Recent comments in /f/askscience

jimb2 t1_ja2onlm wrote

Reply to When the Andromeda and Milky Way galaxies combine; will the super black holes in both galaxies eventually combine because of gravitational pull? by TrumpedUpStupidity

In Newtonian physics, two bodies can orbit each other forever. It's stable. They exert gravitational pull on each other but gravity is frictionless so no energy and momentum is lost and it continues forever.

In general relativity, two orbiting bodies will produce gravitational waves that propagated some energy and momentum away. This is a tiny effect in "normal" situations so it would take eons for enough momentum to be lost for the black holes to coalesce. If the black holes do get close together and hit relativistic speeds then the radiated gravitational energy can become enormous and really drop the black holes into each other fast, as in the detected gravitational wave events. This is the last few wild seconds of a process that may have taken billions of years to develop.

However, a real galaxy is not actually a two body problem. The black holes will be interacting with lots of other stars in the combined galaxy. In these interactions, the smaller bodies (stars) tend to gain momentum and can even be flicked right out of the galaxy. The larger black holes will lose momentum and slow down. These effects are sometimes called gravitational "friction". Over many interactions, the black holes will lose sufficient momentum to fall into each other. By this time they will have either absorbed most of stars or flicked them out into intergalactic space, never to be seen again.

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xratedcheese t1_ja2jlru wrote

Reply to Can you experience g-force without acceleration? by tenminutes101010

Their claim:

"Giant Rider is capable of punching out 1.5G acceleration while the competition can only deliver 0.5G acceleration! "

That "punching out" was certainly carefully chosen. For a very brief period (fraction of a second?) they could jerk the whole cabin to give you the feeling of actual acceleration for that brief time, but absolutely not the feeling of sustained acceleration unless they are suspending the cabins and whirling them up to speed like amusement park swings.

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2xOPisANidiot t1_ja2hji7 wrote

Reply to comment by Psychocumbandit in How old is the ISS REALLY? by gwplayer1

>would not that effect be zeroed out by a corresponding segment of the orbit when it is moving back towards the earth based observer at the same relatavistic speed?

Direction is irrelevant for time dilation. High speeds always means slower time, never faster.

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RunObjective1970 t1_ja2bxvz wrote

Reply to Is the H5N1 bird flu just a variation of the common flu virus? by The_Mayor_of_Reddit_

There are already a few vaccines which can be made to work, and some others already being made.

So far the cases in Cambodia do not look as though they are spreading from person to person, but who knows, the news is so new that only time will tell. These events have happened in the past, and all of the infected people were working with birds, or living at the homes of people who do, which is so far the only way these rare events happen. If it does start to spread among humans, from person to person, it will be easier to contain as flu viruses are not nearly as contagious as Sars Cov 2. Flu is not really air borne, its droplet spread. There are also quite a few vaccines already made and ready for use.

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mfb- t1_ja2bm7b wrote

Reply to comment by ArcherofFire in Water on Earth is not Constant. Why ? by ItsDivyamGupta

Oxygen isn't a relevant process (although technically possible: Nitrogen-15 + neutron can become nitrogen-16 which decays to oxygen-16), but carbon is: Nitrogen-14 + neutron -> carbon-14 + proton. That's the dominant way carbon-14 is produced. It decays back to nitrogen over thousands of years, and we use that process for radiocarbon dating.

/u/Minnakht /u/ArcherofFire

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