Considering the movie Interstellar, I just did not understand how solving the equation saved the earth from the Blight. As I understood, the equation had to do with gravity. What was the relation of gravity with a massive infestation of a microorganism?
121925
In Interstellar, there is a Blight destroying all the world's crops.  If Plan A involves launching a space colony, presumably full of crops, etc., how could they avoid bringing the Blight with them?     At the end of the film we see that they've actually created space colonies.  How did they manage to launch and populate them without bringing the Blight with them?
58300
How to solve this question? Also it would be great if someone could tell me from which book this question is from?
36052
In the movie Interstellar, is the time dilation the team suffers on the water planet Miller caused by the proximity of the planet to Gargantua or by the planet's gravitational pull?  In the beginning I thought it was caused by the black hole, but later I was reading  and the guys said it was caused by the planet. Do we have some information about this?
97077
This is a sci-fi story set on Earth. From the depths of space comes these microbes that latch onto electromagnetic fields. Anything electronic is rendered useless. There's the usual stuff where governments try to solve the issue but make it ultimately worse. It's only when they realise that the microbes surround the planet that they realise it is futile. The story closes with people having returned to a simpler life, using medieval farming methods, not using electricity in any form, getting about by horse, etc. I think it was a short story.
59457
F = gravitational force between the earth and the moon,  G = Universal gravitational constant = 6.67 x 10^(-11) Nm^2/(kg)^2,  m = mass of the moon = 7.36 × 10^(22) kg  M = mass of the earth = 5.9742 × 10^(24) and  r = distance between the earth and the moon = 384,402 km   F = 6.67 x 10^(-11) * (7.36 × 10^(22) * 5.9742 × 10^(24) / (384,402 )^2  F = 1.985 x 10^(26) N   The above all i took from    Age of Moon 4.53 billion years (From google)  So Earth has been producing a force of 1.985 x 10^(26) N for 4.53 billion years I do not know how to calculate the total energy spent so far(Please some one do the favor) from force and time but it must be very huge. if E = mc^2 then atleast some of the mass of earth must have disappeared in producing this energy or where did the energy come from ?   Somewhere some one has answered if we place a ball above earth then during that time we did the work and when it fell down to the earth that work changed into kinetic energy ok accepted but the moon is being pulled towards earth for unlimited time where does the earth get the energy from to do so ?  @Emilio Pisanty Thanks for your reply.  "it needs to move the object in the direction that the force acts in"  Even though the force applied by earth is perpendicular to the direction of motion the moon's direction is definitely changed because of the force applied by the earth and the moon is moving a little towards earth from the straight line otherwise the motion would be a straight line. If earth did no work on moon why would the moon not go in straight line escaping earth's gravity. Even if we accept that earth does no work and spends no energy in making the moon orbit around it,By newton's law any body which accelerates needs force and since the moon keeps accelerating all the time(changing its direction of movement)where does moon gets this force continuously for such a long time.
110059
Sci-fi novel I read as a kid, with a house and a caretaker. The house was used by alien races as a station when travelling through space. The house looked normal from a distance but could not be entered because of some invisible force field. The man was chosen by the aliens as a caretaker of this house.
98557
How does a   outside a galaxy help to explain a ?  Suppose for simplicity we use a model of a star rotating about a more massive star in a fixed circular orbit. For another star at larger radius, the velocity should be smaller but observationally for spiral galaxies, the opposite happens (moves at even more speed or at least at the same speed as the closer star).  People hypothesize that dark matter halo may be present “surrounding” the system (i.e., halo exists outside the system) to account for such observation. I feel that exactly the opposite should be the case that is, dark matter halo should be inside the galaxy rather than outside. Reason being, if dark matter is outside the galaxy then the effective gravitational pull on the rotating star towards the center will be reduced due to outward attraction on the star exerted by dark matter existing outside. Thus, its speed of rotation should be reduced; but we observe the opposite. So how does dark matter halo "surrounding" a galaxy help to explain galaxy rotation curve? Where am I making mistake in argument?
45959
Trying to recall a short story I read decades ago. As best I recall, in an desperate effort to defeat humanity in a war they are losing, aliens send piloted bombs back in time to destroy the Earth before life has started. Miscalculation causes destruction of planet into asteroid belt and creates conditions for life on Earth.  The story was from perspective of a genetically engineered pilot of the bomb as it flew back in time to its suicidal goal.   I think the title was simply 'T' - the name of the pilot of the bomb - but trying to search internet for a title like that is not working out too well. Even tried 'shortest title for a story'.
17632
There is something I don't understand about the  $H$, as it seems to clump two concepts together that I can't quite unify in my head. On the one side, we have  $$V = D H$$  which means that for a given distance $D$, there is a certain amount of new space created over time - and $H$ is simply the factor that makes this relationship work. So, for example, say we have two points 1 Mpc apart, this would mean they recede at about 70 km/s away from each other  (given our current approximation of $H$).  Now the thing I can't wrap my head around is that   $$T =\frac{1}{ H}$$  is also the age of the universe. Contrary to claims made on, say, Wikipedia this means that $H$ cannot possibly have been a constant throughout the past 13 billion years, because mathematically $1/H$ means that $H$ must be continually shrinking as the universe ages.  So if $H$ did start out as some huge value and is now shrinking over time, doesn't this mean the expansion of the universe is slowing down? Because if $H$ is shrinking, I'll get a lower value of $V$ today than I'll get tomorrow. Shouldn't the notation then be more like  $$V = DH(t)$$  So which one is it? If $1/H$ is simply the solution for $D=0$, how can we use it as the expansion-velocity-per-unit-of-distance at the same time? What's worse, how can literature say $H$ has probably been more or less constant forever and simultaneously assert that $1/H$ is the current age of the universe? What am I missing?
