Gravastars and black holes, a weird cosmic double act

Showing all posts tagged: Albert Einstein

Gravastars and black holes, a weird cosmic double act

2 January 2025

The concept of gravastars (or gravitational vacuum stars) is a fascinating alternative to the idea of black holes, although if their presence were ever proved, they would not rule out the existence of black holes. Proposed by Pawel O. Mazur and Emil Mottola some twenty years ago, these objects are consistent with Albert Einstein’s general theory of relativity.

Gravastars, like black holes, form in the aftermath of some supernova explosions. They are relatively small, their size might be similar to London, capital of the United Kingdom.

In terms of appearance they are black, and a little like balloons, having an extremely thin shell, consisting of matter scientists do not yet understand. Their interior is filled with a vacuum, or dark energy, bustling to break out, but unable to do so. Gravastars sound like an incredible phenomena, but in a universe some think is devoid of dark energy, I wonder if they could actually be present.

Time, not dark energy, may be causing the universe to expand

27 December 2024

Dark energy does not exist, and the universe, while continuing to expand, is not doing so in a uniform fashion. In other words, the cosmos may look more like a potato, rather than a sphere. This according to recent research by astronomers and scientists at the University of Canterbury (UC), based in Christchurch, New Zealand.

As if that’s not startling enough, things become truly mind boggling when we look at the nature of time in a universe that may be devoid of dark energy. Time, you see, is moving at different speeds, depending on the location. Within our galaxy, the Milky Way, a clock ticks more slowly than one that might be situated elsewhere in an empty region of the universe, say the mid-point between our galaxy and the Andromeda galaxy, which is two and a half million light years distant.

The model suggests that a clock in the Milky Way would be about 35 percent slower than the same one at an average position in large cosmic voids, meaning billions more years would have passed in voids. This would in turn allow more expansion of space, making it seem like the expansion is getting faster when such vast empty voids grow to dominate the universe.

Because there is more gravity inside a galaxy than outside, clocks will be slower. This is a concept called gravitational time dilation, which Albert Einstein predicted when he published the theories of special relativity and general relativity, early in the twentieth century. Differences in clock speeds may not be surprising then, but the UC research illustrates just how stark these variations might be.

Albert Einstein, special relativity, and an afterlife: this is heavy

22 July 2023

planet and galaxy, image/montage by Lumina Obscura

Image courtesy of Lumina Obscura.

Is your dead grandmother… still alive? The answer is…

… yes…

… in a sense.

That’s if information in the cosmos is never destroyed, but rather… rearranged. In this case the information I refer to are the atoms, sub-atomic particles, and who knows what else, that make up everything in the universe, including us, and our predeceased family members.

Interaction with this information, which over eons diffuses into the cosmos after our deaths, may then be possible if cosmic consciousnesses, being ours — somehow — come into being one day, and are able to envelope the universe, and eventually encounter your late grandmother’s information.

This is the understanding I took away from this Big Think video featuring German theoretical physicist Sabine Hossenfelder, which I saw on Open Culture. Best you watch for yourself though, and see what you make of it, as matters of maths and physics are not my thing. Otherwise, some fodder for a little contemplative thinking this weekend, perhaps?