Recent content by Ray Gunn

In my opinion, this is analogous to the cyclical universe idea, but from a more interesting, and possibly more meaningful perspective. Instead of an endless cycle of big bangs and crunches with no clear beginning, we start from a point where the universe has no measurable size, and the expansion...

Be glad you didn't choose Austin. The forecast, according to space and weather expert Eric Berger, is for heavy cloud cover with possible thunderstorms. We're locked-in with our plans; too late to change them. Wishing you better luck!

I bet none of the Ax-3 crew were upset by the weather-induced departure delay. Congrats on getting some extra free time in space.

Not mentioned in this article but another reason for a likely delay of Artemis 2 beyond 2024 is continued study and resolution of issues with the Orion heat shield which experienced greater ablation than expected.

Currently it's thought that an asteroid 1-km or larger hits the Earth on average every 650,000 years. The new study, if correct, suggests this size asteroid hits the Earth somewhat more often, on average every 250,000 years. That's a risk of 1:25,000 per century, or roughly a human lifetime...

Note from my original question that I'm referring to a measurement of the object's orbital velocity or period as it would appear to an observer "far away" from the black hole. From other comments, the velocity or period would appear slower. And thus to correctly calculate the black hole's mass...

Given that an object in a stable close orbit just outside the event horizon of a black hole will experience time dilation; then to a distant observer, will the orbital period appear to be slower than expected by purely Newtonian mechanics?

Given an object in a stable close just outside the event horizon of a black hole. To a distant observer, will time dilation make the orbital period appear to be longer/slower than expected by purely Newtonian mechanics?

According to quantum theory, when not observed, particles such as electrons and positrons exist not at precise points in space but rather as spread-out "clouds" of probable positions. And yet, an electron and positron will collide and annihilate as if they exist as discrete point-like...

Why doesn't an outside observer measure the mass of a black hole as being located at the event horizon (instead of the center) due to time dilation. I imagine light passing close to a black hole would bend differently depending on whether the mass is at the center versus at the event horizon...

It seems ironic that we talk of terraforming Mars when we can't seem to prevent or counter climate change on Earth, which should be orders of magnitude easier.

The "mirror-image universe" mentioned in the recent blog on parallel universes is identical to an idea I wrote about roughly a decade ago in replies to various physics blogs such as Sean Carroll's Cosmic Variance. In addition to what was written here, I suggested this could possibly explain what...

Conventional Wisdom suggests that the entire mass of a Black Hole lies within an infinitely small, infinitely dense Singularity at the center. But an alternative hypothesis is that the Black Hole's mass lies at the Event Horizon. It seems to me that this could be tested by observing the light...

To an outside observer, matter falling into a Black Hole will appear to slow to a stop at the Event Horizon due to time dilation. Why then are we able to observe -- via gravitational waves -- the collision and merger of two black holes into a single larger Black Hole, i.e. why doesn't it appear...