Tekanan Negatif dalam Energi Gelap

Negative Pressure

Independently from its actual nature, dark energy would need to have a strong negative pressure in order to explain the observed acceleration in the expansion rate of the universe.

According to General Relativity, the pressure within a substance contributes to its gravitational attraction for other things just as its mass density does. This happens because the physical quantity that causes matter to generate gravitational effects is the Stress-energy tensor, which contains both the energy (or matter) density of a substance and its pressure and viscosity.

In the Friedmann-Lemaître-Robertson-Walker metric, it can be shown that a strong constant negative pressure in all the universe causes an acceleration in universe expansion if the universe is already expanding, or a deceleration in universe contraction if the universe is already contracting. More exactly, the second derivative of the universe scale factor, , is positive if the equation of state of the universe is such that w < − 1 / 3.

This accelerating expansion effect is sometimes labeled "gravitational repulsion", which is a colorful but possibly confusing expression. In fact a negative pressure does not influence the gravitational interaction between masses - which remains attractive - but rather alters the overall evolution of the universe at the cosmological scale, typically resulting in the accelerating expansion of the universe despite the attraction among the masses present in the universe.

Kunjungi Juga:

Central Research for Dark Energy & Dark Matter 

Wikipedia

Mengenal Sistem Transportasi Antariksa

"A man may die, nations may rise and fall, but an idea lives on." 

~John F. Kennedy~ 

Perkembangan Teknologi Antariksa di Indonesia, Indonesia belum pernah terlibat secara langsung dalam eksplorasi ruang angkasa, tetapi Indonesia sebenarnya termasuk negara yang cukup disegani karena pengalamannya dalam mengeksploitasi teknologi keantariksaan.

Saat penggunaan satelit bagi sebagian besar negara masih sangat jarang, Indonesia telah meluncurkan satelitnya yang pertama, Palapa A1 pada 9 Juli 1976. Ini mencatatkan Indonesia sebagai negara ketiga di dunia setelah AS dan Canada yang menggunakan satelit komunikasi domestiknya sendiri.

Indonesia juga sudah memanfaatkan jasanya untuk meluncurkan satelit Palapa generasi kedua, Palapa B1, pada 19 Juni 1983.

• SPACE SHUTTLE PROGRAM

• SPACE SHUTTLE REQUIREMENTS

• LAUNCH SITES

• BACKGROUND AND STATUS

• MISSION PROFILE

• ABORTS

• RETURN TO LAUNCH SITE OVERVIEW

• TRANSATLANTIC LANDING ABORT OVERVIEW

• ABORT TO ORBIT OVERVIEW

• ABORT ONCE AROUND OVERVIEW

• CONTINGENCY ABORT OVERVIEW

• ORBITER GROUND TURNAROUND

ORBITER MANUFACTURING AND ASSEMBLY

OPERATIONAL IMPROVEMENTS AND MODIFICATIONS

• ORBITER

• ORBITAL MANEUVERING SYSTEM/REACTION CONTROL

• SYSTEM AC-MOTOR-OPERATED VALVES

• PRIMARY RCS MODS

• FUEL CELL MODS

• AUXILIARY POWER UNIT MODS

• MAIN LANDING GEAR

• NOSE WHEEL STEERING MODS

• THERMAL PROTECTION SYSTEM MODS

• WING MODIFICATION

• MIDFUSELAGE MODIFICATIONS

• GENERAL-PURPOSE COMPUTERS

• INERTIAL MEASUREMENT UNIT MODS

• CREW ESCAPE SYSTEM

• EMERGENCY EGRESS SLIDE

• 17-INCH ORBITER/EXTERNAL TANK DISCONNECTS

• SPACE SHUTTLE MAIN ENGINE MARGIN IMPROVEMENT PROGRAM

• SSME FLIGHT PROGRAM

• SOLID ROCKET MOTOR REDESIGN

• ORIGINAL VERSUS REDESIGNED SRM FIELD JOINT

• ORIGINAL VERSUS REDESIGNED SRM CASE-TO-NOZZEL JOINT

• NOZZLE

• FACTORY JOINT

• PROPELLANT

• IGNITION SYSTEM

• GROUND SUPPORT EQUIPMENT

• DESIGN ANALYSIS SUMMARY

• VERIFICATION/CERTIFICATION TEST

• NON-DESTRUCTIVE EVALUATION

• CONTINGENCY PLANNING

• INDEPENDENT OVERSIGHT

Indonesia sebenarnya memiliki potensi yang jarang dimiliki negara lain untuk mengembangkan teknologi antariksanya sendiri. Potensi itu berupa garis katulistiwa yang membentang di atasnya. Sekitar 13% dari garis katulistiwa berada di atas wilayah Indonesia. Dengan demikian, Indonesia tercatat sebagai negara pemilik garis katulistiwa yang terpanjang di dunia.

Hal ini menjadikan wilayah Indonesia sebagai tempat yang sangat ideal untuk menjadi lokasi peluncuran roket pengangkut satelit. Peluncuran roket dari dekat garis katulistiwa akan lebih menghemat bahan bakar roket, dan karenanya lebih murah dari segi biaya.

To Be Continued

Sumber:

NASA
LAPAN
Wikipedia


 

Yuk Kita Mengenal Energi Gelap

Nature of dark energy

The exact nature of this dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense—roughly 10⁻²⁹ grams per cubic centimeter—it is hard to imagine experiments to detect it in the laboratory. 

Dark energy can only have such a profound impact on the universe, making up 74% of all energy, because it uniformly fills otherwise empty space. The two leading models are quintessence and the cosmological constant. Both models include the common characteristic that dark energy must have negative pressure.

Kunjungi Juga:

Central Research for Dark Energy & Dark Matter

Wikipedia