Ras72

Meaning of KE=1/2m v^2? Hi. Lay person. I was wondering about a physical meaning to the speed-energy relation. I started from the equivalence between gravity and inertial acceleration. So I hypothesize that there is the same underlying phenomenon at work; given that matter-energy warps space and that warping is gravity, I would speculate that maybe a change in velocity also entails a warping of space. In particular I thought that if a change in velocity were associated to a warping of space in two dimensions (ie. orthogonal to the direction of the force) it would explain the quadratic relation between speed and the energy required to achieve it. This (very general) idea might be relatable to the length contraction prediction of SR and it could explain the limit nature of 'c' as an upper boundary to space warping. Gravity has a gradient while inertial acceleration doesn't, but still. Does this idea have any merit? If it's implausible, why? Thanks

Ok now get it I was wrong by a few orders of magnitude Thank you

As per my OP I thought that a hypothetical spaceship travelling at 0.3c and wanting to get a probe on or around Earth could do it without massive retrofiring of propulsion. But this hinges on the probe having some unspecified, advanced shielding to make the fullest use of the gas giants upper atmospheres and to make tight turns around the sun. So the scenario is not one susceptible to reasoned arguments.

And without doing any significant braking with propulsion systems, simply with orbital manouvers and aerobraking in the gas giants upper atmospheres, it would depend on the shielding. Right? Is it possible to provide a rough estimate of how long that could take with just passive shields (best current materials tech)? If at all possible. Is it in the many years? 5? 20? (Leaving aside that without 'exotic' shielding at 0.3c it would probably be destroyed by dust anyway)

In the many movies the arrival of extraterrestrial beings or machines takes place in the form of a major ship retrofiring its main propulsion as it approaches the solar system. In my view, a much more reasonable expectation, would be for robotic probes to evasively (out basic prudence, if for no other reason) enter our system using the sun and the more massive planets to manouver and lose speed before approaching our planet to deploy and activate on orbits closer to Earth and eventually on it. It is even plausible that the entire event would never involve any major vessel coming in our vicinity; it may not even involve any contact (manifest presence) at all. This idea, after all, is neither new nor "alien"; the 1970s Daedalus study into a fusion propelled automatic mission to Barnard's star, already envisioned probes, from the ship, to arrive in the destination area years ahead. Actually all the considerations made for aliens arriving on Earth are suggestedly, equally valid with roles reversed. Is there any merit to the scenario proposed?If each probe had a mass of 5 tons, how long would it take for it to deploy on Earth's low orbit from the moment it first enters our system travelling at 0.3c?

To live you need air to breathe and water. You also want energy, and protection from cosmic rays (high speed particles coming from all directions in the Universe and capable of frying your body) On Earth protection from cosmic rays is provided by the atmosphere. Alternatively protection can be provided by a few meters thickness shielding made of lightweight polymers or water. So if you want to settle on a planet or moon other than Earth you could go to Europa. There you can create a settlement underwater. The water can be used to create air, you can separate the hydrogen and use it in a hypothetical fusion reactor to provide heat and electricity. You need to be under at least 10 meters of water to shield you from cosmic rays. Maybe 100 years from now it could be possible. (If you are thinking of terraforming, that is much more difficult If you are thinking of changing the human body to adapt to living on the surface, that probably more difficult still) So kind of like a very advanced nuclear submarine, minus the weapons (If you want weapons you can use the hydrogen from the water to make hydrogen bombs)

Ok so I answered myself. I opened a thread in the Nasa Space Flight forum and after some interference and assorted wastes of time it was established that the spectra lines would be different. So it's not a propulsion device. Good.

I read about it in Scientific American and confirmed it googling the star designation

I'd say the most efficient way to conduct planetary exploration or surveillance would be through micro robots. The way to go would be through storms of more or less intelligent, cooperating, micro and nano bots. Of course if aliens were studying us it is extremely likely that their technological level would be higher than ours. Once you assume that, then you have to admit they may have every kind of technology we consider remotely feasible and possibly beyond. In which case you can conclude that they could well be studying us right now by whatever means you can (not) imagine and we would have no way of finding out. Go paranoia go!

In September 2011 the star SDSS J102915+172927 has been observed in the Constellation of Leo. It has been found to be 20,000 times poorer in metals than the Sun which would suggest it is incredibly old (13bn years). Yet its mass is only 0.8 times that of the sun while the stars that formed at that time are thought to have had masses millions of times greater. Also the Lithium fraction is 50 times lower and it lacks the metals concentrations thought to be necessary for it to have formed. While other metals poor stars have been observed, this seems the most extreme example. So I thought, half jokingly, whether it could be... mmmhh... how can I put it... "artificial". I mean could it be, in principle, a propulsion or power device created by an advanced species, seeing how it burns almost exclusively hydrogen and helium?

In a lottery 6 numbers are extracted out of 90 (numbers 1 to 90). The numbers extracted are not put back in the bin. One can win guessing 3, 4, 5 or 6. Betters play combinations of at least 6 numbers each. I play 15 randomly composed "entirely unique" combinations of 6 numbers each. I mean that each combination is completely different from any other, so that collectively I play all 90 numbers. Each combination differing from every other in all six numbers. This way I have 100% probability of making "at least 1" which gives me a degree of satisfaction, if I switch off my brain. Also when the winning combination is extracted, I memorize the first four numbers and go through my combinations one at a time; if I haven't guessed any of the four I move on to the next one (because at best I will only have made 2 on that combination). When I have collectively guessed 4 numbers, across more combinations, I can throw away my slip since at that point I will have at best only 2 on one of the remaining played. Now, what if I wanted to play such that I had the certainty of making at least 2? Each 6 numbers combination played would have to differ from every other in exactly 5 numbers? How many combinations would that be? And how would I go about selecting the combinations starting from my 15 entirely unique ones? Thank you

Thank you. That's more along the lines was thinking of.But has any work on GR led to new predictions? As opposed to making new predictions based on GR(and eventually having them confirmed I am not doubting GR's validity or importance)

Thank you Dr Rocket. Your answer is right on point. The need to postulate the existence of dark matter and dark energy is also potentially indicative of an imperfect understanding of gravity. Wikipedia relates however of growing consensus in favor of dark matter and energy.

I'll rephrase more clearly. Aside from GR's confirmations, applications, observations. What are the major new physics and new predictions brought about by the study of GR in the last 90 years?

What have been the major contributions to our understanding of the Universe made by the study of GR from 10 years after its formulation to this day?