Random Science Facts Thread!

[ProtoJeb21]

Black holes can kill you...with LIGHT. I'm not talking about radiation from the debris disk, but from the black hole itself. It's called Hawking Radiation, a form of black-body radiation caused by a complex interaction between particles and antiparticles at the edge of the event horizon. This slowly evaporates the black hole, and the less massive the BH is, the quicker it will evaporate before exploding into pure gamma rays. While Hawking Radiation gives out only feeble amounts of visible light, it can produce incredibly energetic forms of gamma rays and heat the black hole to temperature equivalent to the primordial universe mere seconds after the Big Bang. I'll be doing a more in-depth analysis on it later, but for black holes with masses around that of a Star Destroyer or aircraft carrier...the effects are absolutely horrifying. Less extreme are black holes that produce 99% of their radiation in the form of UV light. They would be about as massive as the Death Star (5e+16 kg) and have a temperature close to 3 BILLION degrees Fahrenheit. Due to their high temperatures, small size, and incredibly long lifespan (1e+32 years) they could easily cancer-ify everything within a few tens of light years. And believe it or not, there are even more horrifying black holes than this. 

[ChrisSpace]

Fun fact: If a spacecraft left Earth and landed on the asteroid Apophis exactly six months before it flies past Earth in 2029, it would only take about 2 meters per second of Dv, or about 122GJ of kinetic energy and 23.2kN of thrust for a 2-month burn, to change the asteroid's path to impact Earth. Redirecting 153814 2001 WN5 with the same time limit would take roughly 15.8m/s of Dv, or about 34-705TJ of energy and 0.82-17MN of thrust for a 2-month burn.

Edited November 5, 2017 by ChrisSpace

[insert_name]

There are more microbes in your body than there are human cells

[magnemoe]

On 31.10.2017 at 11:38 AM, Green Baron said:

There is no clear sign of intraspecies violence among humans before the end of the palaeolithic.

(The few unclear ones can easily be explained with taphonomy, accidents, ritual buryings or simply misinterpretations)

It was an group who was found killed in Kenya who looked like they had been massacred. 
http://www.cam.ac.uk/research/news/evidence-of-a-prehistoric-massacre-extends-the-history-of-warfare
This might be the start period you talk about. 

Else it was probably very rare. Chances of getting killed by an human is very low anyway, humans are very peaceful animals, we are good at large scale organisation and this includes warfare. 
But numbers of humans killed in wars over other reasons is very low, and hunter gatherers can not do large scale stuff well. 

And yes hunting accidents was probably the most common reason for human getting killing humans back then the same way traffic accidents is now. So finding some with an spear wound in chest was probably an hunting accident. 

[Camacha]

23 hours ago, CastleKSide said:

We still do not know how bicycles stay upright. The standard explanations involve gyroscopic stabilization, however scientists have build bikes with extra counter rotating wheels to cancel this effect and they still work.

I think a fairly recent bit of research found it has to do with the steering geometry and taking advantage of where a bike tends to fall when getting off-balance. There seems to be a consensus that gyroscopic stabilization is far too weak to account for how bikes behave.

It's like the persistent fable that air over a wing has to move faster because of its longer trajectory. There is nothing that dictates fluids (like air) should to this and the actual mechanism is a bit more complicated. Yet everyone seems to think air molecules agree upon meeting each other at the same time behind the wing.

Edited November 3, 2017 by Camacha

[mikegarrison]

41 minutes ago, Camacha said:

I think a fairly recent bit of research found it has to do with the steering geometry and taking advantage of where a bike tends to fall when getting off-balance. There seems to be a consensus that gyroscopic stabilization is far too weak to account for how bikes behave.

Yes, this is true, but it's certainly not "recent research". This has been understood by bike designers since pretty much forever.

The key geometry is what is shown on that picture as "trail". The bigger the trail is, the more stable the bike will be, but that also makes the steering heavy.

Cars self-steer for much the same reason, though the mechanism works slightly differently.

Edited November 3, 2017 by mikegarrison

[Ultimate Steve]

4 hours ago, ChrisSpace said:

Fun fact: If a spacecraft left Earth and landed on the asteroid Apophis exactly six months before it flies past Earth in 2029, it would only take about 2 meters per second of Dv, or about 122GJ of kinetic energy, to change the asteroid's path to impact Earth. Redirecting 153814 2001 WN5 with the same time limit would take roughly 15.8m/s of Dv, or about 34-705TJ of energy.

