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Physics, Astronomy & Cosmology / Re: If you throw a mouse or elephant at someone in space, which will move them more?

« on: 07/01/2020 21:59:58 »

What is the cutoff mass for [projectile returning to first person]?  This is not the same mass as the answer to my post 12 question.

I don't know how to calculate that without using trial and error. You likely use calculus

It's actually just complicated algebra, but I did my reply-12 thing by guessing, and hit it in my 2nd guess, the first guess being 50kg. I had a hunch and it turned out to be correct. This is the case of the 2nd guy returning the projectile with the same energy as the first throw, not at the energy of the incoming projectile.

One more thing on a different but related issue. If I wanted to write a snooker simulation but with variable-mass balls and with the angles of impacts leading to the balls going off at different angles, can the same maths as above still be used just by breaking things down into vectors?

Snooker is complicated.  It isn't frictionless balls in a vacuum, which is actually pretty easy arithmetic.  Snooker has to deal with table friction, especially immediately after the impacts where the balls are moving at a different rate than their spin.  That spin deflects both balls from their initial trajectories, and I'm not up to the challenge of computing the angular inertias and funny spins with non-horizontal axes.

Yes, it's quite easy to do with frictionless balls in space.  Target ball moves directly away from its impact point and incoming ball is deflected in a way that preserves momentum and energy.

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Physics, Astronomy & Cosmology / Re: If you throw a mouse or elephant at someone in space, which will move them more?

« on: 05/01/2020 01:55:25 »

I'm still trying to find out how you work out how fast the two objects will move apart for a fixed amount of input energy.

I started with the elephant which is posited to mass 10x myself.  So I chose a speed for myself that was 10x the elephant speed, or 1 and 0.1 m/sec respectively.  This is an arbitrary speed but not an arbitrary ratio.  Then I computed the energy (1/2mv²) for each.  50 + 5 totals 55 joules, so that's the energy of the spring that would impart those speeds on those two objects.
Then I had to do the same with the mouse, but starting with a known energy this time, and I got 0.104 and 10.4 m/sec for myself and the mouse respectively, a ratio of 100 this time.  It still adds up to 55 joules.

If spring efficiency wasn't an issue, you could simply divide the total energy equally between both objects.

You can't do that.  The elephant gets a 10th the energy that you do when you throw it.  The mouse gets 100x the energy when you throw it.  Energy can only be divided equally when an equal mass (the wife) gets thrown.
Momentum gets divided equally.  Both total momentum and energy is preserved on the throwing event.  The former is preserved upon catching event and the energy is lost to friction (or possibly captured if the friend has a smaller spring).

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Physics, Astronomy & Cosmology / Re: Can Atoms Touch Each Other?

« on: 18/12/2019 18:21:13 »

Atoms (in molecules say) keep each other at a distance to the the repulsion of their electron clouds.
For electrons to literally 'touch', they'd have to be at the same location, and the EM repulsion force (not to mention the even stronger nuclear forces) would repel at pretty much infinite force. Things can get arbitrarily close, but to touch they'd have to be at the same location, which the forces don't allow.

Hence the definition of 'touch' typically being more reasonable than that, as chiralSPO points out.  Atoms are considered to be touching if their repulsion due to their electrons makes a significant contribution to the distance between the atoms.

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Physiology & Medicine / Re: Is your perception of colours the same as mine?

« on: 16/12/2019 19:53:45 »

Dearest Peeps Of Klevur Knowing Stuff,

Peeps with peepers is more like it.

How do I know that my eyes perceive colours exactly the same as yours ?  For all i know your orange might be my green ?

You don't.  No way to compare subjective experience, but there are some people that see more colour than typical, sort of the opposite of being colour blind.  They see patterns in flowers that might appear white to me.  They get offended that the crayon box never seems to be anywhere near complete.

Squirrels see yellow.  Humans do not, and the banana appears the same colour as an object that emits only red and green light.  Squirrels could tell the two apart effortlessly, not because they see better, but because they see actual yellow.

Do both eyes see colours exactly the same  ?

I think one would notice if otherwise, so barring health issues, yes.

Does the colour of eyes have any effect on colour perception ?

No

Will I still perceive colours the same when I'm 80 like i do now ?

Again, barring health issues, yes.  I've had cataracts, so my world sort of faded to foggy white.  My colours were not off, but I needed 3cm high font to read anything.  All fixed now.  My mother lost most of here colour vision and was amazed when it was restored.  All the vivid hues and such that she'd forgotten about.

*What's your favourite colour ? (US translation service: "colour" = "color" sheesh !!)

Boring if there's only one.  The prior owners of my house liked gold.  All the drapes, carpets, hardware, and even the cars.  Sheesh indeed...

