Space Definition and 187 Discussions

Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a conceptual framework.
Debates concerning the nature, essence and the mode of existence of space date back to antiquity; namely, to treatises like the Timaeus of Plato, or Socrates in his reflections on what the Greeks called khôra (i.e. "space"), or in the Physics of Aristotle (Book IV, Delta) in the definition of topos (i.e. place), or in the later "geometrical conception of place" as "space qua extension" in the Discourse on Place (Qawl fi al-Makan) of the 11th-century Arab polymath Alhazen. Many of these classical philosophical questions were discussed in the Renaissance and then reformulated in the 17th century, particularly during the early development of classical mechanics. In Isaac Newton's view, space was absolute—in the sense that it existed permanently and independently of whether there was any matter in the space. Other natural philosophers, notably Gottfried Leibniz, thought instead that space was in fact a collection of relations between objects, given by their distance and direction from one another. In the 18th century, the philosopher and theologian George Berkeley attempted to refute the "visibility of spatial depth" in his Essay Towards a New Theory of Vision. Later, the metaphysician Immanuel Kant said that the concepts of space and time are not empirical ones derived from experiences of the outside world—they are elements of an already given systematic framework that humans possess and use to structure all experiences. Kant referred to the experience of "space" in his Critique of Pure Reason as being a subjective "pure a priori form of intuition".
In the 19th and 20th centuries mathematicians began to examine geometries that are non-Euclidean, in which space is conceived as curved, rather than flat. According to Albert Einstein's theory of general relativity, space around gravitational fields deviates from Euclidean space. Experimental tests of general relativity have confirmed that non-Euclidean geometries provide a better model for the shape of space.

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  1. mpross

    B Dark Energy, Dark Matter and the Speed of Light

    Quote from NASA: My understanding of dark energy is based on NASA's report:; were NASA state as follows: "It turns out that roughly 68% of the universe is dark energy. Dark matter makes up about 27%. The rest - everything on...
  2. M

    Power tower in space

    Hello, I'm wondering about the practicality and feasibility of building large power tower structures in space. I could imagine something like follows: Take a long structural beam which is positioned in alignment to the sun rays. At the end closest to the sun a receiver is placed. Consisting...
  3. NODARman

    B Gravity to infinity?

    Hi, mathematically in the F = GMm/r^2 equation r can be very close to infinity (or the size of the universe), but gravitational force always will be some number. But how is that in the real world? Let's say we have a perfectly empty universe but only with two sun-like stars. If they are away...
  4. J

    I Heating gasses in space -- How could we make a greenhouse in space?

    I was thinking the other day about green houses and how they would act in space or on another planet without an atmosphere. I know that green houses work on Earth by stopping convection but could they theoretically trap heat in a non atmospheric environment? I am imagining a material that allows...
  5. Spockishere

    I What frequencies can be captured by all of our instruments?

    And if there are an infinite amount of frequencies, doesn't that mean that an extraterrestrial civilization could be reaching out without us being able to receive their signals. And even if we did receive their signals, how would we understand their form of communication? What if they...
  6. Spockishere

    B How long would a 7ly trip feel like to you if you travel at 50000km/s

    let's say i would like to drop by one of my pals on a certain planet, 7ly away. I got to 42 years but it doesn't really sound correct.
  7. S

    I Are there types of spacetime where no symmetries are valid?

    We derive the most basic laws of physics from several fundamental symmetries (those from Noether's theorems, gauge symmetries, Lorentz symmetry...). But are there any types of spacetime where no symmetries, no matter how fundamental, would be valid? Any special metric, geometry or shape?
  8. Isopod

    B Could anything heat back up the core of Mars?