Cue supervillain theme music...

[Green Baron]

8 hours ago, magnemoe said:

It was an group who was found killed in Kenya who looked like they had been massacred. 
http://www.cam.ac.uk/research/news/evidence-of-a-prehistoric-massacre-extends-the-history-of-warfare
This might be the start period you talk about.

Not palaeolithic ;-)

There are a few other cases ... might be interesting to look at what happened to human subsistence at that time.

Edited November 3, 2017 by Green Baron

[Green Baron]

5 hours ago, Ultimate Steve said:

Cue supervillain theme music...

You might just have written the plot for the next Bond or so ...

[Green Baron]

A report on the state of US climate research and climate change:

https://science2017.globalchange.gov/downloads/CSSR2017_FullReport.pdf

If someone is interested, browse through it, there is a lot of information in it, but it is a national report, not all the work is included and it is geographically biased (of course :-)) and overall rather conservative.

Edited November 4, 2017 by Green Baron

[ChrisSpace]

On 3 November 2017 at 2:22 PM, Ultimate Steve said:

Cue supervillain theme music...

If you want a more supervillain-ey target, redirecting Swift-Tuttle to impact Earth in 2126 with a Dv change in 2060 (roughly half an orbit beforehand) would take 11m/s of Dv, or an energy equivalent to nearly 90 megatons of TNT and over 360MN of thrust for a 6-year burn. If your time limit and energy budget are halfway between these two extremes, redirecting 4179 Toutatis to impact Earth in 2069 with a Dv change 2 years earlier would require a bit over 47m/s of Dv, or an energy equivalent to a bit over 13 megatons of TNT, or over 150MN for a 6-month burn.

As for what propulsion system to use for this, unless you can get a working very-high-thrust antimatter or fusion engine, I'd personally recommend either chemical or nuclear-pulse propulsion.

Edited November 30, 2017 by ChrisSpace

[NSEP]

[Grand Ship Builder]

The universe is theorized to expand faster than light.

[magnemoe]

On 3.11.2017 at 2:45 AM, mikegarrison said:

Yes, this is true, but it's certainly not "recent research". This has been understood by bike designers since pretty much forever.

The key geometry is what is shown on that picture as "trail". The bigger the trail is, the more stable the bike will be, but that also makes the steering heavy.

Cars self-steer for much the same reason, though the mechanism works slightly differently.

the trail will make the front wheel want to point forward, the question is why an bicycle is stable at speed, obvious one is gyro from wheels but that effect is to weak.
Don't think the trail explains it unless its an feedback effect with it. 

[Scotius]

Cells in a human brain can make more conections between themselves than there is atoms in observable universe.

Drunk ants will always fall on their left side.

They also hear with their legs.

A grasshopper sitting on the ground in Europe can feel an earthquake in Japan.

Honey doesn't spoil. Ever. You can safely eat honey that was enclosed in tombs by ancient Egyptians.

You can die of malnutrition while eating copious amounts of rabbit meat.

Jumping flea accelerates at... 1500 m\s squared. But only over a very short distance because of atmospheric drag.

[Grand Ship Builder]

1 hour ago, Scotius said:

Drunk ants will always fall on their left side.

That's about right.

[Camacha]

On 03/11/2017 at 2:45 AM, mikegarrison said:

Yes, this is true, but it's certainly not "recent research". This has been understood by bike designers since pretty much forever.

The key geometry is what is shown on that picture as "trail". The bigger the trail is, the more stable the bike will be, but that also makes the steering heavy.

Cars self-steer for much the same reason, though the mechanism works slightly differently.

You're talking about the trail effect, which is what causes shopping cart wheels to align with the direction of travel. Researchers have done mathematical analysis on the forces involved and found a third phenomena, other than gyroscopic forces and the trail effect, which seems to work through the distribution of mass. It's strong enough to keep a bike upright on its own, which is proven by a model they built that self corrects without the other two phenomena influencing the model.

The research looks to a little over five years old, which is recent enough. You can read all about it here.

[Camacha]

10 hours ago, NSEP said:

I've heard that one before, but there's a problem with that. It assumes active high binary logic. Active high means that a bit is represented by a signal going high, like going from 0 volt to 5 volt. However, because that's just a convention, it's not how all of the data is encoded. Many chips are actually active low, which means a bit is encoded by a signal going from high to low, like going from 3.3 volt to 0. In that case, more data means less electrons. Another major problem would be magnetic hard drives, which don't encode with voltages or charges at all. Instead, a hard drive encodes information by the direction of the magnetic domains on a surface, which means it shouldn't change weight with the adding or removing of data. Most of Earth's data resides on magnetic hard drives - by far.

