# I will answer any physics questions you have for your Sci Books here



## Odanata (Jan 27, 2022)

Hi, i am new to the forum. and in order to help contribute, I will answer any physics questions authors have for their Sci Fi books. I have a background in mathematical physics a good understanding of General relativity and Quantum Mechanics, as well as Classical phyics


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## petergrimes (Jan 27, 2022)

Hi Odanata,

nice to meet you, that's a really kind offer which I know will be very helpful to many. I have quite a few that I will need help with in future as i progress with one of my stories, so I will most certainly be stopping by. Cheers mate, I'll be popping back sometime later this year, most likely to ask a few things about dark matter and quantum entanglement. Thanks for the offer. All the best PG


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## Odanata (Jan 27, 2022)

petergrimes said:


> Hi Odanata,
> 
> nice to meet you, that's a really kind offer which I know will be very helpful to many. I have quite a few that I will need help with in future as i progress with one of my stories, so I will most certainly be stopping by. Cheers mate, I'll be popping back sometime later this year, most likely to ask a few things about dark matter and quantum entanglement. Thanks for the offer. All the best PG


No problem happy to help


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## Bloggsworth (Jan 27, 2022)

My physics question is: why is it impossible to cut a straight cut in cheddar cheese with a knife?


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## NajaNoir (Jan 28, 2022)

I want to hide something very big in the ocean, about the size of Madagascar. How can I make such a thing visible to only a select few who know its exact location?
I don't fully understand bending the light to make something invisible can you give me the layman's rundown?


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## Non Serviam (Jan 28, 2022)

Oh good, delighted to meet you!

The plot of my intended story involves a corporation bringing asteroid 1943 Anteros into an Earth-Moon trojan point.  Minimum orbit intersection distance is 9,337,900km on 24 May 2127.  If my corporation moves it as efficiently as possible by way of low-energy transfer, what's the delta-v budget and how long does the journey take?


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## Odanata (Jan 28, 2022)

NajaNoir said:


> I want to hide something very big in the ocean, about the size of Madagascar. How can I make such a thing visible to only a select few who know its exact location?
> I don't fully understand bending the light to make something invisible can you give me the layman's rundown?


Interesting, well light literally changes direction when passing from one substance to another, this is called refraction. The refractive index of sea water is 1.38. Whether or not your island was visible under the water would depend on where your observer was, for instance if your observer is directly above the island they will see it as the light will not be bent. However if someone looks out at a small angle of inclination to the surface of the water they are unlikely to see the island, dependin* on how deep the island is under the water.

If you wanted to hide-something that large from a plane overhead for instance the best bet would be to cover it in some sort of tarp that mimics the light given off by the ocean beneath it. Not sure if that helps.


NajaNoir said:


> I want to hide something very big in the ocean, about the size of Madagascar. How can I make such a thing visible to only a select few who know its exact location?
> I don't fully understand bending the light to make something invisible can you give me the layman's rundown?


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## Odanata (Jan 28, 2022)

Non Serviam said:


> Oh good, delighted to meet you!
> 
> The plot of my intended story involves a corporation bringing asteroid 1943 Anteros into an Earth-Moon trojan point.  Minimum orbit intersection distance is 9,337,900km on 24 May 2127.  If my corporation moves it as efficiently as possible by way of low-energy transfer, what's the delta-v budget and how long does the journey take?


Sorry, I can’t help with this. There is quite a bit of calculation involved. You might need a nasa scientist to work that out for you. I can offer plausibility advice, rather than work out answers to problems, those days are over for me


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## epimetheus (Jan 28, 2022)

Kind offer. With regards to orbital mechanics would it be possible to set up an Earth-moon cycler in a similar manner to Buzz Aldrin's idea for an Earth-Mars cycler?


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## Odanata (Jan 28, 2022)

Odanata said:


> Interesting, well light literally changes direction when passing from one substance to another, this is called refraction. The refractive index of sea water is 1.38. Whether or not your island was visible under the water would depend on where your observer was, for instance if your observer is directly above the island they will see it as the light will not be bent. However if someone looks out at a small angle of inclination to the surface of the water they are unlikely to see the island, dependin* on how deep the island is under the water.
> 
> If you wanted to hide-something that large from a plane overhead for instance the best bet would be to cover it in some sort of tarp that mimics the light given off by the ocean beneath it. Not sure if that helps.


Or of course have it deep under water where no one can see it. Anything over 1000 meters would not give off any light


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## Odanata (Jan 28, 2022)

epimetheus said:


> Kind offer. With regards to orbital mechanics would it be possible to set up an Earth-moon cycler in a similar manner to Buzz Aldrin's idea for


Yeap, 





						Lunar cycler - Wikipedia
					







					en.m.wikipedia.org


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## Kent_Jacobs (Jan 28, 2022)

Nice idea. I nearly suggested this the other day in you introduction thread.