    My understanding of why Mars lost its atmosphere was because it cooled down too much internally and that when this happened, the planet lost its magnetic field that helped protect it from solar winds (which then ended up stripping away the planets atmosphere). Is there anything that people could...
  9. dirb

    Finding the angle and velocity at which a space station reaches the moon of the planet

    A station is orbiting a planet at a distance R1, a moon is orbiting the planet at distance R2 with the period T. The planet itself has a radius rp and a mass mp. We know that when an object adds its velocity at a point in the orbit, the height of the opposite orbit will increase. Determine the...
  10. N

    Circular motion -- Position of the Sun seen from an airplane crossing the Equator

    We know that ##v = \omega r## where ##r = R_{\text{E}} + h##. To compensate for the motion, the plane must fly along the equator at the same speed as the Earth but in the opposite direction, i.e. from east to west, so $$\vec{v} = -\vec{ v}_{\text{E}}$$ $$v_{\text{E}} = \omega_{\text{E}}...
  11. J

    The Genesis Project plans to use robots to seed the galaxy with life. Will this be possible in the future?
  12. W

    B According to current physics, is vacuum still something or nothing?

    Before that, Lawrence Kraus stated "Empty space is a boiling, bubbling brew of virtual particles that pop in and out of existence in a time scale so short that you can't even measure them" . After reading especially this statement...
  13. O

    B Untraditional Space Travel

    If an infinite amount of energy were available to create the lift mechanism for a space launch. What would be required to fire a 200lb object into low Earth orbit(160km) after speeding it up in a way similar to how the large hadron collider speeds up a particle. Assuming the launch vehicle...
  14. Viii

    Interplanetary cruise problem

    Summary:: You have a spacecraft the size of a cube (2x2x2 m^3, m=3000 kg. It has 24 thrusters (2N each) and one main engine. For preparing your spacecraft for maneuvers, you want to rotate by 180 degrees. For the rotation, you'll use n=4 attitude thrusters per burn. What am I doing wrong...
  15. D

    Work, Power, Energy, Efficiency

    The answer in the textbook says 0J but I am not sure what the concept behind it is. Does it have something to do with gravity?
  16. AlfSalte

    B What happens to time as space is expanding?

    I have one question I hope someone here can answer for me. Relativity theory tells us that space and time are sort of the same thing, as a spacetime. So when space is expanding, what happens to time? I find it hard to believe that time is somehow unaffected by the expansion of space, so while...
  17. Tone L

    Satellite failure

    I was thinking this past morning of the challenger explosion due to the stiff and cold failed O-rings in the fuel segments. I was trying to think of satellite failures, I couldn't find too much... Do you all know of satellite (components, instruments, etc) failures that occurred while in...
  18. K

    Ideas for novel I'm writing! I would love some insight on a concept!

    Summary:: Ideas for a novel I want to begin writing. Brainstorming ideas and need help with a certain concept. Any help is appreciated! Hello to you all, this is my first post, and I Google searched this astrophysics forum because I thought it might be a good place to begin asking for advice...
  19. S

    Converting State Vectors to Keplerian Orbital Elements for Binary Objects

    Homework Statement:: I'm working on a personal project to convert objects from a simulation using state vectors for position and velocity to Keplerian orbital elements (semimajor axis, eccentricity, argument of periapsis, etc.). However, the equations I am using do not calculate the...
  20. R

    B Torricelli Vacuum Experiment

    If Evangelista Torricelli truly created a vacuum, then there would be nothing in it, yet you can see through it which means light is obviously still in there (and who knows what else), right? If there was truly nothing in it, and glass is a highly viscous fluid, and fluids conform to fill empty...
  21. B

    I Distortion of Space Time

    Presume we look at a two-dimensional view of space time, with no local masses, and we draw a grid of equidistance spaced lines. The intent is to look at space but not time. As we begin, we look in all directions and the grid lines are evenly spaced. Begin adding mass to the center of the grid...
  22. Athenian

    [SR] - Test Particle inside the Sun's Gravitational Field - Part 4

    So, here's an attempted solution: With ##r_{min}##, $$r_{min} = \frac{1}{B + \frac{\beta}{\alpha^2}}$$ With ##r_{max}##, I get: $$r_{max} = \frac{1}{B - \frac{\beta}{\alpha^2}}$$ or $$r_{max} = \frac{1}{\frac{\beta}{\alpha^2}}$$ Other than this, I and the team have absolutely no idea on how...
  23. Athenian

