I read that gravitational waves are so tiny that we need extremely precise equipment to detect them. I am no physicist, but GR really intrigues me and I was wondering about two things:   How powerful would a gravitational wave have to be for an average human to notice its effects, and what would those effects look like? How would these effects change as a function of the energy of the wave? What kind of cosmic event (e.g. black hole on black hole collision) could cause these gravitational waves?
Assume two black holes in the most common size range, spiraling into each other until they merge. The event releases significant amounts of energy via gravitational waves, which warp the space-time.  If the distortion is powerful enough, it would get noticed in daily life, or perhaps even detected by the proprioceptors in the human body.  How close, as an order of magnitude estimate, would you have to be to the merger to perceive it like that, without any instrument?
What happens to waves when they hit smaller apertures than their wavelenghts? I was wondering this for quite a long time now. Let's say you have a water wave (like ripples, not the ones you see during tsunamis) with wavelength 10 m. Imagine you put a boundary with an opening of 1 m. Will diffraction be observed? According to my research, no. But, then, what would be seen? Notice: Undefined variable: logged in C:\xampp\htdocs\Site\Site\view_category.php Avoiding Error 1325 EsriPyFldr not valid short file name when uninstalling ArcGIS for Desktop? I am trying to uninstall ArcGIS 10.3.1 for Desktop from Windows 7 SP1 using Uninstall a program and I am receiving an error message (pictured below):     Error 1325. EsriPyFldr is not a valid short file name.   The error message dialog appears just after:     Computing space requirements   seems to complete.  If anyone else has encountered this, then have you been able to find a way to get past it and uninstall ArcGIS 10.3.1 for Desktop?  My machine has what I would call a vanilla install of ArcGIS 10.3.1 for Desktop and ArcGIS Pro 1.1.1 so there are Python versions 2.7.8 and 3.4.1 as a result. ArcGIS Earth Beta is also on the machine.     I have made a posting on the same issue to   After running this utility () unsuccessfully (it hung for two hours before I killed it) the error message when trying to uninstall shifted to:     This action is only valid for products that are currently installed     ArcMap 10.3.1 continues to start fine and doing  wmic product where "Vendor like '%Environmental Systems Research Institute%'" get Name, Version, InstallDate, InstallLocation in a DOS window (at the suggestion of @MattWilkie) reports only the presence of Python 3.4.1 for ArcGIS Pro, ArcGIS Pro and ArcGIS Earth on my machine. What do potential postdoc advisers seek in research statement letters? I am putting together my application for a postdoctoral position in theoretical condensed matter physics. The position is not a fellowship and is a regular postdoc position. If you have gone through the process of applying for such positions a number of times, or, even better, if you have reviewed such research statement letters, what are the main points that are sought/you seek in such letters? Specifically, should I put more emphasize on my PhD research to demonstrate my "depth of knowledge" on projects I have worked on (past research), or dwell more on things that I want/am capable to do (future research)? Is it true that The Doctor can only regenerate 12 times? Why can't this be done with Master Theorem Apparently recurrences like this cannot be solved with the Master Theorem:  $T(n) = 2T\left(\frac{n}{2}\right) + \frac{n}{\log(n)}$  Because $n^{\log_b(a)} = n^1$ is not a polynomial multiple of $f(n) = \frac{n}{\log(n)}$ since $\frac{n}{\frac{n}{\log(n)}} = \log(n)$, which is less than $n^\epsilon$ for any positive $\epsilon$.  But when is this really even an issue?   For example why wouldn't the time complexity be $n \log n$ using case 2 of the Master Theorem? Unrolling the recursion:  $$T(n) = n\sum_{k=1}^{\log_2(n)} \frac{1}{\log_2(2^k)}$$  $$T(n) = n\sum_{k=1}^{\log_2(n)} \frac{1}{k}$$  Doesn't this suggest $\Theta(n \log n)$ even though it supposedly cannot be done with Master Theorem? My chain broke and in a moment of silliness (I was cold wet and slightly annoyed)  I threw the broken one away before thinking about measuring the new one.  Is there a guide to getting the chain length/tension correct ?  It's an 8 speed road bike (Shimano Sora back, double ring front) Can "cattle" be singular? I've grown up on a farm, and my dad and his dad, apparently, always used "cattle" to refer to both the singular and plural forms of the domestic bovine. I've always assumed it's how the word "deer" is.  However, I've heard people say that this is incorrect and the singular is just "cow", but this has always offended us as a cow is a mother cattle, and is incorrect if you're referring to a steer, a bull, or a heifer.  So, is cattle singular as well as plural? If not, is there some general, non-gender-specific word that should be used instead? I believe it's a common practice in some communities to name children after their grandparents or parents or relatives and sometimes even friends and popular people. Places, roads, streets etc., get named after famous people, too. Many inventions and discoveries have been named after people who invented or discovered them.  