The thought experiment of digging a straight hole through the Earth is a classic way to explore the planet’s vast geography and the extreme conditions of its interior. This journey, which ends at the exact opposite location, is defined by the geographic term “antipode.” An antipode is the point on the globe diametrically opposed to a specific location, connected by a line passing directly through the planet’s center. Understanding where you would exit requires a simple set of geographical calculations, while the possibility of the journey depends on confronting the geological realities of Earth’s layered structure and the laws of physics.
Calculating Your Antipodal Point
Determining your antipodal point is a straightforward exercise in coordinate inversion. This calculation involves taking your starting latitude and longitude and applying two simple rules. For the latitude, you simply flip the hemisphere: a starting point in the Northern Hemisphere will have an antipode in the Southern Hemisphere with the exact same degree measure.
The calculation for longitude requires subtracting your current longitude from 180 degrees, then switching the direction (East to West or vice-versa). For example, if you start at London, England (51.5 degrees North, 0 degrees West), your journey would end at 51.5 degrees South and 180 degrees East. This point places the exit in the South Pacific Ocean, east of New Zealand, near the Chatham Islands’ Waitangi settlement.
This geographical reality highlights a common misconception, as most people assume they would emerge on a landmass like China. Due to the uneven distribution of continents, the vast majority of land-based starting points have an antipode located in an ocean. The antipode of Los Angeles, for instance, is found deep within the Indian Ocean. Only a few large land areas are antipodal to one another, such as parts of East Asia (China and Mongolia) and certain regions of South America (Argentina and Chile).
The Geological Barriers to Digging Through
The greatest obstacle to this subterranean journey is the Earth’s physical structure, which is divided into four distinct layers: the crust, the mantle, the outer core, and the inner core. The thin crust, where the journey begins, is only about 5 to 70 kilometers thick, but beyond it, conditions quickly become extreme. Temperatures increase rapidly, reaching approximately 1,000° Celsius at the base of the crust.
Descending further, the mantle extends for nearly 2,900 kilometers and accounts for over 80% of the planet’s volume. While often described as molten, the mantle is actually solid silicate rock that flows like extremely viscous tar over geological time scales. At the boundary with the core, the temperature rises to about 4,000° Celsius, and the pressure is nearly 1.4 million times that of the surface.
The core is composed primarily of iron and nickel. The outer core is liquid, with temperatures between 4,000 and 5,000° Celsius, and its swirling convection currents create the Earth’s magnetic field. The inner core, though hotter (estimated 5,000° Celsius), is compressed into a solid sphere by immense pressure. No known material could withstand the combination of these extreme temperatures and the crushing lithostatic pressure required to maintain a tunnel through the Earth’s interior.
The Physics of a Hypothetical Tunnel Journey
Assuming a hypothetical, frictionless, vacuum-sealed tunnel already exists, the journey would be governed entirely by the planet’s gravitational field. A traveler dropped into the tunnel would begin with the acceleration of surface gravity (approximately 1G). As the traveler descends, the mass of the Earth pulling them would lessen, causing the force of gravity to decrease.
The traveler would reach maximum speed at the very center of the Earth, where the gravitational force from all directions perfectly cancels out, resulting in momentary weightlessness. After passing the center, the gravity field would begin to pull in the opposite direction, acting as a natural brake. This gravitational mechanics causes the entire trip to be a free-fall oscillation, much like a pendulum swing.
This theoretical journey is estimated to take a remarkably short time. Calculations based on a uniform-density Earth model suggest a travel time of about 42 minutes and 12 seconds. Using a more accurate model that accounts for the Earth’s varying density, the trip would take slightly less time, clocking in at approximately 38 minutes and 11 seconds. The traveler would need to grab the edge of the tunnel upon arrival at the antipode, or they would immediately fall back toward the center to repeat the oscillation.