A NASA mission called Gravity Probe B (GP-B) measured the shape of the space-time vortex around the Earth in 2011 and found that it closely accords with Einstein's predictions. SJBauer said:A well written summary for the definition of space-time. I like the history and the introduction of how space-time works, but the focus on a reconciled quantum mechanical model to explain gravity seems like a math problem. A more logical approach might be to consider the 'Big Bang' theory from a pre-existing fabric of space-time without any real matter, as a proposed one dimensional determinant, its inception starts with the unfolding perspective of this dimensional determinant for space-time fabric towards existence. The sequence is somewhat understood from an expansion from our one dimensional space-time into a two dimensional space-time fabric, and then into a three dimensional space-time fabric, and so on. The expectation is that ordinary matter creation took place within a pre-existing dark energy medium of space-time. Indeed, the existence of matter would be an intrusion upon this pre-existing universal medium of space-time which maintains a zero sum difference that is the balance of our cosmological continuum. What Is Space-Time? Well, we can only measure 4D spacetime relative to energy density (mass density) concentrations...which concentrations are themselves 4D spatially-extended energy density and mass density integrations. So a new 4D spatially-extended nonstandard model of energy density and mass density integrations is going to be required to resolve the Quantum Crisis, since as Alessandro Fedrizzi and Massimiliano Proietti found Objective Reality Doesn't Exist, Quantum Experiments Shows. Let's start with Albert Einstein's theories of relativity, which set out a description of space, time, mass and gravity. A key outcome of relativity is that the flow of time isn't constant. Time can speed up or slow down, depending on the circumstances.

One of the peculiar observations that has emerged from the study of the quantum realm is non-locality. A change in a particle's state in one location can instantaneously influence another "entangled" particle somewhere else – something Einstein referred to as "spooky action at a distance". This has been " shown experimentally many times" in Nobel Prize winning research, says Adlam. Even if we could, says Vedral, we wouldn't want to. "You would literally be repeating exactly the same thing over and over again," he says. You sort of in some sense would be sending a signal to the past, but only by destroying all the records of everything that happened," says Adlam. "You wouldn't be able to make practical use of that, because you necessarily had to destroy the records of succeeding and sending that signal."

The VLBI technique provides direct access to the ICRS and is the best technique for observing the full set of EOP. Specifically, VLBI is the only technique able to determine the position of the celestial intermediate pole in the ICRF, expressed as celestial pole offsets to a conventional precession/nutation model, and the Earth’s rotation angle, typically referred to as Universal Time or UT1–UTC. Table 1 summarizes the parameter types and the space geodetic techniques contributing to their determination. The table also shows the parameters that can be used for a co-location of the techniques, both, on the surface of the Earth and in space. Satellite techniques rely on measurements between stations on the Earth’s surface and satellites, whose orbits are subject to various gravitational and non-gravitational forces (e.g., SRP). As a consequence, SLR, GNSS and DORIS depend on a reference frame that is dynamically realized by satellite orbits and thus completely different in nature from the kinematic realization of the ICRS by VLBI. Presently, the only physical connection between the VLBI frame and frames of SLR, GNSS and DORIS is via the local ties on the ground; however, these ties reveal significant discrepancies with respect to the terrestrial frames delivered by the individual space geodetic techniques. The TRF is the realization of the TRS and is currently provided by precisely determined coordinates and velocities of physical points on the Earth’s surface. The main physical and mathematical properties of a TRS (at the definition and conventions level) or of the TRF (at the realization level) include each its origin, scale, orientation, and their time evolution. The center of mass (CM) of the Earth System, or geocenter, as the realized origin of the TRF on long-term scales, needs to be accurately determined including its temporal motion (e.g., Petit and Luzum 2010). The temporal variations of the geocenter represent a component of mass change (at spherical harmonic degree one) that is not directly observable from a mass-change mission such as GRACE-FO (Wu et al. 2012). While the degree one component of mass change can be derived from a combination of GRACE data with ocean model output (e.g., Swenson et al. 2008; Sun et al. 2016, 2017) or space geodetic techniques such as GNSS, SLR (e.g., Fritsche et al. 2009; Glaser et al. 2015), a high-quality TRF solution furnished by space geodesy that allows a matching with the temporal resolution of the GRACE-FO data would be highly desired (see section Long-wavelength gravity field for more details). Direct local observations and space geodetic techniques including gravimetry, radar and laser altimetry, optical and synthetic aperture radar imagery and GNSS, have provided clear evidence for large changes in the world’s glaciers and ice sheets, in response to present climate change (e.g., Shepherd et al. 2018, 2020; Millan et al. 2022; Fox-Kemper et al. 2022). However, despite the extensive literature on the subject, the ice mass balances over the different ice sheets and smaller glacier regions are associated with large uncertainties (e.g., Cazenave et al. 2018; Métivier et al. 2010; Khan et al. 2015). In particular, the question of possible local accelerations of ice mass loss in Greenland is still open (e.g., Velicogna and Wahr 2013; Velicogna et al. 2014, 2020). As mentioned before, we expect that GENESIS will improve the determination of the reference frame. Such a stable ITRF should drastically reduce the frame dependency of ice mass balance estimations. Geodynamics, geophysics, natural hazards But what about in the real world? Could we ever build a time machine and travel into the distant past, or forward to see our great-great-great-grandchildren? Answering this question requires understanding how time actually works – something physicists are far from certain about. So far, what we can say with confidence is that travelling into the future is achievable, but travelling into the past is either wildly difficult or absolutely impossible.