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## NajaNoir (Jan 29, 2022)

Odanata said:


> Interesting, well light literally changes direction when passing from one substance to another, this is called refraction. The refractive index of sea water is 1.38. Whether or not your island was visible under the water would depend on where your observer was, for instance if your observer is directly above the island they will see it as the light will not be bent. However if someone looks out at a small angle of inclination to the surface of the water they are unlikely to see the island, dependin* on how deep the island is under the water.
> 
> If you wanted to hide-something that large from a plane overhead for instance the best bet would be to cover it in some sort of tarp that mimics the light given off by the ocean beneath it. Not sure if that helps.



That helps a lot,  thank you so much.


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## Omits (Jan 30, 2022)

Odanata said:


> Hi, i am new to the forum. and in order to help contribute, I will answer any physics questions authors have for their Sci Fi books. I have a background in mathematical physics a good understanding of General relativity and Quantum Mechanics, as well as Classical phyics


I have Aliens arrived. Clearly they are advanced well beyond our physics. I have their craft able to travel at enormous speeds (150Km/hr) in atmosphere and have a gravity generator on board which is independent of the Earths gravity so e.g. can float. The Human abducted to represent the Aliens has to try to explain some idea about how the tech works but does not understand it fully (of course). Any ideas how he should try to explain to a scientific audience (if at all)?


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## epimetheus (Jan 31, 2022)

Odanata said:


> Yeap,
> 
> 
> 
> ...



Thanks. Some pretty complicated orbits there. Do you happen to know, or know any resources, that describe how these orbits traverse the Van Allen belts?


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## Odanata (Jan 31, 2022)

Omits said:


> I have Aliens arrived. Clearly they are advanced well beyond our physics. I have their craft able to travel at enormous speeds (150Km/hr) in atmosphere and have a gravity generator on board which is independent of the Earths gravity so e.g. can float. The Human abducted to represent the Aliens has to try to explain some idea about how the tech works but does not understand it fully (of course). Any ideas how he should try to explain to a scientific audience (if at all)?


Hi, You May have made a mistake with the speed, 150km/hr is as fast as a stat card car can go. There are four known forces in the universe at the moment ( although there is some talk about a fifth at cosmic scales) the dynamics of these four forces are all well understood. The two forces that are relevant above the quantum level are gravity, and electromagnetism. Gravity is always an attractive force, and is a very weak force for small masses. Gravity can’t be artificially generated without a large mass, the larger the mass the stronger the force of gravity, like a black hole for instance. You can think of very heavy masses as bending space and time ( general relativity).
For your purposes it is more likely that some sort of electromagnetism could be used to hover objects, magnetic forces are repulsive, and electromagnetism can generate these forces.


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## Phil Istine (Jan 31, 2022)

What a wonderful thread.
I'm tempted to ask if washing machines contain miniature black holes from which single socks cannot escape, or is it simply that I can't see them because light is unable to leave,

Something I struggle to get my head around is that an individual object cannot exceed light speed but it's said that the universe expands faster than light speed 186,000 miles or 300,000km per second).


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## Lawless (Feb 1, 2022)

Phil Istine said:


> an individual object cannot exceed light speed


Right. Is it because both time and space are discrete rather than continuous? I'd like an expert's comment on that.


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## Phil Istine (Feb 2, 2022)

Lawless said:


> Right. Is it because both time and space are discrete rather than continuous? I'd like an expert's comment on that.


I'm no expert but I think e=mc^2 (energy equals mass times the speed of light squared) is the key, where the greater the mass, the more energy is required to propel it.

From that we might conclude that if the energy is constant, a smaller mass will be able to travel faster.

When we have photons (i.e. light), they are said to be massless. I'm unclear whether this means that zero energy can propel them or whether a miniscule amount of energy is required. e=mc^2 implies e/m=c^2. As m=0, this would normally be regarded as a mathematical (division by zero) error, but it looks like the key as to why light speed is a universal speed limit.

If we assume this speed limit is correct, could the expansion of the universe by faster than light speed be tenuous proof of the existence of antimatter i.e. m having a minus sign in front of it?

Anyway, the above assumes e=mc^2 is correct, and I question whether that is the right place to start.

As you can see, my knowledge on this is sparse. I'd love to spend a few weeks with Brian Cox in a bid to gain more insight.


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## Non Serviam (Feb 2, 2022)

Lawless said:


> Right. Is it because both time and space are discrete rather than continuous? I'd like an expert's comment on that.



Energy and matter seem to come in _quanta_, which we think are indivisible packages -- things like photons, electrons and quarks that can't be split.     But time seems to be a continuum, or at least: we have never found a quantum of time, and we have no reason to think one exists.