    [SR] - Test Particle inside the Sun's Gravitational Field - Part 3

    Below, I have already solved - I assume - correctly for question 1. Question 2, I am nearing to what I believe is the solution. Question 3, I simply have no idea where I should begin considering that it is interconnected with question 2. With that said, below is the lengthy and somewhat tedious...
  24. Athenian

    [SR] - Test Particle inside the Sun's Gravitational Field - Part 2

    To begin with, I posted this thread ahead of time simply because I thought it may provide me some insight on how to solve for another problem that I have previously posted here:
  25. Athenian

    [Special Relativity] Test Particle Inside the Sun's Gravitational Field

    Below is an attempted solution based off of another user's work on StackExchange: Source: [] To begin with, I will be using the following equation mentioned in...
  26. K

    A Solar Rayleigh scattering power per molecule and photoionization rates for CO2, H2O

    I'm pondering the behavior and persistence of rocket exhaust plume molecules far above the atmosphere. For example, the plume from an apogee circularization thrust from GTO (Geosynchronous Transfer Orbit) to GEO (Geosynchronous orbit). CO₂ and H₂O are among the molecular species emitted by a...
  27. Quantum Alchemy

    B A Question about space and the multiverse

    My question is about space and the multiverse. I was reading work by Max Tegmark and he sees the multiverse as Level 1-4. A Level 1 multiverse seems like it's self evident and I was wondering about the evidence against it. It's simple: Space expands faster than we can observe it so we exist in...
  28. S

    A Is there any theory that can be modeled in any type of space?

    Is there any theory in physics that can be modeled in any type of space (Hilbert space, Euclidean, Non-Euclidean...etc)? And if yes, could that theory also contain/be compatible with all types of (physical) symmetries?
  29. J

    B How physics equations transform under inverse of parameters

    It is obvious that there is a one-to-one relationship between real numbers (defined to include infinity) and their multiplicative inverses (assuming we map the inverse of zero to infinity and vice versa). Thus, one should be able to replace the distance between two points in space with it's...
  30. G

    Understanding forced motion in space

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  31. Ryu

    Theoretical Higher spatial dimensions question

    So I had a topic which I would like to fact check from an informed scientific source. Basically there is an argument about whether or not an object that naturally exists in a fourth dimensional space, would by default have more than countably infinite times the energy of a 3 dimensional Object...
  32. H

    A peculiar world

    Hello everyone! I am an undergraduate getting three bachelors in Anthropology/Ecology/Neurosciences (just to show off of course), but sadly no true physics (I don't show off that much, I'm still humble). I am working on a personal project, a tabletop role playing game, where my main struggle is...
  33. JD_PM

    Physics Essential skills for applying for Space Agency jobs as a physicist

    Hi Physics Forums community. Let me briefly explain my current state of affairs. Next season, if every goes as planned, I will begin my Master's in Physics. I have, what I call, a positive problem; I like lots of branches of Physics (I study Physics because of pure passion and not because I...
  34. Antony Death

    B Is the current definition of gravity accurate?

    The current definition of Gravity is: The force of attraction between bodies as a result of their mass. Gravity affects both the space and time of the area surrounding a mass, diminishing with distance, so is the current accepted definition truly accurate? Do I have the correct definition and if...
  35. A

    Flight Path Angle and Velocity During Atmospheric Re-entry

    A space vehicle enters the sensible atmosphere of the Earth (300,000 ft) with a velocity of 25,000 ft/sec at a flight-path angle of -60 degrees. What is its velocity and flight-path angle at an altitude of 100 nautical miles during descent? (Assuming no drag or perturbations, two body orbital...
  36. Mr C Odd

    Time dilation in a magnetic field

    Hi all. I was wondering if time is dilated whilst traveling in a stable magnetic field that is generated by the object travelling, and if so, does this vary if you reduce or intensify the magnetic field? Also, what happens if the object is generating two opposing magnetic fields, would...
  37. H

    B Feasibility of a L1 Gravity Swing Cold Launch?

