In 2013, ESA unveiled a map made by the Planck space telescope of the cosmic microwave background (CMB), radiation left over from the Big Bang. This idea has been a lynchpin of cosmology for decades, and recent observations have agreed with it. That’s true on the absolutely gigantic scale of the cosmos, anyway – there are obviously differences at the local scale. The isotropy hypothesis says that the universe has more or less the same properties in any direction. But new X-ray observations now suggest that this may not be the case after all – certain areas may be expanding faster than others. It was predicted by theory decades ago, and supported by measurements of the cosmic microwave background. Therefore, unlike other expansions and explosions, it cannot be observed from "outside" of it it is believed that there is no "outside" to observe from.One of the core components of cosmology is the understanding that the universe is expanding evenly in all directions. It is a property of the universe as a whole and occurs throughout the universe, rather than happening just to one part of the universe. While objects within space cannot travel faster than light, this limitation does not apply to the effects of changes in the metric itself. Therefore objects existing at a great enough distance from a potential observer are receding at a "speed" (in terms of distance/time, not motion) which exceeds even the speed of light, and they cannot be observed (due to the impossibility of a signal ever being able to traverse the ever-increasing distance between), limiting the size of our observable universe.Īs an effect of general relativity, the expansion of the universe is different from the expansions and explosions seen in daily life. To any observer in the universe, it appears that all of space is expanding, and that all but the nearest galaxies (which are bound by gravity) recede at speeds that are proportional to their distance from the observer. As the spatial part of the universe's spacetime metric increases in scale, objects become more distant from one another at ever-increasing speeds.
Instead it is the metric (which governs the size and geometry of spacetime itself) that changes in scale. Technically, neither space nor objects in space move. The universe does not expand "into" anything and does not require space to exist "outside" it. The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. It doesn't apply to changes to spacetime itself, which is what causes the universe's own expansion.
The limit on speed, the speed of light, affects objects and information within spacetime. No such matter has ever been found and there is no reason to suppose it exists. Wormholes and warp drives are permissible according to general relativity, but they require matter with negative energy density. These can be arranged into a type of superluminal travel, and are often called wormholes or warp drives. In curved spacetime it is possible for there to be multiple paths through spacetime and for one of them to be shorter than the other such that matter (always traveling slower than light locally) taking the short path can arrive before light taking the long path. Now, you asked specifically about superluminal travel. The expansion of the universe is not a speed and cannot be converted into a local speed other than 0, so it is not meaningful and therefore cannot meaningfully be compared to c. The speed of a light wave is local, and therefore meaningful, and is c. Speeds of things that are not colocated are not even well defined in a curved spacetime. This is important because in GR only local speeds are physically meaningful. Even on a local scale a light wave travels at c. In contrast, the speed of light is an actual speed. There is always a distance where the expansion between two points separated by that distance is less than c. So even then it does not make sense to compare the inflation rate to the speed of light. It was much larger in the inflationary epoch, but would still have the same units.
The expansion of the universe is currently about 70 (km/s)/Mpc. Saying that it is faster than the speed of light is “comparing apples and oranges”. The expansion of the universe is not measured in units of speed, so it cannot really be compared to c in the first place.
0 kommentar(er)