Even though it makes for a great story and isn't based on fiction, it's also not quite accurate.

[mikegarrison]

4 hours ago, magnemoe said:

the trail will make the front wheel want to point forward, the question is why an bicycle is stable at speed, obvious one is gyro from wheels but that effect is to weak.
Don't think the trail explains it unless its an feedback effect with it. 

Gyroscopic force is much too weak. It's even too weak for motorcycles, whose wheels move faster and are a lot heavier.

When the bike starts to lean, the trail on the wheel causes the bike to turn, which creates an inertial force that counters the lean. The slower the bike is moving, the harder it has to turn to create enough inertial counter-force. When moving too slowly, it can't do it and falls over. This is why bikes are more stable the faster they are moving.

2 hours ago, Camacha said:

You're talking about the trail effect, which is what causes shopping cart wheels to align with the direction of travel. Researchers have done mathematical analysis on the forces involved and found a third phenomena, other than gyroscopic forces and the trail effect, which seems to work through the distribution of mass. It's strong enough to keep a bike upright on its own, which is proven by a model they built that self corrects without the other two phenomena influencing the model.

The research looks to a little over five years old, which is recent enough. You can read all about it here.

Notice that they had to build something that looks entirely unlike a bicycle in order to generate their effect, and even in the article you quoted they admit normal bikes can be made unstable by reducing trail.

[Green Baron]

"Ozone hole" apparently as small as almost 40 years ago:

https://earthobservatory.nasa.gov/IOTD/view.php?id=91212&eocn=home&eoci=iotd_title

Could the Montreal protocol of 1989 have a positive effect ?

Edited November 5, 2017 by Green Baron

[mikegarrison]

7 hours ago, Green Baron said:

"Ozone hole" apparently as small as almost 40 years ago:

https://earthobservatory.nasa.gov/IOTD/view.php?id=91212&eocn=home&eoci=iotd_title

Could the Montreal protocol of 1989 have a positive effect ?

Yes, I think the Montreal Protocol shows that we can clean up after ourselves, if we get serious enough about it. Unfortunately, CFCs are measured in parts per trillion, while man-made CO2 is more than 100 parts per million. So the scale of the problem is much more immense for CO2.

There is still no drop-in replacement for halon in terms of aircraft fire suppression. So far, airplanes have been getting by with halon that was stockpiled before the Montreal Protocol came into effect, supplemented with halon recovered from decommissioned firebottles. There are some who would like to get an exemption from the Montreal Protocol to make more halon for this limited purpose.

Edited November 5, 2017 by mikegarrison

[Green Baron]

I am sceptic concerning CO2 emissions. Some countries apparently dream about falling back into a steam age while others work on fusion technology. Btw., random science ... err ... "fact", i read an interview with one of the scientists of Wendelstein 7X, where he said that we might expect a working fuison reactor in the second half of this century. Reading tea leaves :-)

Provided one of the currently researched technologies Tokamak, (e.g. Iter) or the above Stellarator proves in the next 2 decades that it can hold a plasma long enough.

Maybe before someone flies to Mars ?

Edited November 5, 2017 by Green Baron

[DAL59]

It takes 1.44 km/s of delta-vee to land on Europa from a low orbit.

It takes 150m/s to escape Ceres from a low orbit.  

I have a delta vee map as my screen background.  

Edited November 5, 2017 by DAL59

[p1t1o]

Can you observe/extract information from a 100% non-radiating object without bouncing anything off it? Without bouncing photons or electrons or anything off it? Without touching it or using fields of any kind, no EM radiation, electric or magnetic fields? Without dumping energy into or extracting energy from the object, in any way?

Yes.

Information can be extracted from an object using only probability, statistics and quantum weirdness. It is enough that the possibility exists, that a photon could impact an object and reveal its presence/properties, the photon never has to touch it for the possibility alone to affect the results of the probe.

https://en.wikipedia.org/wiki/Elitzur–Vaidman_bomb_tester

It is a real effect that has been physically observed.

Edited November 5, 2017 by p1t1o

[Grand Ship Builder]

In the scale of the Universe, we are in the very middle. It takes just as much Planck lengths to reach the length of a human brain cell, as it takes brain cells to reach the length of the Observable Universe.