Why do we prefer certain colours over another ?

I don't, so don't know.

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General Science / Re: Can I turn Pixie into a diamond?

« on: 16/12/2019 14:38:31 »

Your Pixie seems to have walked through (and face-planted in) a shallow dish of bleach.
Nevertheless, she has proven her abilities by prevailing over her leopard-trainee foe in the corner there.

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General Science / Re: Can I turn Pixie into a diamond?

« on: 16/12/2019 13:55:24 »

My childhood cat had the same name.  Thing was all hair, making it sort of a challenge to find the cat within.

That said, she was regularly threatened with being made into either a toilet rug or a tennis racquet, but never a diamond.  I suppose that being a carbon based life form, one could isolate the carbon and then squeeze it into a diamond, but it takes warm hands.

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General Science / Re: Can fire cast a shadow?

« on: 16/12/2019 13:49:45 »

Fire very much does block some light as it consists of glowing particles in part.  Other light gets deflected by the heat, but that effect will not produce a crisp shadow.

So put a spotlight to the side of a fire and it will indeed cast a shadow on a wall on the opposite side.

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Physics, Astronomy & Cosmology / Re: What Do You Call A Moon Of A Moon ?

« on: 16/12/2019 03:05:30 »

Does this then mean that the Sun is a moon of Sagittarius A ?

Few stars actually orbit Sgr-A.  The sun is not one of them as its orbital speed is far too large at this distance from such a small object.  No, we go around the galaxy in a non-elliptical path and if we orbit anything, it is the general cloud of assorted objects and (mostly) dark matter that exists mostly (but not entirely) within the radius of our circuit.  Sgr-A is only a tiny percentage of this mass, and is thus just one of those assorted objects.

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General Science / Re: When do YOU die in a many worlds interpretation?

« on: 10/12/2019 14:13:16 »

On the subject of superposition ... do waves/particles in a superposition have mass?

All particles have mass.  Things that move at light speed have relativistic mass, but not proper mass.  Waves are not really 'things', but rather disturbances in a medium, and any mass associated with them is best associated with the medium and not the disturbance.  Superposition makes no difference to any of this.  A cat in superposition of being dead and alive still masses one cat, else I could make an infinite energy device using the concept.

I ask because ... A wave or A particle with mass would have some affect on the actual surrounding space. And if these waves/particle were in a superposition wouldn't the effect on the surrounding space be greater?

No, the same.

In my head I see a fish in a bath with the consequence of displacement and water disturbance. If there were many more fish in the bath I would expect to see more displacement and water displacement.

Yes, but there is only the one fish, yes?  If it is in some kind of superposition, that's fine, but it cannot displace more water.

Entering the bathroom and observing the one fish the water level would be lower than before I entered the room.

You've envisioning two fish, rather than one in a superposition of states (like facing north and facing south).  The water has measured the direction the fish is facing, so the water is entangled with the fish (is in superposition along with the fish).  It takes an incredible amount of effort to not measure this and collapse the superposition state.  Not being in the room isn't anywhere near enough, but they have actually done it with a macroscopic object (one large enough to see without instruments).

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Physics, Astronomy & Cosmology / Re: WIll the rogue waves from the sun affect auroras?

« on: 07/12/2019 22:13:51 »

Nasa's Parker Solar probe is recording some strange sun activity. WIll the 'rogue' characteristics of this activity affect the aurora?

The activity is 'strange' in that this is the first data sent back from a probe exploring places never before measured.  The probe seems to have measured these 'rogue [plasma] waves' on its first passes through the atmosphere, indicating that these waves are quite commonplace, just not ever measured before.  As such I'd think it not likely to affect aurora as would more exceptional activity such as would be measurable directly from Earth as opposed to only this local probe.

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General Science / Re: When do YOU die in a many worlds interpretation?

« on: 07/12/2019 13:41:57 »

It's strays from my original question but do you think it is possible, in the world of quantum mechanics for instance, to get a firm grasp on the facts of the matters in question without a mathematical foundation?

Well, I do happen to have a reasonable mathematical background, but I certainly cannot follow much of the mathematics of either quantum or relativity theories posted in the various papers. That doesn't stop me from accepting or trying to understand the conclusions of those that can.

So I happen to know relativity fairly well, and I know many of the differences (if not the deep details) of the various quantum interpretations, all of which are essentially philosophy, not science, since they lack any empirical test to distinguish them.

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General Science / Re: When do YOU die in a many worlds interpretation?

« on: 07/12/2019 03:13:09 »

As B-C says, MWI does not support the concept of identity of objects, be they living or not.
I have all the respect in the world for Tegmark, but he's got an incompatible preferred-world dualist attitude in his description of this quantum suicide machine.  The two views are not compatible.

