We now have to find a different definition of spacetime because the local definition will not make any sense. The universe did not start at a point, it has no centre and it has no edges.
Look up the number of times these questions have been asked here already. So on a global scale , we in my opinion , need to redefine spacetime as the relationship between objects in the universe and reconsider the idea that geometry and continuous 4D differentiable manifolds are the complete solution to the spacetime of the observable universe. Geometry may be of no use when describing an electron, and the beginning of the universe was "smaller" than that. It is also not useful in describing the interior of black holes or if we discover that spacetime is actually discrete.
A long shot, I appreciate that. So at both scales of the universe, at its "smallest", and at its "biggest", remember we are in an expanding universe , the descriptions of the other answers of what space "is" fail us, they simply do not apply. In summary, on a local scale, I believe that the geometry and coordinate system, while you may consider that they simply replace one word for another and avoid telling you what spacetime really "is", because that is not the job of physics in the first place , they are essential if we are to keep track of our measurements on a local scale.
A caveat here is that a closed universe may "kinda" have an edge, in that if you start at any point you may return to it, but the evidence points to a flat but expanding universe. So I ask you to consider you a description of spacetime on a global scale as a set of relationships. I think this is more appropriate, in fact the only way, we can deal with what spacetime is, on a universal scale.
Using the handwavy word "relationship" brings in QM, which will need to be brought in anyway if we want to achieve a quantum gravity theory, but I have now moved from a personal opinion, to complete uninformed speculation.
Time to stop. My sincere apologies to those concerned, for the number of edits in this post, I will not repeat this practice in future. Nobel laureate Robert B. Laughlin has some interesting things to say about general relativity and ether. I'll quote from his book "A Different Universe". Laughlin is discontent with the strategies and underlying dogmas of modern physics; in the book he tries to provoke us out of our comfort zone.
The book's gist is that modern physics, focusing on elementary particles and increasingly smaller and detached details, misses the point: The emergent phenomena whose underlying building blocks are secondary — much like it is secondary whether a house is built from brick or granite blocks.
With respect to gravity he argues that dogmatically insisting that there is no ether makes us miss the emergent properties of space time. Acknowledging and exploring those would be more relevant and productive than trying to pinpoint the increasingly narrow and irrelevant details on the elementary level, a strategy which he dismisses as reductionist.
The equations Einstein proposed to describe gravity are similar to those of an elastic medium, such as a sheet of rubber. The irony is that Einstein's most creative work, the general theory of relativity, should boil down to conceptualize space as a medium when his original premise was that no such medium existed.
But this same thought process led in the end to the very ether that he had first rejected, albeit one with some special properties that ordinary elastic matter does not have. The word "ether" has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connections, it rather nicely captures the way most physicists actually think about the vacuum.
The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo. The clash between the philosophy of general relativity and what the theory actually says has never been reconciled by physicists and sometimes gives the subject a Kafkaesque flavor. On the on hand, we have the view, founded in the success of relativity, that space is something fundamentally different from the matter moving in it and thus is not understandable through analogy with ordinary things.
On the other, we have the obvious similarities between Einstein's gravity and the dynamic warping of real surfaces, leading us to describe space-time as fabric. Bright young students inevitably pick up on this and ask the professor what moves when gravitational radiation propagates. They receive the answer that space-time itself does, which stops them cold. It is like learning that the surface of the sea undulates because it is an undulating surface. See this wiktionary entry. There is spacetime to bend.
The understanding of spacetime becomes vital to understand bending. In this case, the mass is still taken up space but not at the same point of space, over time. If we stop time it takes up x amount of space. The lead edge of the mass in motion is causing space to contract, while the rear edge of the motion, is where it is making more space available.
We see this as the Doppler shift. During the beginning of the universe, when mass appeared in a concentrated place; primordial atom, it took up all the local space; extreme density. Space from afar needed to rush in to fill the space vacuum. The smaller mass is not "attracted" to the larger mass by any force. The smaller mass simply follows the structure of curved spacetime near the larger mass. For example,the massive Sun curves spacetime around it, a curvature that reaches out to the edges of the solar system and beyond.
But if a gravitational wave comes rippling through space while the detectors are switched on, that ripple will stretch one arm of the L-shaped structure before stretching the other. The gravitational wave distorts the passage of the light, resulting in a particular kind of interference light pattern detected at the end.
On 11 February , the LIGO teams announced the direct discovery of a gravitational wave matching the signal predicted from the collision of two black holes. Astronomers at the Background Imaging of Cosmic Extragalactic Polarization BICEP2 telescope had supposedly discovered evidence of gravitational waves, but that evidence was later recalled, as it did not pass closer scrutiny. Rather than listening for the direct signal of a gravitational wave as it rolled past our planet the setup at LIGO , the BICEP2 team analysed swirls of light within the cosmic microwave background GLOSSARY cosmic microwave background The faint remnant of light that permeates the whole universe, left over from the heat of the big bang.
They theorised that during the early expansion of the universe, tiny gravitational waves would have disturbed the light around them, which would have been amplified into a larger pattern as the universe expanded, coalescing into these patterns in the cosmic microwave background.
The announcement was made before the BICEP2 data went through more rigorous analysis and feedback from their colleagues. Instead, it looked likely that the patterns of light were not caused by gravitational waves, but instead by the dust inside our own galaxy as it interacted with magnetic fields.
The successful LIGO experiment has ushered in a new era of astronomy. Before now, astronomers have largely focused on the study of the electromagnetic spectrum including light and radio waves.
What we do know is that this technique will allow us to better understand the most massive objects in the universe such as black holes, neutron stars, and supernovae; and it will provide us with a new window to study how the universe formed. One unanswered question is whether or not gravity is propagated by the graviton—the proposed but so-far undetected particle responsible for gravitational interactions.
Even more pressing, we know that general relativity is, in its current form, incompatible with the other pillar of modern physics: quantum mechanics GLOSSARY quantum mechanics A branch of physics that explains how the universe works on incredibly tiny scales atomic and subatomic.
But it has produced many unexpected, unintuitive predictions that have been confirmed again and again for over a hundred years. This has been one of the greatest journeys in the history of science, involving not just Newton and Einstein, but thinkers and doers all around the world who have worked to put these theories to the test.
Even so, the schism between relativity and quantum mechanics remains. However, there are a few theories—stringy, loopy, multi-dimensional theories—unproven but with promise of becoming the next milestone in understanding our cosmos. Understanding gravity—warps and ripples in space and time Expert reviewers.
Isaac Newton and Albert Einstein were pivotal in advancing our understanding of gravity. Newton and the laws of gravity Newton published one of the most celebrated works of science, the Principia , in Newton realised that gravity was responsible for objects falling to the ground and for the orbit of celestial objects. Newton was well aware of this when he said, Gravity must be caused by an agent acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers.
Isaac Newton. Experiments in a smooth-moving vehicle yield the same results as experiments conducted on land. Space and time are linked Almost years after Galileo, Einstein pondered the consequences of relativity in the context of an important factor: the speed of light.
Show labels Stop Start. Stationary vs moving light clocks in slow motion As seen from inside the spaceship As seen by a stationary observer.
0コメント