The universe doesn't have one rate of expansion.  Most galaxies are moving away from us and some are moving away from us faster than the speed of light, but there are galaxies moving towards us, such as the Andromeda Galaxy which will, a very long time in the future, crash into the Milky Way.


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## Odanata (Feb 4, 2022)

Phil Istine said:


> What a wonderful thread.
> I'm tempted to ask if washing machines contain miniature black holes from which single socks cannot escape, or is it simply that I can't see them because light is unable to leave,
> 
> Something I struggle to get my head around is that an individual object cannot exceed light speed but it's said that the universe expands faster than light speed 186,000 miles or 300,000km per second).


Some say that socks are entangled, but frequently one entangled sock falls through spontaneously created Einstein Rosen bridges(wormholes), there is likely a mouth of a primordial wormhole spewing out socks for 100 of light years somewhere on the others side of the galaxy. There is unfortunately no evidence for this theory yet however.

More seriously, light travels through space, and in space it travels with a fixed velocity. The universe on a large scale is expanding, not in space. But the actual space in the universe is expanding, so parts of the universe can move away from each other faster than the speed of light without anything ever going faster than the speed of light. 

Interestingly this is what causes the redshift of light into the infrared that the James web telescope is being sent into space to observe. As the space that light has travelled through has been stretched, increasing the wavelength of that light, so that it can only be observed in the infrared.


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## Odanata (Feb 4, 2022)

Lawless said:


> Right. Is it because both time and space are discrete rather than continuous? I'd like an expert's comment on that.


There is a minimum length both in time and space, called plank length and plank time. Below these times and lengths equations break down.


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## Odanata (Feb 4, 2022)

Odanata said:


> There is a minimum length both in time and space, called plank length and plank time. Below these times and lengths equations break down.


Planck after Max Planck, to give the great scientist his due


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## Lawless (Feb 4, 2022)

Odanata said:


> There is a minimum length both in time and space


I was not asking whether or not that is so. I knew it already. I asked if that is the reason why nothing can move faster than the speed of light.


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## Odanata (Feb 4, 2022)

Phil Istine said:


> I'm no expert but I think e=mc^2 (energy equals mass times the speed of light squared) is the key, where the greater the mass, the more energy is required to propel it.
> 
> From that we might conclude that if the energy is constant, a smaller mass will be able to travel faster.
> 
> ...


E = mc^2 tells you that energy and mass can be converted. C is the speed of light, and is a very big number, so c squared is a huge number, that tells you that for a tin6 bit of mass you can get a huge amount of energy, this is how the sun works, and how nuclear energy works. This is an outcome of Einstein’s special theory of relativity. 
All massless particles move at the speed of light, what you are describing above is what’s known as lorentz contractions or time dilation, there is a factor known as the Lorentz factor ( which is quiet simple) that tells you how time dilates at speed, and how mass dilates, and how length dilates. It’s worth having a look I will post a link to it underneath.


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## Odanata (Feb 4, 2022)

Odanata said:


> E = mc^2 tells you that energy and mass can be converted. C is the speed of light, and is a very big number, so c squared is a huge number, that tells you that for a tin6 bit of mass you can get a huge amount of energy, this is how the sun works, and how nuclear energy works. This is an outcome of Einstein’s special theory of relativity.
> All massless particles move at the speed of light, what you are describing above is what’s known as lorentz contractions or time dilation, there is a factor known as the Lorentz factor ( which is quiet simple) that tells you how time dilates at speed, and how mass dilates, and how length dilates. It’s worth having a look I will post a link to it underneath.











						Length contraction - Wikipedia
					







					en.m.wikipedia.org


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## Odanata (Feb 4, 2022)

Lawless said:


> I was not asking whether or not that is so. I knew it already. I asked if that is the reason why nothing can move faster than the speed of light.


I would say not, a thought experiment that is worth having is considering the possibility that there were no limit to speed of light. Then some information could travel across the universe in no time, we would be able to see the whole universe as it is now at the same time. 
What Einstein did when coming up with the speed of light was a paradigm shift, similar to when Copernicus proposed the helio centric model for the solar system. 
The ideas of space and time are mental constructs to help us model the universe, and up until Einstein blended the two they were incorrectly held mental constructs. Space and time would have a lot less meaning if we didn’t need to perceive things in those terms to model the universe.


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## NajaNoir (Feb 7, 2022)

Hello!

I want to rip open spacetime, create a hole in the sky wide enough to drop/throw an enormous amount of stuff.  A dimension tear? wormhole, not sure what to call that, but it is meant to connect two worlds. Would there be a (likely) moment of silence underneath said hole? I'm wondering what it might sound like, was told that it is likely (no one knows for sure) all sound would disappear? Thoughts?

Thanks!


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