths core. They might be related but we seemingly only know of the precession measured as 1 degree per 72 years but the magnetic north pole doesn't align with any noted patterns nor cause.
	▲	thunderbong 7 hours ago \| parent \| prev [-]
		Thank you for your comment. I've heard the parent argument earlier as well. I wasn't aware of these points.

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adrianN 10 hours ago | parent | prev | next [-]

It is my understanding that energy produces a gravitational field regardless of the form it takes.

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Maxatar 5 hours ago | parent [-]

That's correct, in fact almost nothing Borg3 has said is remotely accurate.

One cool thought expressed by Penrose is the possibility that all matter will eventually decay or annihilate and all that's left will be massless radiation such as photons. If this happens then the concept of space and time itself will cease since from within the reference frame of a photon space and time are undefined.

In this scenario the distinction between an infinitely expanded, cold, and dilute universe and an extremely small, hot, and dense universe becomes undifferentiable. Without any physical scale by which to distinguish the two, the far distant future of our universe where all matter has disappeared can be equivalently viewed as the big bang of a new universe.

This is what Penrose calls conformal cyclic cosmology [1]. There was a time when physicists debated whether the universe would continue expanding forever or whether gravity would eventually halt its expansion and cause it to collapse back in on itself in a Big Crunch, potentially giving rise to another Big Bang. Conformal cyclic cosmology allows for an endless repeating cycle of universes even in the case where the universe expands forever, by identifying the infinitely distant future of one universe with the Big Bang of the next.

This is highly speculative and almost certainly false, but it's at least grounded in actual physics and is kind of poetic.

[1] https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

	▲	sandworm101 4 hours ago \| parent [-]
		>> all matter will eventually decay or annihilate and all that's left will be massless radiation such as photons. If this happens then the concept of space and time itself will cease since from within the reference frame of a photon space and time are undefined. So all matter is pushed out (dark energy) eventually reaching its own event horizon in the dimension we call time, then continues as photons (Hawking radiation). And eventually after all the matter has done so, everything collapses and this universe ends? Sounds like we are in an aging BH to me.

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nkrisc 10 hours ago | parent | prev [-]

What is “pure” energy?

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ButlerianJihad 9 hours ago | parent | next [-]

It is the subtitle of a #3 synth-pop hit by Information Society, which debuted only 16 months before the release of the unrelated Belgian techno anthem, "Pump Up the Jam".

	▲	aceazzameen 7 minutes ago \| parent [-]
		This gave me a good laugh. Mostly because that's exactly what went through my head when I read the original post at top.

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Borg3 8 hours ago | parent | prev [-]

Photons? They cannot be stopped, because they have no "static" mass? As far as they move, they react to gravity, not sure if they can provide its own gravity field. Might be a case as far as they move. Not expert here :)

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raattgift 8 hours ago | parent | next [-]

Photons have momentum. They can drive solar sails. They can kick electrons out of atomic orbitals. Lots of them streaming outwards hold up the outer layers of stars, keeping them from collapsing. Radiation pressure.

Momentum-density is represented in the stress-energy tensor, and so is directly related to spacetime curvature. Light feels and generates gravity.

A sibling comment points out the hypothetical kugelblitz as an extreme example. In cosmology textbooks you can read about the "radiation-dominated era" of the first roughly 50000 years of the universe where the energy density working strongest against the expansion was dense photons (and neutrinos).

	▲	jjtheblunt 2 hours ago \| parent [-]
		I had a radiometer when i was a kid ... is that momentum what makes it spin, because i thought the light was heating the black surfaces more than the white surfaces, so the air molecules bounced more vigorously away from the black. i didn't think about photons having momentum when i was 8, though. https://a.co/d/00nIWNpB

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pavel_lishin 8 hours ago | parent | prev [-]

Apparently, they can: https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)