Jump to content


Resident Experts
  • Posts

  • Joined

  • Last visited

  • Days Won


Everything posted by Janus

  1. In d = vt, all three are measured by Bob. v = 0.986c and t = 5 y, so d = 4.93 LY Alice would measure 'd = vt', for her v = 0.986c and t' equals 0.833 y, so d' ( the distance between planets) is ~0.822 ly To use length contraction, Alice would use d/y = d' or 4.93/y = 0.822 LY, which is the same answer.
  2. If you by this you mean that Bob can measure Alice as being length contracted, but Alice can't measure Bob as being length contracted, then you're wrong. Or let's put it this way: Assume there is a planet 4.93 ly from Bob as measured by Bob, to which Alice is traveling. Then, as measured by Alice, this planet and Bob are only ~0.822 ly apart. Bob and this planet is traveling at 0.986c relative to Alice, and thus Alice measures 0.822 ly/0.986 = ~0.834 yr between Bob passing and the planet passing.
  3. But since the OP specifically used "BC" and "AD", which are not used in the Hindu calendar, that is not relevant here.
  4. I went back and corrected the typo, that 1339 years should have be 4399 years . The Gregorian calendar wasn't introduced until 1582, so it wouldn't have been in effect over this time period. But even if you take the difference between 1399 Julian years and 1399 Gregorian years, it only works out to be ~34 days.
  5. 4399 years. As there is no year 0, there is only 1 year between the start of 1 BC and 1 AD, and between the start of 1AD and the start of 1400 AD, there are just 1399 full years.
  6. No, you were not. You were told that posting a video alone, so that someone has to watch the video in order to participate in the thread is against the rules, as stated in this quote from the rules. "Links, pictures and videos in posts should be relevant to the discussion, and members should be able to participate in the discussion without clicking any links or watching any videos. Videos and pictures should be accompanied by enough text to set the tone for the discussion, and should not be posted alone." You weren't told that you can't post any videos, just that that you didn't follow the proper rules for posting videos.
  7. Any pardon Pence issued could only cover federal crimes, It can't apply to cases being prosecuted at a state level such as those in New York. Oh, And I can make at least one prediction for the Biden Presidency - Obama will finally get his portrait hung in the White House.
  8. I assume that the Dutch version is similar to the Finnish "salmiakki". I've tried two versions. One was soft, a bit salty and quite good. The other was harder and much stronger on the ammonium chloride taste. While I was taken back at first by the second one, and can see why many people wouldn't like it, I kept giving it a chance, ended up finding it oddly addictive, and finished the box.
  9. Gravity is is a "curvature" of space-time. But this doesn't mean that anything is physically "bent". It is a term used to express that the geometry of space-time is non-Euclidean. Non-Euclidean geometry is often described as being like doing plane (2 dimensional) geometry on a 3 dimensional curved surface ( like a sphere), But this is just an easy way to visualize it. Non-Euclidean geometry doesn't require an added dimension.
  10. Generally to create a paradox you would have two inertial frames in relative motion, each capable of instantaneous information transfer within themselves. Example: You are in a spacecraft which passes Earth at 0.8c as both your and the Earth clock reads the same. Trailing 1 ly behind you ( as measured by you) is another spacecraft. 1.25 yrs later, by your clock, you are 1 ly from Earth and the trailing craft is next to Earth. The time on earth is just 0.75 years later than when you passed it. (An Earth observer would also agree that the trailing craft passed the Earth 0.75 years after you passed. At that moment, you transmit an instantaneous message to the trailing craft, and that craft hands it off to the Earth as it passes. The Earth, in turn, send this message to a buoy floating in space which is 0.6 ly away and long your path. Because, in 0.75 yrs at 0.8 c, that is how far you have traveled from the Earth. So you will be right next to that buoy. Your clock will read 0.45 yrs past what it read when you passed Earth. You will also agree that you passed the buoy when you clock reads 0.45 yrs, As the 0.6 ly distance ( as measured by the Earth) is 0.36 ly as measured by you, and it take 0.45 yrs to travel that distance at 0.8 c. The buoy hands the message off to you as you pass it. Thus a message you sent 1.25 yrs after leaving Earth is received by you 0.8 yrs before you sent it!
  11. When you arrive at point C, you will see the same light coming from both stars as someone who never moved from point C; Light that left both stars 5 yrs ago. You see both stars as they were 5 yrs ago.
  12. 1-v^2/c^2 is not the same as (1-v^2)/c^2 So for example, again using v= 0.6c 1- (0.6c)^2/c^2 = 1- 0.6^2 = 0.64 but (1-(0.6c)^2)/c^2 = 1/c^2- 0.6^2 = 1/c^2 - 0.36 1-v^2/c^2 = (1-v^2)/c^2 is like saying (1-1/2) = (1-1)/2 but solving the left side gives 0.5 and solving the right side gives 0
  13. To start off. 1 / Gamma = √ 1 - v^2 c^2/ c^2 = c / Gamma = √ 1 - v^2 +v^2 You have to multiply all the factors under the radical by c^2 if you want to move c to the other side of the equation This leaves c/Gamma =√ (c^2 - v^2) And since c^2 ≠ 1+v^2 you can't get to where you got. And at the end, your answer is not a multiple of c, so that right there should have been a tip-off that you did something wrong along the way. To solve for v from 1 / Gamma = √ 1 - v^2/c^2 You first square both sides: 1/Gamma^2 = 1- v^2/c^2 (you square both the 1 and gamma, but since 1^2 = 1...) v^2/c^2 = 1-1/gamma^2 v^2 = c^2(1-1/gamma^2) take the square root of both sides: v= c√(1-1/gamma^2) Thus if v = 0.6c Then Gamma = 1/√(1- 0.6c^2/c^2) = 1.25 and v = c√(1-1/1.25^2) = 0.6c
