I know, the title makes no sense, generally. Let me explain. I am just asking a question for which I found an answer nowhere (not even here). i think similar questions has been asked before and, no perfect answer is got(at least to what I ask).  The question is simple, why is light speed the limit for speed of particle? From many sources, I heard the answer, if we travel faster than light, we will reach somewhere before light reaches there and we will see and be in the past.   My question is, if we travel faster than light, surely we will be able to see the past. It is just because photons reach there later. We will see photons from a time before we started the journey, and probably the past. Of course it make sense. We are just seeing the past. Now we are seeing the past of sun since it take time for photons to reach here. In the same manner, we will see (and just see) the past of earth when we travel faster than light. That doesn't mean we are at the past. If we return back, we will reach the very normal time we would have felt if we neither went or returned.   I don't know if it makes any sense or not. I am not a graduate in physics. I am just 16.
Let's say I have two planets that are one hundred thousand lightyears away from each other. I and my immortal friend on the other planet want to communicate, with a strong laser and a tachyon communication device.  I record a message on the tachyon communication device and release the message at exactly the same time as I activate the laser, both of which are directed to the other planet which is one hundred thousand lightyears away. Say it is the year 0 for both of us at the time I did this.  If tachyons existed, then the message would arrive to my friend before the photons in the laser. It would arrive, say, a thousand years earlier. From my vantage point, that message will arrive to her at year 99,999; the same would be true for my friend's vantage point. However, she will only see the laser at year 100,000.  So since she got the message at year 99,999, she immediately sends me a reply back going through the same procedure as I did. She records a message and releases it at the same time as the laser. The tachyons will arrive 1,000 years earlier than the laser, so for me, I will receive the message at year 199,998. I will receive the laser, however, at year 199,999.  It seems to me that communication this way does not violate causality. I will still have received the message after I had sent it.   If tachyons truly violated causality, though, I realize it should arrive at year -1 for her, and so she can reply to me at year -2, which would mess me up by year 0 as I will ask her how she knew I was planning on sending her a message before I sent it. I could send her a different message, which she would end up receiving at year -1, and will end up confusing her as she would have received one message asking her out, and the other asking her how did she know I was asking her out. She then decides I am crazy and sends me a message at year -2 that she does not want to date me, and so she will have both turned me down and entertained me before I have even asked her out.  On the other hand, let's go back to year 0 and add a third device to our list: an Alcubierre drive. After I send out the message and the laser, I get impatient and do not feel like waiting 99,999 years, so I get on my Alcubierre drive spaceship and arrive on her planet at the same year 0. My friend is not in her office, so I leave a note to her also immortal secretary saying I dropped by and that she should expect a message for her in year 99,999.  I then get back on my Alcubierre drive and land back on my planet, still on year 0. Meanwhile, the tachyons and photons I sent out are still racing to arrive to her. By year 99,999, she receives the message just as I Alcubierre drive back to her, and I pick her up for dinner.  But the point of my question is, it seems to me that just going faster than light, if that alone was what you had, would not violate causality. It must be something else. I understand time dilation and that things with mass cannot travel at the speed of light, but using the Alcubierre drive, hypothetically speaking, I was still able to outpace the photons while also having mass. It still did not produce causality problems. Alcubierre drives are also valid solutions to GR.  It seems circular to me to say that what makes traveling faster than light violate causality is because it violates causality (if faster than light communication was divorced from causality problems, then the causality problem would cause itself -- thereby violating causality and, hence, we would scrap it and conclude that there is no causality problem after all).  What is it that I am missing? If someone could help me out, that would be excellent. I've been itching to ask my friend out for a few millenia now. :)