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Physics, Astronomy & Cosmology / Re: A reported object travelling faster than the speed of light?

« on: 26/11/2019 17:42:25 »

I saw on space.com they reported an object travelling faster than light, apparently it was a star that had been ejected, how is this possible? Doesn't the mass of the object become massive according to general relativity?

Never heard of anything getting shot out at super speed and still managing to remain intact enough to be classified as a star.
Perhaps https://www.space.com/41724-neutron-star-merger-superfast-jet.html
Headline:
"Faster Than Light? Neutron-Star Merger Shot Out a Jet with Seemingly Impossible Speed"

But it goes on to correct itself: "In the 155 days between two observations, the jet appeared to move 2 light-years, a distance that would require it to travel four times faster than light. This "superluminal motion" is an illusion created as the jet is pointed nearly toward the Earth; it is actually moving at about 97 percent light speed."

Not sure how it being pointed nearly at us makes it look like it's going faster. You'd think that would make it appear slower.  I saw a meteor come straight at me, and it didn't appear fast at all. In fact it looked stationary, getting brighter and then winking out.

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Physiology & Medicine / Re: how can microscale vessels be actually made?

« on: 18/11/2019 18:24:27 »

Many structures can be made with similar techniques to manufacture of computer chips where the materials are laid down, or trenches dug using light and masks.  It's sort of a 3D printer where atoms are added or removed at a slow rate similar to crystal formation.

As for filling them, I have no idea.  I cannot see how a container might carry acoustic waves.  More reasonable is that the waves are generated from outside and focused on a particular point and the containers (which just float by randomly) will break/open at the place where the acoustic waves are focused and thus deliver their cargo to precise locations.

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Physics, Astronomy & Cosmology / Re: Do things stop decaying in space?

« on: 10/11/2019 05:23:45 »

So if an astronaut  left the space station and couldnt get back, or anyone's body was just let go in space would it freeze and stay like that for ever? Would it move or stay in one place?

Being in a suit means you're under pressure, so the body might suffer a similar fate as one on Earth at a similar temperature, in an enclosed container.  Space isn't particularly cold or hot as there is no matter to give it temperature, so the eventual temperature of the body in the suit will depend on how much time it spends in the sun or shade.

As for where it will go, a body let go outside a space station will drift nearby it for quite a while, orbiting in its own path not much different than the station. It would take considerable energy to actually push a human outside of Earth's gravity well. If it orbits near the space station, the orbit will probably decay over a long time and then fall to Earth, just like the space station will if not pushed now and then.

It would move, yes.  There is always mass (like Earth or the sun, or whatever) accelerating every object.  Nothing that is stationary (in some frame) can remain so for any length of time. I can thing of zero examples of a non-accelerating object. If an object (body?) was near a space station, but somehow stationary relative to Earth, it would immediately just fall to Earth.

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Physics, Astronomy & Cosmology / Re: Do things stop decaying in space?

« on: 09/11/2019 22:38:44 »

I heard someone today saying, when talking about Voyageur 2, that it would go on travelling in space for billions of years. This suggests that it will never break down/'decay,change. is this true of anything that gets into space?

All particles have a half-life of sorts, but given what space probes are made of, it is not of any real concern. Billions of years doesn't begin to touch that.

Shorter term, the probes are continuously bombarded with bits of matter it runs into, solar rays, and all the same sorts of things that make life inhospitable to humans (breaks us down similarly).  That sort of thing will age the probes faster than the decay of its materials, and it will always be surrounded by material since it has nowhere near the speed needed to exit the galaxy.

Our galaxy is scheduled for being eaten by our neighbor in the next 5-15 billion years (swallowing takes a while), and this process has the potential to fling either Voyager or our sun in some random direction, into the void or into the thick of it where the bombardment is greater.

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Physics, Astronomy & Cosmology / Re: Can you help me understand "speed"?

« on: 09/11/2019 13:31:40 »

Quoted from latest episode "eggs, eyes etc..., in answer to the question: "How fast a rocket can humans safely travel in?"
"So the Earth rotates at 600 miles an hour.

Maybe where they are (Montreal?). At the equator, it is over 1000 mph.  25000 mile circumference in 24 hours, no?

So we're currently on the earth going 600 miles an hour, because we're on the earth we're also going 600 miles an hour.

We're going 600 mph relative to the center of Earth.  Speed is always relative, so not specifying the relation is wrong.  I'm not moving 600 mph relative to my mailbox. I'm nearly stationary relative to that.