  14. TIL that a skilled scam-baiter can waste 36 hrs of a scam call center's time in an attempt to scam one person. I recently have been watching some you-tubes edited from the Twitch live-stream of a scam-baiter. They can be entertaining, while giving you a look into just how many these scams work. (he has done tech support, fake refund, IRS, social security, and immigration scams) One of the best was when he faked going to Best Buy to buy gift cards for the scammer, only to have his Uber driver drive off with them. ( this one required sound effects and a friend playing the part of the driver.) Generally, he can't waste their time for more than an hour or two at most before the scammer either gives up or the scam-baiter just reveals himself. In this case, in an attempt to scam someone, who they thought was an 87 yr old woman, this call center, over many, many phone calls spread out over weeks, spent 36 hrs on the phone with their intended victim. The edited you-tubes of this was broken up into 10 episode of ~ 3/4 - 1 hr long each, and I just watched the last one. It was interesting to see how the baiter kept them on the hook, always teasing with a big score that never came, and how more and more desperate the scammers got.* *And in this case, it lead them to revealing just a bit too much info, which the scam-baiter turned over to authorities.
  15. That "Narrow band" is a lot wider than it looks to the naked eye. You are only seeing that part that is bright enough. As an example, consider the Andromeda galaxy. To the naked eye it looks like a small fuzzy spot, but if you could see it in full, it would appear like this in the sky. Several times wider than a full Moon. What we see by naked eye is just the nucleus of the galaxy. But just because we don't see the disk by naked eye doesn't mean that it doesn't hide the light from galaxies behind it.
  16. Each set of images shows a series of chosen moments for each frame. Those moments are chosen as they represent when a pair of clocks pass each other. The numbers tell us what clocks at those positions read at that moment according to the chosen frame. So each successive diagram in the image represents a single moment in time. Thus in the first image of the first set, All the clocks on the E-X rod read the same time(12:00) at that moment, while the clocks along the B rod do not ( reading 12:00, 11:31:12, and 11:12 as you go from left to right) at that same moment.
  17. Spacecraft during re-entry only get up to ~ mach 25, and even at that speed, the air is heated to a plasma state. Craft like Apollo and Soyuz use ablative shields that burn off to deal with it. And this is in the upper part of the atmosphere, where the air density is very low.
  18. Your error is that you again are not taking relativity of simultaneity into account. To illustrate, we can put clocks at the end of rod attached to B and at the point's along the rods. Thus from The E-X rest frame you get this: The green boxes indicate two clocks passing each other and their respective readings as they do. In the rest frame of B, you get this: Comparing the the times shown in the green boxes as clocks pass each other agree with those in the first image. In each image, there is a an instance when two pairs of clocks pass at the same time, but they are different pairs of clocks in each image. This just illustrates that, with the Relativity of simultaneity, events that are simultaneous for one frame of reference are often not simultaneous for another.
  19. About 10% of the universe is "hidden" from our view by the bulk of our own galaxy (20% if you only consider the visible part of the spectrum). This won't change much due the rotation of the galaxy as this is mostly due to having to view through the disk of the galaxy.
  20. My mistake, I thought you were here for a rational discussion.
  21. While not intentionally, a fix to a design problem provided one. One of NASA's missions to a moon of an outer planet required communication between an orbiter and lander. This used a protocol which involved a narrow frequency tolerance. The problem arose because the tolerance was made too tight and the transmission frequency of the lander was off just a bit. The "fix" they came up with was to alter the orbiter's orbit so that at specific times, its velocity with respect to the Lander caused a Doppler shift which compensated for the drift. The lander would dump its gathered data during these "window"s. Now if there had been an "ether wind", the Moon's orbit around its planet, and the Planet's velocity would have had an effect on that Doppler shift. In other words, Not only would they had to account for the relative velocity between lander and orbiter, but these other motions as well. And since these motions changed with time relative to the orbiter's orbit, NASA would have had to either keep adjusting the Orbiter's orbit or changing the "transmission window" to keep up. They didn't. The only thing they needed to concern themselves with was the relative velocity between orbiter and lander, which would not have worked if there had been an ether wind. T
  22. Personally, I subscribe to Bertrand Russel's version of liberalism. It's not the views you hold, but how you hold them. Always cognizant of the possibility that they could change upon the discovery of new information.
  23. The reason the tidal interaction transfers angular momentum from Earth to Moon is that the drag between the Earth and tides causes the tidal bulges to be pulled "ahead" of the Moon. If you removed this drag completely, the bulges would remain lined up with the Moon, and there would be no momentum transfer. Increasing the drag would allow the spinning Earth to pull the bulges even more out of line, increasing the tendency transfer energy to the Moon. As far as energy goes: Most of the energy lost by the Earth through its slowing rotation is not transferred to the Moon, but is lost as heat.( the Moon gains less orbital energy than the Earth loses rotational energy). So it doesn't really work to think of energy "used" by the turbines as being taken away from energy given to the Moon. Look at it this way. If we just increased the drag without generating electricity, we would increase the amount of energy the Earth loses in rotational energy both by transferring some to the Moon, and by waste heat. By extracting some of that energy by converting it to electricity, you are making use of a part of that energy that would have been lost as heat.
  24. So, I read that Trump planned his town hall after hearing about Biden's, and his intent was to "blow Biden out of the water" in the the viewership ratings ( you know how important Trump thinks TV ratings are). The ratings came in: Biden's were better. Trump's blood must be boiling, and I wouldn't want to be the flunky he' s going to lay the blame on.
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.