$a_1 a_1', a_2 a_2', ..., a_n a_n'$ is not a reduced modulo system $\mod p$. If $a_1, a_2, ..., a_n$ is a reduced residue system $\mod p$ and $a_1', a_2', ..., a_n'$ is another reduced residue system $\mod p$ then $a_1 a_1', a_2 a_2', ..., a_n a_n'$  is not a reduced modulo system $\mod p$.  Not able to show a counter to it. Help Needed. OK we are all adults here, so really, how on earth should I live without bidet? This is the part four in the interesting series: "OK we are all X here, so really". You can find the past episodes here:        Travelling always requires a bit of adjustment. While doing our favorite activity we always leave home our comfort, our routines and, unfortunately, Italians (and others) leave home their beloved .  The question is simple: what are the substitutes / tips&amp;tricks for bidet while travelling in bidet-unfriendly countries so that we can do our business without end up feeling, let's say, uncomfortable? Why are map tiles being repeated? Using MapServer and Openlayers Irreducibility check for polynomials not satisfying Eisenstein Criterion. ESM is available for 12.04, which enables Advantage customers to keep receiving kernel updates and updates for many user space packages. In our case it's very important to know if we'll be able tot use Ubuntu 14.04 safely after April '19, because it is not possible to upgrade our application and migrate it to say, 16.04. How to prove that total number of non-isomorphic labelled trees of order $n$ is $n^{n-2}$? I predicted the formula by finding total number of non-isomorphic labelled trees of order 1 is 1 , order 2 is 1,order 3 is 3,order 4 is 16,order 5 is 125.But how do i prove it ? I am beginner in graph theory so i will be very thankful if i get some simple approach to solve the problem(Not by using some difficult theorems). Use the definition of derivative to prove $\lim_{x\to 0}\ln(x+1)/x =1$ How would I use the definition of derivative to prove  $$\lim_{x\to 0} \frac{\ln(1+x)}{x} = 1$$  I got to $$\frac{\frac{\ln(1+x+h)}{(x+h)} - \frac{\ln(1+x)}{x}}{h}$$ but have no idea where to go from here.   On another site I found someones answer where they stated the following: $$ \lim_{x\to 0} \frac{\ln(1+x) - \ln(1+0)}{x-0}  = [\ln(1+x)]'\rvert_x = 0 $$ but I am unsure why the $x$ in the $x-0$ is removed. Can someone please explain? How do I use one shape to delete a portion of another shape? I have created an arrow shape (rightmost in image), from which I wish to cut out the majority so that only two thin sides remain. The most accurate way to do this would be to duplicate the shape and to somehow use the duplicate (leftmost in image) to remove the chunk that I no longer desire from the original. I am not sure what to do after the duplication, however, or if this method is even possible? Is there a better one? Is there a single word for 'without a beginning'? How to evaluate these two integrals. How do I deal with NAs in residuals in a regression in R? Showing that the roots of a polynomial with descending positive coefficients lie in the unit disc. Evaluating $\int P(\sin x, \cos x) \text{d}x$ error: parsing file '/var/lib/dpkg/status' near line 55497 package 'indicator-displex' After running an upgrade from Ubuntu 11.10 (Oneiric Ocelot) to 12.04LTS (Precise Pangolin), a window popped up saying that the upgrade failed and that I should run sudo dpkg --configure -a.  Running that command gave me:  sudo dpkg --configure -a dpkg: error: parsing file '/var/lib/dpkg/status' near line 55497 package 'indicator-displex':  blank line in value of field 'Description   Trying to run apt-get install -f gives me many dependency errors along with that same dpkg error. Why can't Inuzuka clan's dogs use human language? What does standard deviation tell us in non-normal distribution In a normal distribution, the  imparts standard deviation a lot of meaning, but what would standard deviation mean in a non-normal distribution (multimodal or skewed)? Would all data values still fall within 3 standard deviations? Do we have rules like the 68-95-99.7 one for non-normal distributions? I want to write applications for Ubuntu. I do not know much about programming but I want develop for Ubuntu. I am trying to learn Python right now. What do you think is the best way to develop apps for Ubuntu? Can you point me to some resources that can help me get started with developing for Ubuntu?  Related . Usage of "shall we?" What does it mean and where would I use it? Is the integral $\int_0^\infty \frac{\mathrm{d} x}{(1+x^2)(1+x^a)}$ equal for all $a \neq 0$? Let $a$ be a non-zero real number. Is it true that the value of $$\int\limits_0^\infty \frac{\mathrm{d} x}{(1+x^2)(1+x^a)}$$  is independent on $a$? Today I was going through my text book exercise and got hold of the following question.     Let $X$ be a normed linear space with norm $\lVert\cdot\rVert$ and $A$ is a non empty convex subset of $X$ then prove that $\operatorname{Closure}(A)$ is also a convex subset of $X$.   I gave it a try but could not succeed.