    At an L1 LaGrangian point between two bodies, one could - materials science notwithstanding - pit two of Newton's Laws (LM3,UG) against each other to provide thruster-free stationkeeping. Would it be feasible to use that to launch free from the system ? either spit out like a watermelon seed...
  38. V

    B Is space is continuous or discrete?

    I was watching a video where well known physicist Lisa Randall said that we still don't know whether space is continuous or discrete. My question is, how do we find whether space is continuous or discrete?? What type of experiments are possible? Is it being done now?? I am thinking this may be...
  39. M

    What would happen to a blob of mercury in space?

    How long would it take for a blob of mercury (the size of a marble or so) to freeze in space? I'd emagine it would have to boil in some way first, and that would send pieces of it flying around, but the surface tension of mercury is much greater than that of water, or urine (as we'd seen...
  40. S

    How do we know that light that comes from the stars is in past?

    So for some reason, from time to time, i always come back to this question and i can't remember that part of the physics while i was studying and most of the explanation are pretty generic. Basically how do we know that light actually travels and not just oscillate and transfer energy when...
  41. T

    I How can I go about making a "Space Proof" coating?

    So I am planning on launching a Satellite to promote the Dogecoin cryptocurrency. One of the main points is printing/painting (Or whatever) the logo on the side of a metal panel. How can I make it so it doesn't melt off or turn white from radiation so quickly?
  42. N

    If you threw a warm water balloon into space, would it boil?

    And by how much would the balloon expand, if at all?
  43. R

    I Question about time and space

    if the Earth were set between 2 Sun (our sun) in the distance which the time passes the exact same as it is right now, does the distance between us and each sun would be the same as it is right now?
  44. pairofstrings

    I Mathematical Structure and Mathematical Space Hierarchies

    Hi. I am trying to understand the images that I have posted below. Each layer of Mathematical Structure Hierarchy in the image in this post and Mathematical Space Hierarchy in the image in this post are: statements. 1. What do these statements of each layer of these hierarchies in the...
  45. R

    Materials for space applications?

    So I'm working on this project for a inflatable solar sail (so a spherical solar sail) and we are really only verifying the deployment of the sail in space (from a cubesat)...We are doing a mock PDR and I need to find info on the sail we'll be using. My job is to find an "off the shelf"...
  46. Kenneth Boon Faker

    B What does the 'space' inside an atom consist of?

    Atoms make up all the material stuff around us, but most of an atom is empty space. The nucleus at the centre of an atom (99.95 percent of its mass) is orbited by tiny electrons (only 0.05 percent or less of the overall atomic mass). And as you've probably heard, an analogy is to think of the...
  47. Craftek_Ana

    B Traveling to Mars and time dilation

    If/when we go to Mars how will we deal with time dilation due to the gravitational differences between the two planets?
  48. mjda

    Resolving bodies at large distances

    Homework Statement If a 6.5m diameter telescope operates at wavelengths between 600nm to 2800nm, and for stellar densities similar to the Solar neighbourhood, what is the range of distances this telescope can resolve individual stars? Homework Equations The Attempt at a Solution My attempts...
  49. R

    I Why does bent space set objects in motion?

    Two stationary masses will attract each other. That is, they start moving towards each other. For example, a stationary apple will fall to earth. I can see bent space affecting the trajectory of a moving object. ...but how does bent space explain that stationary objects start moving?
  50. David Dodson

    I Does space have its own density?

    Does space have its own density? i.e. a mass density distinct from the mass density of 'particles' in it? or may it have a uniform density of some kind of vast particle(s)? If so, would the effect on observable masses largely cancel out? One answer from...