The Earth is speeding around the sun at 70,000 miles per hour. So we are also speeding around the sun at 70,000 miles an hour. The sun is speeding through the galaxy at 450,000 miles an hour, which means we're also spinning at 450,000 miles an hour."

Just so, relative to the sun and the galaxy respectively.

I'm probably dim, but how can I understand "speed" in this statement? Are the references always implicit? For example, in the first statement "we're on earth going 600 mph", should I implicitly understand that the "reference" (if that's even the correct word!) is the centre of the earth, and this jumps to the sun in the second statement "The Earth is speeding around the sun at 70,000 miles per hour". In other words, in astronomy, when speeds are mentioned, should I just assume that I should understand the quoted speed relative to an "obvious" reference.

You got it.  Speed is always relative to something, and language usually lets you get away with letting it be implicit, but the reference is always there.  The speedometer on my car shows speed relative to the road under it, and doesn't bother to say that explicitly.
Velocity (a vector) is also a relation.  So I might be moving at speed 600 mph relative to Earth, and some guy on the planet opposite me also is moving at the same 600 mph speed, but our velocity is very different since we're moving in different directions.  Speed is a scalar, and velocity is a vector.

The reason I'm asking the question is because I simply don't "get" relativity, time dilation etc...e.g. in the classic example of my "twin" charging off in a rocket at near the speed of light aging differently to me, am I not simply "aging" at the same rate relative to my twin, because relative to him/her, I'm charging off in the opposite direction at an equal and opposite speed, therefore cancelling out any warping of time?

Under relativity, it is the other twin that is moving relative to either twin, so in the current inertial frame of either twin, the other twin is aging slower.  Not intuitive, but that's how it works.
When the 'travelling' twin turns around, his inertial frame changes, and in that frame the twin back home simultaneous with the turnaround event is much older than his age in the outbound frame.  That's the relativity of simultaneity in action, and is why one twin is older than the other when they finally meet again.

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Physics, Astronomy & Cosmology / Re: Does information have mass?

« on: 08/11/2019 20:23:07 »

Information has entropy associated with it.
Changing information changes the entropy, and this requires energy.
...
See: https://en.wikipedia.org/wiki/Entropy_in_thermodynamics_and_information_theory#Negentropy

To expand on this, according to the linked page, the energy is not the mass of the information, but the minimum energy required to save/change a bit of information.  Hence a blank terabyte thumb drive (or say one with the first half set to 0 bits and remainder 1) masses the same as the same thumb drive crammed with a library of findings.  But it takes this minimum energy (and creates the resulting entropy) to change it from one state to the other.

In my simplistic understanding: If some object carries information, it carries energy; this energy has an equivalent mass, and an associated gravitational field.

I don't see how this follows from the linked page, but any object has mass, and mass has energy, so it indeed stands that energy is required to store information in an object.  But it doesn't follow that an object with information masses more than the same object without information (all else being equal). That's a thin statement since a blank thumb drive still has a big consecutive swath of 0's, which is arguably information.

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Physics, Astronomy & Cosmology / Re: Does information have mass?

« on: 08/11/2019 18:46:17 »

I read about entangled atoms/electrons transferring information across vast distances ‘instantaneously’ or ‘near-instantaneously’. I also read that the speed of this information transfer was 'around 3-trillion meters per second – or four orders of magnitude faster than light.                   ( https://futurism.com/chinese-physicists-measure-speed-of-quantum-entanglement-2)

There is no evidence of actual information transfer with entanglement scenarios.  If there was, it would not have a finite speed (a mere 4 orders of magnitude) as this pop-science article suggests.  Certain interpretations of quantum mechanics posit such information transfer, and also transfer of information arbitrarily far into the past, but without a falsification test, such interpretations cannot be verified.
So the rule of thumb is: If you can't send a message with it, it isn't information transfer, and hence no faster than light information transfer has ever been demonstrated.

My understanding is that anything with mass cannot travel at or beyond the speed of light.

Not even things without proper mass can, according to any theory that holds to the principle of locality.  Said interpretations mentioned above of course must deny this principle.

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Physics, Astronomy & Cosmology / Re: What happens when both slits are observed by in the double slit experiment?

« on: 07/11/2019 23:12:06 »

Relativity is a classical and deterministic theory. Quantum mechanics introduces probability, which is not deterministic.

I don't think relativity theory says anything about determinism one way or the other.

QM theory also doesn't say. It just says that the outcome of an experiment cannot be predicted regardless of how much information of the system can be measured ahead of time.
There are interpretations that are hard indeterministic (fundamental randomness), soft deterministic (randomness is phenomenally emergent, but not fundamental), and hard deterministic (there is only one possible future which could be computed if all variables were known).