This is best understood by thinking through an experiment. Suppose Adam conducts a measurement in the lab. However, the result he gets is dependent on a measurement that Beth does later. In other words, Beth's experiment in the future controls the outcome of Adam's experiment in the past. However, this only works if Beth's experiment destroys all the records of what Adam did and saw. An error of a few tenths of mm/year in the frame origin stability estimation is well known to have a large impact on the orbit calculations of satellites and in the water mass redistribution on the surface (see Table 2). Nowadays uncertainty in the long-term trends in the geocenter motion of ±0.3 mm/year leads to uncertainties in the Antarctica mass change of 18 Gt/year (Wu et al. 2012; Blazquez et al. 2018). Although the ITRF2020 long-term origin is defined solely by SLR, weaknesses in its realization include the poor number and geometry of SLR stations in operation today: the number of the most prolific SLR stations does not exceed 16, and not all of these stations have the same level of performance. The only internal evaluation that can be made is the level of agreement between ITRF2020 and previous ITRF versions, namely ITRF2005, ITRF2008, and ITRF2014 whose origins were also defined using SLR data submitted in the form of time series. ITRF2020 results indicate that the agreement in the origin components, with respect to the past three ITRF versions, is at the level of 5 mm in offset and 0.5 mm/year in rate, values that are still far away from the science requirements. So there we have it. On our current understanding of the Universe, we could potentially travel into the future, but travelling into the past may well be a total no-no. It isn't even possible to send a message into the past, says Adlam. "The retrocausality is very specifically hidden by the way it's implemented."

#POURMOILOVES

Real wormholes would also be microscopically tiny. You couldn't fit a person, or even a bacterium, through one. It's also not at all obvious how we could make such a thing. "Even if we had much greater technological powers than we currently do, it seems unlikely that we would be able to create closed time-like curves on purpose," says Emily Adlam, a philosopher at Chapman University in California, US. The LEGO TIE Bomber features what LEGO describes as "built for battle play" features, but it'll also look great on any display shelf.

CRF, TRF, and the Earth Orientation Parameters (EOP) that describe the transformation between these two frames are fundamental for any kind of positioning on the Earth and in space and provide most valuable information about the Earth system. The International Celestial Reference System (ICRS) is a quasi-inertial reference system defined by extragalactic radio sources, mostly quasars, billions of light years away, and is realized as International Celestial Reference Frame (ICRF) with a set of quasar coordinates with a noise floor of about 30 \(\mu\)as (Charlot et al. 2020). The positions of a set of globally distributed radio telescopes are determined using the difference in the arrival times of the signals at the different telescopes (Sovers et al. 1998). Relativity means it is possible to travel into the future. We don't even need a time machine, exactly. We need to either travel at speeds close to the speed of light, or spend time in an intense gravitational field. In relativity, these two acts are essentially equivalent. Either way, you will experience a relatively short amount of subjective time, while decades or centuries pass in the rest of the Universe. If you want to see what happens hundreds of years from now, this is how to do it. Given that GENESIS will provide a direct link between the kinematic (VLBI, quasar-based) and dynamic (satellite-based) reference frames and is expected, thus, to improve the consistency of the TRF, CRF, and EOP realizations, all the above scientific domains will be positively impacted, extending thus the challenges of GENESIS well beyond its first scope. The ITRF long-term origin is defined by SLR, the most accurate satellite technique in sensing the Earth’s CM. The ITRF long-term scale, however, is defined by an average of the SLR and VLBI intrinsic scales. The consistency of these scales still needs to be improved, since both techniques are subject to systematic errors and other technical limitations, such as time and range biases for SLR, antenna deformation for VLBI, etc. The GENESIS mission will help to solve these inconsistencies. The ITRF orientation and its time evolution are defined to be the same for the successive ITRF realizations. This is where time travel can come in and it is scientifically accurate and there are real-world repercussions from that," says Emma Osborne, an astrophysicist at the University of York, in the UK.