54549
Hello,  in the picture there is an equation I can not understand. What I do not understand is how to get to the first step. I have been thinking and thinking but can not find an explanation. Could somebody please explain? Thanks.
31579
The gravitational force on your body, called your weight, pushes you down onto the floor. $$W=mg$$ So, what is the weight equation through general relativity?
119309
Trying to teach myself general relativity. I sort of understand the derivation of the geodesic equation $$\frac{d^{2}x^{\alpha}}{d\tau^{2}}+\Gamma_{\gamma\beta}^{\alpha}\frac{dx^{\beta}}{d\tau}\frac{dx^{\gamma}}{d\tau}=0.$$ which describes  "how" objects move through spacetime. But I've no idea "why" they move along geodesics.   Is this similar to asking why Newton's first law works? I seem to remember reading Richard Feynman saying no one knows why this is, so maybe that's the answer to my geodesic question?
70006
We all know $a = \frac{\mathrm{d}v}{\mathrm{d}t}$. A little application of the chain rule leads to the relation $$a=v\frac{\mathrm{d}v}{\mathrm{d}x}$$ But the above equation shows that $a=0$ whenever $v=0$. And this must be wrong, as when we throw something vertically from the earth surface it stops and then returns due to gravity. There is always an acceleration in the downward direction.  I have come up with two possible ways to solve this problem:   We know that $v = \frac{\mathrm{d}x}{\mathrm{d}t}$, so whenever $v=0$ then $\mathrm{d}x=0$ (i.e. no displacement in that infinitely small time). Also, $$a = \frac{\mathrm{d}v}{\mathrm{d}t} = \frac{\mathrm{d}v}{\mathrm{d}x}\frac{\mathrm{d}x}{\mathrm{d}t}$$ only if $\mathrm{d}x$ is not equal to $0$, as multiplying both numerator and denominator with $0$ will make it $0/0$ (undefined). Or multiplying by $0/0$ is not equivalent to multiplying by $1$.  Now since $\mathrm{d}x=0$ whenever $v=0$, therefore we can not write $a = v\frac{\mathrm{d}v}{\mathrm{d}x}$ when $v=0$. If we plot a $v$-$x$ curve for the motion, whenever $v=0$, as explained, $\mathrm{d}x=0$. Therefore, at that instant $\frac{\mathrm{d}v}{\mathrm{d}x}$ (the slope of the $v$-$x$ curve) will be not defined (as $\mathrm{d}x=0$), therefore the equation $a = v\frac{\mathrm{d}v}{\mathrm{d}x}$ will be undefined and we cannot determine acceleration at that instant with the $v$-$x$ curve.   Now that actually means that by plotting $v$-$x$ curve we lose information about acceleration of the particle when $v=0$.   I want a method to find the acceleration at that point using $v$-$x$ curve. Also a explanation for this defect of the $v$-$x$ curve.  Also I would like to add that so far no physics book (that I had read) has explained this before writing this relation. Also they do not mention that this will not work for $v=0$.     I would like to add the situation where I observed this: when you throw something vertically upward with velocity such that it reaches to a height 10 then the v-x curve will be-   the slope of above curve is clearly not defined at x=10(or the instant where velocity is 0) But we know that there was a constant acceleration throughout the flight. Then how can we find acceleration at that instant??? Also assume that we only have v-x curve. Or if we cannot then why??
103440
Like the subject: short sci-fi story about Earth blockaded by other human colonies.  The best humans have colonized some stellar systems. But they begin to treat humans of earth like inferiors. A war began, colonies won the war and blockaded the earth, but despite this the earth won. Who is the author?
35643
I have read the explanation for this in several textbooks, but I am struggling to understand it via Archimedes' principle. If someone can clarify with a diagram or something so I can understand or a clear equation explanation that would be great.
5385
The force of gravity is constantly being applied to an orbiting object.  And therefore the object is constantly accelerating.  Why doesn't gravity eventually "win" over the object's momentum, like a force such as friction eventually slows down a car that runs out of gas?  I understand (I think) how relativity explains it, but how does Newtonian mechanics explain it?
113724
Assume spoilers about Passengers from here, but really this has nothing to do with the plot so...  There are a number of tiny points to criticize in the film, but what I'm really coming up empty on is the math concerning where they are and how.  I think we know these things:   The ship has been on course from Earth for 30 years The ship when we meet the cast is moving at ~50% lightspeed At 31 years the ship passes Arcturus Arcturus is a red giant star ~37 lightyears from Earth and will not be much closer than that ever before it finally completes its trip across the plane of our galaxy and goes away.   So did they travel around ~37 lightyears in thirty years? Did I miss something?