But I am not yet aware of a term that refers to the person whose name is given to people, places or objects this way. Is there a suitable word to fill in the blank below?     They named their son after the famous football player, David Beckham.      David Beckham is .......... of their son. The Earth is spinning, so why don't we jump and land on a different location? I know there are similar questions on StackExchange but I think it is different and detailed.  The earth is spinning 465 meters/second so why don't we jump and land on a different location?  I googled about this question and I got some answers:   When we jump, we (and the atmosphere itself) also spin along with the earth so we don't land at a different location. (But why we are also spinning along with earth ?) The earth is so big and we are very small relative to earth so the tiny jump won't make any difference.   But according to answer 1, We are also spinning with the earth. But the question is, "why are we also spinning along with earth" ??  Regarding the answer 2, it won't make any difference but logically it doesn't make sense or I just don't understand it.  Here is the followup question,   "When we jump why don't we thrown out of earth due to centrifugal force of the spinning earth ??"  Please provide some detailed answer to these questions. With logic if possible.   This phenomenon is not possible I know, but even if it exists, then traveling will be so easy, we just have to hang on space (with help of helicopter etc.. ) and we can travel the whole world in 24 hours :D In C, how do I restrict the scope of a global variable to the file in which it's declared? What if the Earth stops in its orbit and instead falls straight towards the Sun? The Earth orbits around the Sun because it has angular momentum. If we stopped the Earth in orbit and then let it fall straight towards the Sun, how long would it take to reach the Sun in seconds?  Details and assumptions  The mass of the sun is 2*10^30 Kg. The mass of the earth is 6*10^24 Kg. The earth is 149,600,000 Km from the Sun. You may treat the Earth and Sun as point masses. How to integrate mv command after find command? I am searching for files which name which contain AAA within their path using following command:  find path_A -name "*AAA*"   Given the output showed by the above command, I want to move those files into another path, say path_B. Instead of moving those file one by one, can I  optimize the command by moving those files right after the find command? How do I use itertools.groupby()? I haven't been able to find an understandable explanation of how to actually use Python's itertools.groupby() function.  What I'm trying to do is this:  Take a list - in this case, the children of an objectified lxml element Divide it into groups based on some criteria Then later iterate over each of these groups separately.  I've reviewed , but I've had trouble trying to apply them beyond a simple list of numbers. So, how do I use of itertools.groupby()?  Is there another technique I should be using?  Pointers to good &quot;prerequisite&quot; reading would also be appreciated. Sum and product of Martingale processes Given two Martingale processes $(X_t)$ and $(Y_t)$, are their sum $(X_t+Y_t)$ and their product $(X_t \times Y_t)$ also Martingale?  If not, will the two $(X_t)$ and $(Y_t)$ being independent grant their sum and product Martingale? Thanks! Indefinite integral $\int(\sin x)^2/(x\cdot\cos x-\sin x)^2\,dx$ How to find the antiderivative of $\dfrac{(\sin x)^2}{(x\cdot\cos x-\sin x)^2}$? I know that series theory can solve the problem. But I wish to solve the problem by the antiderivative way. The numerator and denominator divide the $x^2$ at the same time, don't they? Why is my network interface named enp0s25 instead of eth0? A lot of my scripts stopped working after installing Ubuntu 15.10 and I have trouble remembering this new name as I was used to ethx and wlanx for years. Is there a reason for this change? Do I have to get used to this or can I just rename it and go back to good old eth0?  $ ifconfig  enp0s25   Link encap:Ethernet  HWaddr 77:5a:5e:a6:86:d5         inet addr:192.168.31.239  Bcast:192.168.31.255  Mask:255.255.255.0       inet6 addr: fe80::725a:b6ff:fea6:86d7/64 Scope:Link       UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1       RX packets:4833 errors:1332 dropped:0 overruns:0 frame:666       TX packets:5589 errors:0 dropped:0 overruns:0 carrier:0       collisions:0 txqueuelen:1000        RX bytes:3266446 (3.2 MB)  TX bytes:1046654 (1.0 MB)       Interrupt:20 Memory:d3500000-d3520000 Evaluate the integral $\int_{-1}^1\frac{dx}{(e^x+1)(x^2+1)}$. Evaluate:      $$\int_{-1}^1\frac{dx}{(e^x+1)(x^2+1)}$$ How can I find and replace specific words in a text file using command line? I would like to know how to unload an assembly that is loaded into the main AppDomain.  I have the following code:  var assembly = Assembly.LoadFrom( FilePathHere );   I need/want to be able to unload this assembly when I am done.  Thanks for your help.