Cancellation & Returns

Observed ground movements at the Earth surface are manifold and related to a whole set of processes. Common and essential to all these movements are detection and monitoring to execute and develop risk assessment strategies. Natural hazards, such as earthquakes, volcanic hazards or landslides may be preceded by small displacements of the Earth’s surface. Dense networks of GNSS stations in Japan, the western United States, and South America have been installed to monitor these surface displacements, related to the seismic cycle. In particular, pre-earthquake surface deformation can be related to the stress and the state of stress in the lithosphere. Surface displacements from increasing stress in the lithosphere may have small amplitudes. Therefore, a very stable and precise reference frame is required to be able to interpret these observations as reliable prediction tools for the onset of hazards versus errors in the techniques themselves. Top of atmosphere radiation budget and Earth energy imbalance

Up to now the geocenter motion is traditionally measured by SLR using the observations to geodetic satellites (see Fig. 3). The geodetic satellites such as LAGEOS or LARES are considered to be well suited for determining the geocenter motion owing to their mission characteristics, such as orbit altitude, low area-to-mass ratio, and thus minimized non-gravitational orbit perturbing forces. Until now, determination of geocenter coordinates based on the SLR observations to active Low-Earth Orbit (LEO) satellites was limited because of issues in non-gravitational force modeling acting on LEO satellites. In principle, the geocenter coordinates should be well determined from any satellite mission that is continuously observed and has processed orbits of superior quality. Therefore, GENESIS can introduce an alternative for the geocenter recovery w.r.t. passive geodetic satellites. While time travel is fundamental to Doctor Who, the show never tries to ground the Tardis' abilities in anything resembling real-world physics. It would be odd to complain about this: Doctor Who has a fairy-tale quality and doesn't aspire to be realistic science fiction.and the Very Long Baseline Interferometry (VLBI) technique, which normal operation is to record signals from quasars. So much for time travel based on relativity. What about the other great theory of the Universe: quantum mechanics? The Po Theory is a new theory of physics presenting fundamental issues, among others construction of space-time and describes the properties of space-time, e.g. its decay (expansion) resulting in the generation of time. In The Po Theory there are many models describing the structure of matter, e.g. particle generation model, particle mass (energy) generation model, preon structure model, etc. All these models are supported by mathematical equations describing the properties of particles such as particle radius, its mass, characteristic time associated with the particle, life time, range of interaction. The Po Theory gives, for example, a formula for calculating the radius of an electron, its mass or electric charge. On shorter timescales, GNSS stations also record Earth’s elastic response to surface mass redistribution within the climatic system (mainly continental water storage, atmosphere and ocean). Dense networks of permanent GNSS stations can now be used to derive soil and snow water content at seasonal timescales, but has also provided evidence for extreme droughts, especially in California (see, e.g., Argus et al. 2014; Fu et al. 2015; Jiang et al. 2022). GNSS time series from dense networks can be used to refine the information provided by space gravimetry missions (GRACE and GRACE-FO) at longer spatial wavelengths (see section Long-wavelength gravity field). Amplitude and spatial extent of surface water mass variations can be inferred from both vertical and horizontal deformation measurements. In particular, horizontal displacements help to refine the determination of the location and the spatial extent of the load. This elastic Earth’s response to surface loads has to be separated from a longer-term deformation, which can only be obtained with a more accurate and stable reference frame as proposed by the GENESIS project. GENESIS can provide independent estimates of the low-degree Stokes coefficients based on all geodetic techniques. SLR studies and simulations showed that adding one satellite to a solution based on five SLR satellites may significantly improve the determination of the low-degree spherical harmonics of the Earth gravity field (Bloßfeld et al. 2018; Kehm et al. 2018). The main improvements were seen in C10, C20, and C40, the standard deviations of which are improved up to 30 %. Also, observations of GENESIS with VLBI would strengthen the integration of the Earth geometry, rotation and gravitational field. The Stokes coefficients are common parameters to all techniques such as a subgroup of the EOP, namely the terrestrial pole coordinates and its first derivatives (see Table 1).